United States Patent Application |
20150142082
|
Kind Code
|
A1
|
Simon; Bruce J.
; et al.
|
May 21, 2015
|
SYSTEMS AND METHODS OF BIOFEEDBACK USING NERVE STIMULATION
Abstract
Devices, systems and methods are disclosed that are used to treat a
medical condition, by electrical stimulation of a nerve or nerve
ganglion, used in conjunction with biofeedback. The system comprises a
stimulator that applies electrical impulses sufficient to modulate a
nerve at a target site within the patient. A sensor measures a
physiological output from the patient, such as heart rate variability,
and a property of the stimulation signal is varied based on the
physiological output.
Inventors: |
Simon; Bruce J.; (Mountain Lakes, NJ)
; Errico; Joseph P.; (Warren, NJ)
|
Applicant: | Name | City | State | Country | Type | ElectroCore, LLC | Basking Ridge | NJ | US
| | |
Assignee: |
ElectroCore, LLC
Basking Ridge
NJ
|
Family ID:
|
53174055
|
Appl. No.:
|
14/080885
|
Filed:
|
November 15, 2013 |
Current U.S. Class: |
607/61 ; 607/62 |
Current CPC Class: |
A61N 1/36053 20130101; A61N 1/36132 20130101; A61N 1/36139 20130101 |
Class at Publication: |
607/61 ; 607/62 |
International Class: |
A61N 1/36 20060101 A61N001/36 |
Claims
1. A system for treating a medical condition of a patient, comprising: a
physiological sensor that produces a physical output that is a
measurement of a property of a physiological parameter of the patient; a
stimulator comprising one or more electrodes; and a signal generator
configured to generate one or more electrical impulses and transmit the
one or more electrical impulses through the one or more electrodes to a
nerve at a target region within the patient, wherein the one or more
electrical impulses vary in response to the physical output from the
physiological sensor.
2. The system of claim 1, wherein the stimulator is configured for
implantation in the patient at the target site.
3. The system of claim 2, wherein the signal generator is configured for
implantation in the patient at the target site.
4. The system of claim 3, further comprising a power source configured to
transmit electrical energy through an outer skin surface of the patient
to the stimulator to power the signal generator.
5. The system of claim 1, wherein the stimulator comprises a housing
having an electrically permeable contact surface for contacting an outer
skin surface of the patient and an energy source within the housing
configured to generate the one or more electrical impulses, and wherein
the one or more electrical impulses is of a sufficient energy level to be
transmitted through the outer skin surface of the patient to the nerve at
the target region within the patient.
6. The system of claim 1, further comprising a device configured to
permit stimulation of an exteroceptive sense of the patient with a
biofeedback signal that varies in response to the physical output from
the physiological sensor, wherein the nerve and/or a mental reaction of
the patient to the biofeedback signal can control the property of the
physiological parameter, thereby controlling the output from the sensor,
such that the medical condition of the patient is treated.
7. The system of claim 1, wherein the physiological sensor is configured
to measure the patient's heart rate variability, electromyogram,
electroencephalogram, galvanic skin response, temperature, or blood flow.
8. The system of claim 7, wherein the stimulator is configured to vary a
property of the one or more electrical impulses based on the physical
output from the physiological sensor.
9. The system of claim 8, wherein the property is one of a frequency,
amplitude, and duty cycle.
10. The system of claim 1, wherein the stimulator is configured to allow
the patient to modulate an amplitude of the one or more electrical
impulses by consciously modulating output from the physiological sensor,
through the mental reaction of the patient to the biofeedback signal.
11. The system of claim 5, wherein the energy source comprises a signal
generator and one or more electrodes coupled to the signal generator
within the housing.
12. The system of claim 11, further comprising a conducting medium within
the housing between the one or more electrodes and the electrically
permeable contact surface.
13. The system of claim 1, wherein the one or more electrical impulses is
configured to modulate a nerve fiber at the target region and is also
configured to electrically stimulate a tactile exteroceptive sense.
14. The system of claim 1, wherein the one or more electrical impulses is
configured to modulate a nerve fiber at the target region, and wherein
the one or more electrical impulses is configured to not substantially
modulate a nerve or muscle between an outer skin surface and the target
region if the exteroceptive sense is not tactile.
15. The system of claim 1, wherein the one or more electrical impulses is
sufficient to stimulate a vagus nerve of the patient.
16. The system of claim 15, wherein the one or more electrical impulses
is configured to produce an interoceptive sensation in the patient,
wherein a mental reaction of the patient to the interoceptive sensation
can control the property of the physiological entity.
17. A method for treating a medical condition of a patient, comprising:
sensing a physiological parameter of a patient; producing a physical
output that is a measurement of the physiological parameter; generating
one or more electrical impulses directed at a nerve within the patient
sufficient to modulate the nerve; and varying a property of the one or
more electrical impulses based on the physical output.
18. The method of claim 17, wherein the generating is carried out by
implanting a stimulator at a target site within the patient.
19. The method of claim 18, further comprising transmitting electrical
energy from a power source external to the patient to the stimulator.
20. The method of claim 17, wherein the nerve is at the target site, and
wherein the generating is carried out by transmitting the electrical
impulse through an outer skin surface of the patient to the nerve at the
target site.
21. The method of claim 17, further comprising stimulating an
exteroceptive sense of the patient with a biofeedback signal that varies
in response to the physical output to allow the patient to control output
from the sensor.
22. The method of claim 17, wherein the sensing comprises measuring the
patient's heart rate variability, electromyogram, electroencephalogram,
galvanic skin response, temperature, or blood flow.
23. The method of claim 17, wherein the property is one of a frequency,
amplitude, and duty cycle.
24. The method of claim 21, further comprising allowing the patient to
modulate an amplitude of the one or more electrical impulses by
consciously modulating output from the sensor, through the mental
reaction of the patient to the biofeedback signal.
25. The method of claim 17, wherein the one or more electrical impulses
is configured to modulate a nerve fiber at a target region and is also
configured to electrically stimulate a tactile exteroceptive sense.
26. The method of claim 17, wherein the one or more electrical impulses
is sufficient to stimulate a vagus nerve of the patient.
Description
FIELD
[0001] The field of the present invention relates to the delivery of
energy impulses (and/or energy fields) to bodily tissues for therapeutic
purposes. The invention relates more specifically to the use of
biofeedback with noninvasive nerve stimulation.
BACKGROUND OF THE INVENTION
[0002] As background to the objectives of the present invention and their
relation to biofeedback methods that are currently practiced, the
following paragraphs describe the rationale for biofeedback methods and
their current limitations. At least some of the objectives of the
invention are met by adapting vagus nerve stimulation (VNS) devices and
methods for use with biofeedback. Therefore, current uses of VNS devices
are also summarized below as background information.
[0003] The human nervous system consists of the central nervous system
(brain and spinal cord) and the peripheral nervous system, the latter
containing nerves connecting the central nervous system to the rest of
the body. The peripheral nervous system in turn consists of the somatic
nervous system and the autonomic nervous system (ANS), with the ANS also
being connected to the semi-autonomous nervous system of the gut (the
enteric nervous system).
[0004] The somatic nervous system is associated with the voluntary control
of body movements via skeletal muscles. The ANS controls visceral
functions and operates largely below the level of consciousness. Thus,
the autonomic nervous system can control physiological process without
conscious effort, such as the beating of the heart, digestion,
respiration, salivation, perspiration, pupil dilation, and micturition.
Basic aspects of ANS control are exercised locally within an end organ.
However, global and integrative control is also exercised via specialized
components of the brainstem and other regions of the central nervous
system that receive both visceral and somatic sensory afferent
information from nerves ending in the organs of the body, process that
information, and then send control signals back to the visceral organs
and skeletal muscle via efferent nerves and via blood-borne hormones. The
central autonomic network includes the insula and medial prefrontal
cortex, the central nucleus of the amygdala, the preoptic region, the
hypothalamus, the midbrain periaqueductal grey matter, the pontine
parabrachial region, the nucleus of the solitary tract, and the
intermediate reticular zone of the medulla [SAPER C B. The central
autonomic nervous system: conscious visceral perception and autonomic
pattern generation. Annu Rev Neurosci 25(2002):433-469; John C.
LONGHURST. Regulation of autonomic function by visceral and somatic
afferents. Chapter 9, pp 161-179. In: Ida J Llewellyn-Smith and Anthony J
M Verbone (eds). Central Regulation of Autonomic Functions, 2nd Ed. New
York: Oxford University Press, 2011; SAPER CB. The central autonomic
system. Chapter 24, pp. 761-796. In: The Rat Nervous System, 3rd Edn., G
Paxinos (Ed.), Amsterdam, Boston: Elsevier, Academic Press. 2004].
[0005] It has been known for many years that some individuals have unusual
voluntary control over visceral functions, serving as apparent exceptions
to the general rule that control of visceral organs is autonomous and
non-voluntary. For example, some individuals are able to voluntarily
increase their heart rate at will [H F WEST and W E Savage. Voluntary
acceleration of the heart beat. Archives of Internal Medicine
22(1918):290-295; John T. KING, Jr. An instance of voluntary acceleration
of the pulse. Bull. Johns Hopkins Hosp. 31(1920): 303-305; H FEIL, HD
Green, D Eiber. Voluntary acceleration of heart in a subject showing the
Wolff-Parkinson-White syndrome: clinical, physiologic, and pharmacologic
studies. Am Heart J. 34(3, 1947):334-348]. If voluntary visceral control
could be imparted or taught to members of the population at large, this
would potentially constitute a major medical advance, considering that
dysautonomias and the many other diseases involving the ANS might be
treated without the risk of side effects that now accompany their
treatment using drugs. Furthermore, such voluntary autonomic regulation
would have the virtue that it could be applied episodically, only when it
is needed, for example, to calm a potentially racing heartbeat at the
onset of a panic attack.
[0006] It is conceivable that the rare individuals who can voluntarily
control autonomic functions such as heart rate, eye-pupil diameters,
piloerection ("goose bumps" or cutis anserina), etc., do so via direct
neural connections between the portions of the brain involved in volition
and the central autonomic nervous system that connects to efferent
visceral and motor nerves [LINDSLEY, D. B. and Sassaman, W. H. Autonomic
activity and brain potentials associated with `voluntary` control of the
pilomotors. Journal of Neurophysiology 1(1938):342-349]. However, it is
more plausible that the visceral control may be indirect, through
voluntary muscular control that also affects the viscera, or through
voluntary control over the circuits of the brain affecting emotions,
which in turn affect the autonomic state of the viscera during fear,
anger, pain, joy, etc., or by otherwise taking advantage of classically
acquired (Pavlovian) conditional reflexes [Joseph E. LEDOUX. Emotion
circuits of the brain. Annu Rev Neurosci 23(2000):155-184; KREIBIG S D.
Autonomic nervous system activity in emotion: a review. Biol Psychol 84
(3, 2010):394-421; CRITCHLEY H D. Neural mechanisms of autonomic,
affective, and cognitive integration. J Comp Neurol 493(1, 2005):154-166;
DWORKIN B R, Dworkin S. Learning of physiological responses: II.
Classical conditioning of the baroreflex. Behav Neurosci 109(6,
1995):1119-1136].
[0007] As an example of emotional indirect control over the autonomic
nervous system, patients paralyzed from the neck down suffer severe
hypotension when they are moved from a horizontal to an upright position.
Nevertheless, despite their muscular paralysis, some of them can learn to
increase their blood pressure when needed, as a countermeasure. When
asked how they do so, they report using emotional strategies, such as
getting angry about the unfairness their condition, or getting excited by
having sexual thoughts [Neal E. MILLER. Biomedical foundations for
biofeedback as a part of behavioral medicine. Chapter 2, pp. 5-15 In:
John V. BASMAJIAN (ed). Biofeedback--Principles and Practices for
Clinicians, 3rd Edn. Baltimore: Williams & Wilkins, 1989]. The voluntary
control of autonomic functions could even be doubly indirect if the
circuits of the brain affecting emotions cause involuntary muscular
contractions (analogous to facial grimacing) or widespread muscular
relaxation, which in turn affect the autonomic end organ.
[0008] In regards to potential voluntary muscular control that also
affects the viscera, it is understood that many physiological systems
have dual voluntary and involuntary components, the classic example of
which is blinking of the eye [S. R. COLEMAN and Sandra Webster. The
problem of volition and the conditioned reflex. Part II. Voluntary
responding subjects, 1951-1980. Behaviorism 16(1, 1988):17-49].Other
examples include respiration and micturition. For example, individuals
may voluntarily control their diaphragm to modulate the rate and depth of
respiration, which in turn affects the heart rate and blood pressure
through physiological processes such as respiratory sinus arrhythmia,
pulsus paradoxus, and the like. Another example is that some Yogi have
developed the ability to apply muscular tension to their abdomen and
thorax with closed glottis, retarding venous return to the heart, thereby
reflexively affecting the heart rate and blood pressure [M WENGER, B
Baghi, and B Anand. Experiments in India on "voluntary" control of the
heart and the pulse. Circulation 24(1961):1319-1325]. It is conceivable
that other individuals may be born with, or acquire, the unusual ability
to tense or relax specific skeletal muscles, e.g., around the vagus nerve
or baroreceptors in the neck, which in turn could cause reflex changes in
the heart rate and blood pressure. Such muscles need not be under
voluntary control in the normal course of neuromuscular development, but
might become so in a subset of the population at large [J. H. BAIR.
Development of voluntary control. Psychological Review 8(5,
1901):474-510]. A more generalized muscular tensioning might also
modulate the autonomic functioning of the viscera, e.g., analogous to
what happens during isometric exercise, and a general muscular relaxation
may secondarily modulate blood flow within the peripheral circulation by
changing the mechanical or chemical environment of the blood vessels
collectively, or by reducing the availability of adenosine for
sympathetic activation [COSTA F, Biaggioni I. Role of adenosine in the
sympathetic activation produced by isometric exercise in humans. J Clin
Invest.93(1994):1654-1660].
[0009] In the early 1960s, several publications suggested that most
individuals could learn to voluntarily control autonomic functions, such
as heart rate, vasoconstriction, salivation, intestinal contraction, and
galvanic skin response (GSR), but they did not address the issue of
direct versus indirect voluntary control [H. D. KIMMEL. Instrumental
conditioning of autonomically mediated behavior. Psychological Bulletin
67(1967):337-345; H. D. KIMMEL. Instrumental conditioning of
autonomically mediated responses in human beings. American Psychologist
29(5, 1974):325-335]. A landmark publication in 1969 by MILLER had a
profound influence on work concerning whether the viscera could be
controlled directly and voluntarily [Neal E MILLER. Learning of visceral
and glandular responses. Science 163(3866, 1969):434-445]. That
publication described the use of operant conditioning (also known as
instrumental conditioning or Skinnerian conditioning) to train animals to
control their heart rate and other visceral functions. Operant
conditioning is distinguished from classical conditioning (Pavlovian or
respondent conditioning) in that operant conditioning deals with the
modification of voluntary behavior, through the use of reinforcement and
punishment. Whereas Pavlovian responses are involuntarily reflexive and
involve stimulus events that precede the learned response, in contrast,
during operant conditioning, the reinforcement or punishment follows the
learned response that is performed voluntarily. In the experiments by
MILLER and colleagues, animals were temporarily paralyzed with curare and
were mechanically ventilated, in order to eliminate the possibility that
muscular contraction was responsible for the purported learned ability to
voluntarily change heart rate and other visceral physiological variables
that were investigated.
[0010] The results that were described by MILLER had broad implications
and spawned a great deal of related work by other investigators over the
following two decades, particularly work that is described below as the
use of biofeedback [Neal E. MILLER. Biofeedback and visceral learning.
Ann. Rev. Psychol. 29(1978):373-404]. However, his experimental results
were eventually determined to be irreproducible and were retracted, and
the conduct of the assistant who performed much of the actual laboratory
work became suspect before he committed suicide [Barry R. DWORKIN and
Neal E. Miller. Failure to replicate visceral learning in the acute
curarized rat preparation. Behavioral Neuroscience 100(3, 1986):299-314;
Marion NOTT. Are the claims true? The Evening Independent (St.
Petersburg, Fla.) Oct. 3, 1977, page 11]. Despite the still-frequent
citation of the work that MILLER has long since retracted, there is
currently no credible evidence that any mammal can directly and
voluntarily control visceral autonomic functions, such as heart rate. In
fact, it is thought that the direct, voluntary control of visceral
autonomic functions is not possible in principle, unless it were to be
accompanied by the adaptation of internal bodily sensors that operate
largely below the level of consciousness (interoceptors, see below)
[Barry R. DWORKIN. Learning and Physiological Regulation. Chicago:
University of Chicago Press, 1993, Chapter 8, pp. 162-185]. However, as
described above, voluntary control over the viscera might be exerted
indirectly via skeletal muscles or through voluntary modulation of an
individual's emotional state. With this in mind, one objective of the
present invention is to teach methods and devices that actually enable
most individuals to directly and voluntarily control visceral autonomic
functions, with or without simultaneous indirect voluntary control via
skeletal muscle or emotion.
[0011] One explanation for our inability to voluntarily control visceral
function is that the conscious mind cannot generally sense the state of
the viscera, so one would have little conscious basis for directing
voluntary visceral control, even if control over efferent nerves
modulating activity of the end organs could be voluntarily exercised. In
fact, the body contains many types of internal sensors (interoceptors)
that operate largely below the level of consciousness, including
baroreceptors and mechanoceptors, chemoreceptors, theromoreceptors, and
osmoreceptors. Sensors located in skeletal muscles, ligaments, and bursae
(proprioceptors) sense information related to muscle strain, location and
orientation. Sensors that respond to painful stimuli (nociceptors) may be
like other interoceptors, except that they generally have a small
diameter (A-delta and C fibers) and convey signals to the central nervous
system with a high frequency of discharge only after a threshold in the
stimulus has been exceeded. In contrast to other peripheral sensors,
nociceptors also do a poor job of discriminating the location of the
stimulus, and they convey their signals via a special anterolateral route
up the spinal cord to the thalamus. To the extent that one is conscious
of the state of the viscera, e.g., during painful internal stimuli
(stomach ache, angina pectoris, etc.), that awareness appears to result
from interoceptive representation that first reaches the thalamus and
eventually resides in the brain's right anterior insula, working in
conjunction with the adjoining frontal operculum and the anterior
cingulate cortex [Dieter VAITL. Interoception. Biological Psychology 42
(1996):1-27; CRITCHLEY H D, Wiens S, Rotshtein P, Ohman A, Dolan R J.
Neural systems supporting interoceptive awareness. Nat Neurosci 7(2,
2004):189-195; CRAIG, A. D. How do you feel? Introception: the sense of
the physiological condition of the body. Nat. Rev. Neurosci
3(2002):655-666; CRAIG AD. How do you feel--now? The anterior insula and
human awareness. Nat Rev Neurosci 10(1, 2009):59-70].
[0012] In order to make an individual artificially conscious of the
otherwise unperceived state of an internal organ, investigators may
electrically transduce a physiological signal, then use the magnitude of
that signal to generate a proportionate signal that may be sensed by one
of the individual's external senses. The generated signal is ordinarily
an audio or visual representation of the magnitude of the transduced
physiological signal. However, the generated signal may also be directed
to another exteroceptive sense, e.g., using electrical stimulation,
tactile stimulation with vibration or pressure, thermal stimulation, or
olfactory stimulation. The sensed and generated signals may even be
transmitted over a computer network [U.S. Pat. No. 7,150,715, entitled
Network enabled biofeedback administration, to COLLURA et al]. The
individual whose physiological signal is being transduced may then
voluntarily respond mentally to the magnitude of the generated signal. To
the extent that the individual learns to control his or her body in such
a way as to voluntarily modulate the value of the transduced
physiological signal, then the patient is said to have learned to perform
biofeedback.
[0013] According to rules of the U.S. Food and Drug Administration, "a
biofeedback device is an instrument that provides a visual or auditory
signal corresponding to the status of one or more of a patient's
physiological parameters (e.g., brain alpha wave activity, muscle
activity, skin temperature, etc.) so that the patient can control
voluntarily these physiological parameters . . . . " [21 CFR
882.5050--Biofeedback device]. The individual will not necessarily be
able to understand or explain how the voluntary control over the
physiological signal has been achieved. Such biofeedback may also be
considered to be a form of instrumental operant learning, in which the
reward to the individual is the satisfaction of being able to voluntarily
control the transduced physiological signal [Frank ANDRASIK and Amanda O.
Lords. Biofeedback. Chapter 7, pp. 189-214 In: Lynda W. Freeman, ed.
Mosby's Complementary & Alternative Medicine A Research-based Approach.
St. Louis, Mo.: Mosby Elsevier, 2009; John V. BASMAJIAN.
Biofeedback--Principles and Practices for Clinicians, 3rd Edn. Baltimore:
Williams & Wilkins, 1989 pp 1-396; Mark S. SCHWARTZ (ed). Biofeedback. A
Practitioner's Guide (2nd. Ed). New York: Guilford Press, 1995. pp
1-908].
[0014] Biofeedback methods and devices have been used in an attempt to
manage many medical conditions including: anxiety, attention deficit
hyperactivity disorder, chronic pain, constipation, epilepsy, headache,
hypertension, motion sickness, Raynaud's disease, temporomandibular
disorder, alcoholism/substance abuse, arthritis, diabetes mellitus, fecal
incontinence, insomnia, traumatic brain injury, vulvar vestibulitis,
asthma, autism, bell's palsy, cerebral palsy, chronic obstructive
pulmonary disease, coronary artery disease, cystic fibrosis, depressive
disorders, erectile dysfunction, fibromyalgia/chronic fatigue syndrome,
hand dystonia, multiple sclerosis, irritable bowel syndrome,
post-traumatic stress disorder, repetitive strain injury, respiratory
failure, stroke, tinnitus and urinary incontinence. However, in general,
biofeedback methods have only been clearly successful in connection with
conditions over which the individual has some voluntary muscular control.
The controlled muscles may be those associated with elimination disorders
(urinary incontinence, fecal incontinence, chronic constipation, levator
ani syndrome), temporomandibular joint syndrome, neuromuscular
rehabilitation after stroke and traumatic brain injury, and muscles of
the face, neck, and elsewhere that are overly-tensed during headaches and
other stress-related conditions [Anonymous. AETNA clinical policy
bulletin: Biofeedback. Policy No. 0132, last review Apr. 19, 2013. Aetna
Inc., 151 Farmington Avenue, Hartford, Conn. 06156; GLAZER H I, Laine C
D. Pelvic floor muscle biofeedback in the treatment of urinary
incontinence: a literature review. Appl Psychophysiol Biofeedback 31(3,
2006):187-201; CRIDER A, Glaros A G, Gevirtz R N. Efficacy of
biofeedback-based treatments for temporomandibular disorders. Appl
Psychophysiol Biofeedback 30(4, 2005):333-345; PALSSON O S, Heymen S,
Whitehead W E. Biofeedback treatment for functional anorectal disorders:
a comprehensive efficacy review. Appl Psychophysiol Biofeedback 29(3,
2004):153-174; William J. MULLALLY, Kathryn Hall M S, and Richard
Goldstein. Efficacy of Biofeedback in the Treatment of Migraine and
Tension Type Headaches. Pain Physician 12(2009):1005-1011; Yvonne
NESTORIUC, Alexandra Martin, Winfried Rief, Frank Andrasik. Biofeedback
Treatment for Headache Disorders: A Comprehensive Efficacy Review. Appl
Psychophysiol Biofeedback 33(2008):125-140; Carolyn YUCHA and Doil
Montgomery. Evidence-Based Practice in Biofeedback and Neurofeedback.
Wheat Ridge Colo.: The Association for Applied Psychophysiology and
Biofeedback, 2008. pp. 1-81; FRANK D L, Khorshid L, Kiffer J F, Moravec C
S, McKee M G. Biofeedback in medicine: who, when, why and how? Ment
Health Fam Med 7(2, 2010):85-91].
[0015] Biofeedback has been considerably less successful in managing
conditions involving autonomic or central nervous systems in which there
is little or no involvement of skeletal muscles. By way of example, it
has been shown that some individuals can learn to voluntarily change
their heart rate to some extent using biofeedback methods, but the
magnitude and reliability of that change are not sufficient to be useful
in the management of tachycardia, AV conduction problems, premature
ventricular contractions, and the like [Theodore WEISS. Biofeedback
training for cardiovascular dysfunctions. Med Clin North Am 61(4,
1977):913-928; Martin T. ORNE. The efficacy of biofeedback therapy. Ann
Rev Med 30(1979):489-503; Iris R. BELL and Gary E. Schwartz. Voluntary
control and reactivity of human heart rate. Psychophysiology 12(3, 1975):
339-348; ABUKONNA A, Yu X, Zhang C, Zhang J. Volitional control of the
heart rate. Int J Psychophysiol. Jun. 26 2013, pp. 1-6]. Furthermore,
many, if not most, individuals are unable to voluntarily change their
heart rate without deliberately taking advantage of respiratory sinus
arrhythmia or some similar reflex mechanism. Currently, the best use of
biofeedback for cardiac problems appears to be only in the promotion of
relaxation, by decreasing over-activation of the sympathetic branch of
the ANS, and up-regulating the contribution of the parasympathetic branch
of the ANS, to ultimately produce changes in the cellular and molecular
properties of the heart that enhance biological remodeling of cardiac
muscle and coronary blood vessels. However, the biofeedback effects are
apparently small, and the procedures may also make use of many simpler,
complementary or competing therapies, such as relaxation response therapy
[Linda KRANITZ and Paul Lehrer. Biofeedback applications in the treatment
of cardiovascular diseases. Cardiology in Review 12(2004): 177-181;
Christine S. MORAVEC. Biofeedback therapy in cardiovascular disease:
Rationale and research overview. Cleveland Clinic Journal of Medicine
75(Supp. 2, 2008):535-538; Christine S. MORAVEC and Michael G. McGee.
Biofeedback in the treatment of heart disease. Cleveland Clinic Journal
of Medicine 78(Supp. 1, 2011):520-523; Herbert BENSON, Jamie B. Kotch,
and Karen D. Crassweller. The relaxation response. A bridge between
psychiatry and medicine. Med Clin North Am 61(4, 1977):929-938].
[0016] Examples of other such conditions in which the use of biofeedback
has been of limited usefulness include: asthma, epilepsy, various mental
health conditions, and conditions affecting blood vessels (e.g.,
hypertension, Reynaud's phenomenon). For such conditions, the use of
biofeedback is currently often limited to individuals for whom
pharmacological therapy is contraindicated or in which there is no
preferred treatment [J GREENHALGH, R Dickson, and Y Dunbar. The effects
of biofeedback for the treatment of essential hypertension: a systematic
review. Health Technology Assessment 13:(46, 2009):1-104; NAKAO M, Yano
E, Nomura S, Kuboki T. Blood pressure-lowering effects of biofeedback
treatment in hypertension: a meta-analysis of randomized controlled
trials. Hypertens Res 26(1, 2003):37-46; ANONYMOUS. Comparison of
sustained-release nifedipine and temperature biofeedback for treatment of
primary Raynaud phenomenon. Results from a randomized clinical trial with
1-year follow-up. Arch Intern Med 160(8, 2000):1101-1108; Thomas RITZ,
Bernhard Dahme, and Walton T. Roth. Behavioral interventions in asthma.
Biofeedback techniques. Journal of Psychosomatic Research 56
(2004):711-720; Yoko NAGAI. Biofeedback and epilepsy. Curr Neurol
Neurosci Rep 11(2011):443-450; Kathi J. KEMPER. Biofeedback and mental
health. Alternative and Complementary Therapies 16 (4, 2010):208-212].
[0017] To the extent that currently-practiced biofeedback techniques are
helpful for some conditions that do not involve skeletal muscles, the
mechanism appears to be in helping the patient cope with the annoyance or
debilitation of a condition, rather than in actually addressing the
underlying pathophysiology of the condition. For example, there is no
evidence that biofeedback for tinnitus sufferers stops or prevents actual
ringing in the ears, but because distress from tinnitus is related to the
individual's perceived state of psychological stress, biofeedback that is
directed at reducing the stress may be helpful [ANONYMOUS. Evaluation and
Treatment of Tinnitus: A Comparative Effectiveness Review. Agency for
Healthcare Research and Quality 540 Gaither Road Rockville, Md. 20850,
Feb. 22, 2012, pp. 1-38; George HARALAMBOUS, Peter H. Wilson, Sarah
Platt-Hepworth, John P. Tonkin, V. Rae Hensley, David Kavanagh. EMG
biofeedback in the treatment of tinnitus: An experimental evaluation.
Behaviour Research and Therapy 25(1, 1987):49-55; Bernard LANDIS and
Erica Landis. Is biofeedback effective for chronic tinnitus? An intensive
study with seven subjects. American Journal of Otolaryngology 13(6,
1992): 349-356]
[0018] Apart from medical uses, biofeedback has also been used to teach
musicians and athletes relaxation and improved motor skills. Biofeedback
has also been used to improve the performance of workers in industrial
settings. Although the effectiveness of biofeedback is demonstrable when
the objective is to develop or reduce tension in specific skeletal
muscles, the efficacy of biofeedback that is used only for relaxation may
be no better than other common, inexpensive relaxation methods [Robert
CUTIETTA. Biofeedback training in music: from experimental to clinical
applications. Bulletin of the Council for Research in Music Education 87
(Spring, 1986):35-42; W. Alex EDMONDS and Gershon Tenenbaum, eds. Case
Studies in Applied Psychophysiology. Neurofeedback and Biofeedback
Treatments for Advances in Human Performance. Chichester, UK:
Wiley-Blackwell, 2012, pp. 1-292; A. P. SUTARTO, M. N. A. Wahab, N. M.
Zin. Heart Rate Variability (HRV) biofeedback: A new training approach
for operator's performance enhancement. Journal of Industrial Engineering
and Management 3(1, 2010):176-198].
[0019] VNS was developed initially for the treatment of partial onset
epilepsy and was subsequently developed for the treatment of depression
and other disorders. The left vagus nerve is ordinarily stimulated at a
location within the neck by first implanting an electrode about the vagus
nerve during open neck surgery and by then connecting the electrode to an
electrical stimulator circuit (a pulse generator). The pulse generator is
ordinarily implanted subcutaneously within a pocket that is created at
some distance from the electrode, which is usually in the left
infraclavicular region of the chest. A lead is then tunneled
subcutaneously to connect the electrode assembly and pulse generator. The
patient's stimulation protocol is then programmed using a device (a
programmer) that communicates with the pulse generator, with the
objective of selecting electrical stimulation parameters that best treat
the patient's condition (pulse frequency, stimulation amplitude, pulse
width, etc.) [U.S. Pat. No. 4,702,254 entitled Neurocybernetic
prosthesis, to ZABARA; U.S. Pat. No. 6,341,236 entitled Vagal nerve
stimulation techniques for treatment of epileptic seizures, to OSORIO et
al; U.S. Pat. No. 5,299,569 entitled Treatment of neuropsychiatric
disorders by nerve stimulation, to WERNICKE et al; G. C. ALBERT, C. M.
Cook, F. S. Prato, A. W. Thomas. Deep brain stimulation, vagal nerve
stimulation and transcranial stimulation: An overview of stimulation
parameters and neurotransmitter release. Neuroscience and Biobehavioral
Reviews 33 (2009):1042-1060; GROVES D A, Brown V J. Vagal nerve
stimulation: a review of its applications and potential mechanisms that
mediate its clinical effects. Neurosci Biobehav Rev 29(2005):493-500;
Reese TERRY, Jr. Vagus nerve stimulation: a proven therapy for treatment
of epilepsy strives to improve efficacy and expand applications. Conf
Proc IEEE Eng Med Biol Soc. 2009; 2009:4631-4634; Timothy B. MAPSTONE.
Vagus nerve stimulation: current concepts. Neurosurg Focus 25 (3,
2008):E9, pp. 1-4; ANDREWS, R. J. Neuromodulation. I. Techniques-deep
brain stimulation, vagus nerve stimulation, and transcranial magnetic
stimulation. Ann. N. Y. Acad. Sci. 993(2003):1-13; LABINER, D. M., Ahern,
G. L. Vagus nerve stimulation therapy in depression and epilepsy:
therapeutic parameter settings. Acta. Neurol. Scand. 115(2007):23-33;
AMAR, A. P., Levy, M. L., Liu, C. Y., Apuzzo, M. L. J. Vagus nerve
stimulation. Proceedings of the IEEE 096(7, 2008):1142-1151; BEEKWILDER J
P, Beems T. Overview of the clinical applications of vagus nerve
stimulation. J Clin Neurophysiol 27(2, 2010):130-138; CLANCY J A,
Deuchars S A, Deuchars J. The wonders of the Wanderer. Exp Physiol 98(1,
2013):38-45].
[0020] Unlike conventional vagus nerve stimulation, which involves the
surgical implantation of electrodes about the vagus nerve, the present
use of vagus nerve stimulation is non-invasive. Non-invasive procedures
are distinguished from invasive procedures (including minimally invasive
procedures) in that the invasive procedures insert a substance or device
into or through the skin (or other surface of the body, such as a wound
bed) or into an internal body cavity beyond a body orifice. For example,
transcutaneous electrical stimulation of a nerve is non-invasive because
it involves attaching electrodes to the skin, or otherwise stimulating at
or beyond the surface of the skin or using a form-fitting conductive
garment, without breaking the skin [Thierry KELLER and Andreas Kuhn.
Electrodes for transcutaneous (surface) electrical stimulation. Journal
of Automatic Control, University of Belgrade 18(2, 2008):35-45; Mark R.
PRAUSNITZ. The effects of electric current applied to skin: A review for
transdermal drug delivery. Advanced Drug Delivery Reviews 18 (1996)
395-425].
[0021] Another form of non-invasive electrical stimulation is magnetic
stimulation. It involves the induction, by a time-varying magnetic field,
of electrical fields and current within tissue, in accordance with
Faraday's law of induction. Magnetic stimulation is non-invasive because
the magnetic field is produced by passing a time-varying current through
a coil positioned outside the body. An electric field is induced at a
distance, causing electric current to flow within electrically conducting
bodily tissue. The electrical circuits for magnetic stimulators are
generally complex and expensive and use a high current impulse generator
that may produce discharge currents of 5,000 amps or more, which is
passed through the stimulator coil to produce a magnetic pulse. The
principles of electrical stimulation using a magnetic stimulator, along
with descriptions of medical applications of magnetic stimulation, are
reviewed in: Chris HOVEY and Reza Jalinous, The Guide to Magnetic
Stimulation, The Magstim Company Ltd, Spring Gardens, Whitland,
Carmarthenshire, SA34 OHR, United Kingdom, 2006.
SUMMARY
[0022] The present invention is concerned with devices and methods for the
treatment of a medical condition of a patient, in which treatment
involves the electrical stimulation of a selected nerve. In particular,
the devices and method of the present invention involve measuring a
physiological property of the patient (such as heart rate variability or
the like) and adjusting the signal delivered to the nerve based on that
property to optimize the signal and the treatment.
[0023] In one aspect of the in invention, a system for treating a medical
condition of a patient comprises a physiological sensor that produces a
physical output that is a measurement of a property of a physiological
entity or parameter of the patient and a stimulator configured to
generate one or more electrical impulses and to apply those electrical
impulses to a nerve at a target region in the patient's body. The signal
generator is configured to vary a property of the electrical impulses
based on the physiological entity or parameter to optimize the electrical
impulses and the treatment of the medical condition.
[0024] Typically, the sensors will include one or more electrodes applied
to the skin for measuring the patient's electrocardiogram (ECG), heart
rate variability, electromyogram (EMG), electroencephalogram (EEG),
and/or skin conductance and galvanic skin response. Another typical
sensor is a thermometer for measuring finger temperature and blood flow.
However, the invention contemplates the use of most any physiological
sensor, particularly ones that are used for ambulatory monitoring. The
properties of the electrical impulse that can be varied include the
frequency, amplitude (voltage or current), duty cycle and/or the duration
of the electrical impulse.
[0025] In certain embodiments, the system comprises software and hardware
components to fix the parameters of the electrical impulses after they
have been optimized. In one aspect, feedback provided by the
physiological sensor optimizes the signal applied to the nerve. Once the
signal has been optimized, the software and hardware components of the
system fix the electrical impulse based on the parameters that have been
sensed by the physiological sensor. The signal generator will then apply
the fixed electrical impulse to the patient.
[0026] In certain embodiments, methods are provided to apply an electrical
impulse to modulate, stimulate, inhibit or block electrical signals in
nerves within or around the carotid sheath, to acutely treat a condition
or symptom of a patient. In certain preferred embodiments, the electrical
signal may be adapted to reduce, stimulate, inhibit or block electrical
signals in a vagus nerve to treat many conditions, such as hypotension
associated with sepsis or anaphylaxis, hypertension, diabetes,
bronchoconstriction, hypovolemic shock, asthma, sepsis, epilepsy,
depression, obesity, gastroparesis, anxiety disorders, primary headaches,
such as migraines or cluster headache, Alzheimer's disease and any other
ailment affected by vagus nerve transmissions. Such conditions or
symptoms are described in co-pending, commonly assigned patent
applications listed in the section Cross Reference to Related
Applications, the complete disclosures of which have already been
incorporated herein by reference.
[0027] In one aspect of the invention, a stimulation device comprises one
or more electrodes and a pulse generator and is configured for
implantation at a target site adjacent to or near excitable tissue, such
as a nerve, within the patient's body. In certain embodiments, the power
source may also be implanted with the stimulation device or at another
location within the patient's body. In other embodiments, the energy that
is used to produce the impulses is received wirelessly by a dipole or
other type of antenna that is also part of the stimulator. The received
energy is preferably from far-field or approximately plane wave
electromagnetic waves in the frequency range of about 0.3 to 10 GHz, more
preferably about 800 MHz to 6 GHz and even more preferably about 800 MHz
to 1.2 GHz. In an exemplary embodiment, the carrier signal is around 915
MHz. The electrical energy is transmitted from the antenna of an external
energy source that is preferably a meter or more outside the patient, but
that may also be situated closer or even be placed within the patient. In
some embodiments, the transmitter may be worn around the neck as a
pendant, placed in a pocket, attached to a belt or watch, or clipped to
clothing.
[0028] In another aspect of the invention, the stimulator circuit
comprises either a battery or a storage device, such as a capacitor, for
storing energy or charge and then delivering that charge to the circuit
to enable the circuit to generate the electrical impulses and deliver
those impulses to the electrodes. The energy for the storage device is
preferably wirelessly transmitted to the stimulator circuit through a
carrier signal from the external controller. In the preferred
embodiments, the energy is delivered to the energy storage device between
electrical impulses. Thus, the energy is not being delivered in
"real-time", but during the periods when the pulse is not being delivered
to the nerve or during the refractory period of the nerve.
[0029] The electrical impulse is sufficient to modulate a selected nerve
(e.g., vagus or one of its branches) at or near the target region to
treat a condition or symptom of the patient. The stimulator is configured
to induce a peak pulse voltage sufficient to produce an electric field in
the vicinity of the nerve, to cause the nerve to depolarize and reach a
threshold for action potential propagation. By way of example, the
threshold electric field for stimulation of the nerve may be about 8 V/m
at 1000 Hz. For example, the device may produce an electric field within
the patient of about 10 to 600 V/m (preferably less than 100 V/m) and/or
an electrical field gradient of greater than 2 V/m/mm. Electric fields
that are produced at the vagus nerve are generally sufficient to excite
all myelinated A and B fibers, but not necessarily the unmyelinated C
fibers. However, by using a suitable amplitude of stimulation, excitation
of A-delta and B fibers may also be avoided.
[0030] The stimulation device may be implanted within a patient by open,
endoscopic or minimally invasive methods, In a preferred embodiment, the
stimulator is introduced through a percutaneous penetration in the
patient to a target location within, adjacent to, or in close proximity
with, the carotid sheath that contains a vagus nerve. Once in position,
electrical impulses are applied through the electrodes of the stimulator
to one or more selected nerves (e.g., vagus nerve or one of its branches)
to stimulate, block or otherwise modulate the nerve(s) and treat the
patient's condition or a symptom of that condition. For some conditions,
the treatment may be acute, meaning that the electrical impulse
immediately begins to interact with one or more nerves to produce a
response in the patient. In some cases, the electrical impulse will
produce a response in the nerve(s) to improve the patient's condition or
symptom in less than 3 hours, preferably less than 1 hour and more
preferably less than 15 minutes. For other conditions, intermittent
scheduled or as-needed stimulation of the nerve may produce improvements
in the patient over the course of several days or weeks.
[0031] In other embodiments, devices are disclosed that allow the
stimulation to be performed noninvasively, in which electrodes (and in
certain embodiments, magnetic coils) are placed against the skin of the
patient. In preferred embodiments of the invention, the selected nerve is
a vagus nerve that lies under the skin of the patient's neck. A more
complete description of such a device can be found in one of applicant's
co-pending patent applications referenced above.
[0032] In another aspect of the invention, one or more of the
physiological sensors may be used to perform biofeedback, in which output
from the sensor is used to generate a biofeedback signal that can be
experienced by at least one of the patient's exteroceptive sense organs
(time-varying audio signal, visual display, tactile signal, etc.). The
biofeedback signal is generally constructed to be proportional to the
sensor's output. The patient then voluntarily uses conscious awareness of
that biofeedback signal to mentally control a bodily function or
structure that modulates the amplitude of the physiological property that
is measured by the physiological sensor, thereby completing the
biofeedback loop. Control of a physiological property using biofeedback
is a learned skill, and many individuals are unable to learn to use
biofeedback to control particular physiological properties.
[0033] In the present invention, one preferred method of providing a
biofeedback signal to the patient is by electrically stimulating the skin
with a signal that varies according to the magnitude of the output of a
physiological sensor. The electrodes that stimulate the skin are the same
as the ones that may also be used to stimulate a large nerve that lies
deeper under the electrodes and skin, such as a vagus nerve.
[0034] Treating a medical condition may also be implemented automatically
(involuntarily) within the context of engineering control theory.
Physiological signals that are measured with sensors are presented as
input to a controller. The controller, comprising for example, the
disclosed nerve stimulator, a PID, and a feedback or feedforward model,
then provides input to the patient via stimulation of a vagus nerve. The
vagus nerve stimulation in turn modulates components of the patient's
nervous system, such as the autonomic nervous system, which results in
modulation of the physiological properties that are measured with
sensors, thereby completing the automatic control loop. The modulated
components of the patient's nervous system may include particular resting
state networks, such as the default mode network.
[0035] In another aspect of the invention, interoceptive representation
that is presented to--and is represented in--the brain's right anterior
insula and related structures, may be derived in part from artificial or
virtual signals that correspond to stimulation of fibers in the vagus
nerve, rather from the ordinary signaling of bodily interoceptors. The
patient may be conscious of the artificial interoception and may use it
to mentally control a bodily function or structure that modulates the
amplitude of the physiological property that is measured by the
physiological sensor. Thus, the invention contemplates a voluntary,
conscious response to the artificial interoception, even though it
originates from vagus nerve stimulation rather than from stimulation of
an exteroceptive sense as in biofeedback.
[0036] In the most general configuration of the disclosed devices and
methods, the three above-mentioned mechanisms (biofeedback, direct
stimulation of the vagus nerve to effect automatic control, and
artificial interoceptive sensation) will collectively modulate the target
physiological system, interacting with one another to determine the value
of the sensed physiological signal. Part of the interaction is determined
by the manner in which the nerve stimulator/biofeedback
device/physiological controller is programmed. For example, direct
stimulation of the physiological system via the vagus nerve may be
programmed to follow and amplify or enhance changes in the measured
sensor values that occur as a result of biofeedback. In other
embodiments, both biofeedback and vagus nerve stimulation are performed
simultaneously, and mathematical modeling is used to infer the
physiological effects that are due to the biofeedback, thereby allowing
the device to infer the conscious intentions of the patient and apply the
vagus nerve stimulation accordingly. For the subset of individuals who
are unable to control their physiological signals adequately using
biofeedback, even after multiple training attempts, and even with
amplification of biofeedback effects using vagus nerve stimulation as
indicated above, the device may also be programmed to use vagus nerve
stimulation alone to automatically perform the physiological control.
[0037] In a preferred embodiment of the invention, an electrical
stimulator housing comprises a source of electrical power and two or more
remote electrodes that are configured to stimulate the deep nerve, as
well as the skin if so desired. The stimulator may comprise two
electrodes that lie side-by-side, wherein the electrodes are separated by
electrically insulating material. Each electrode is in continuous contact
with an electrically conducting medium that extends from the
patient-interface element of the stimulator to the electrode. The
interface element contacts the patient's skin when the device is in
operation.
[0038] The system may also comprise a docking station that is used to
charge a rechargeable battery within the stimulator housing. The docking
station and stimulator housing may also transmit data to one another.
They may also transmit data to, and receive data from, a computer program
in a patient interface device, such as a mobile phone or nearby computer.
Physiological sensors may transmit their signals to the stimulator,
docking station, and/or interface device. Such data transmission is
preferably wireless, but wired communication between devices is also
contemplated.
[0039] For stimulation of the deep nerve, current passing through
electrodes of the stimulator may be about 0 to 40 mA, with voltage across
the electrodes of about 0 to 30 volts. The current is passed through the
electrodes in bursts of pulses. There may be 1 to 20 pulses per burst,
preferably five pulses. Each pulse within a burst has a duration of about
20 to 1000 microseconds, preferably 200 microseconds. A burst followed by
a silent inter-burst interval repeats at 1 to 5000 bursts per second
(bps, similar to Hz), preferably at 15-50 bps, and even more preferably
at 25 bps. The preferred shape of each pulse is a full sinusoidal wave.
[0040] The electrical stimulator is configured to induce a peak pulse
voltage sufficient to produce an electric field in the vicinity of a
nerve such as a vagus nerve, to cause the nerve to depolarize and reach a
threshold for action potential propagation. By way of example, the
threshold electric field for stimulation of the nerve may be about 8 V/m
at 1000 Hz. For example, the device may produce an electric field within
the patient of about 10 to 600 V/m (preferably less than 100 V/m) and an
electrical field gradient of greater than 2 V/m/mm. Electric fields that
are produced at the vagus nerve are generally sufficient to excite all
myelinated A and B fibers, but not necessarily the unmyelinated C fibers.
However, by using a reduced amplitude of stimulation, excitation of
A-delta and B fibers may also be avoided.
[0041] The preferred stimulator shapes an elongated electric field of
effect that can be oriented parallel to a long nerve, such as a vagus. By
selecting a suitable waveform to stimulate the nerve, along with suitable
parameters such as current, voltage, pulse width, pulses per burst,
inter-burst interval, etc., the stimulator produces a correspondingly
selective physiological response in an individual patient. Such a
suitable waveform and parameters are simultaneously selected to avoid
substantially stimulating nerves and tissue other than the target nerve,
avoiding the stimulation of nerves in the skin that produce pain, but
optionally stimulating receptors in the skin that may be used for
biofeedback purposes.
[0042] The novel systems, devices and methods for treating medical
conditions are more completely described in the following detailed
description of the invention, with reference to the drawings provided
herewith, and in claims appended hereto. Other aspects, features,
advantages, etc. will become apparent to one skilled in the art when the
description of the invention herein is taken in conjunction with the
accompanying drawings.
INCORPORATION BY REFERENCE
[0043] Hereby, all issued patents, published patent applications, and
non-patent publications that are mentioned in this specification are
herein incorporated by reference in their entirety for all purposes, to
the same extent as if each individual issued patent, published patent
application, or non-patent publication were specifically and individually
indicated to be incorporated by reference.
[0044] This application refers to the following patents and patent
applications: U.S. application Ser. No. 13/279,437, filed Oct. 24, 2011,
which published as U.S. 2012-0101326 on Apr. 26, 2012; U.S. application
Ser. No. 13/222,087, filed Aug. 31, 2011, which published as U.S.
2012-0029591 on Feb. 2, 2012; U.S. application Ser. No. 13/183,765, filed
Jul. 15, 2011, which published as U.S. 2011-0276112 on Nov. 10, 2011;
U.S. application Ser. No. 13/183,721, filed Jul. 15, 2011, which
published as U.S. 2011-0276107 on Nov. 10, 2011; U.S. application Ser.
No. 13/109,250, filed May 17, 2011, which published as U.S. 2011-0230701
on Sep. 22, 2011; U.S. application Ser. No. 13/075,746, filed Mar. 30,
2011, which published as U.S. 2011-0230938 on Sep. 22, 2011; U.S.
application Ser. No. 13/005,005, filed Jan. 12, 2011, which published as
U.S. 2011-0152967 on Jun. 23, 2011; U.S. application Ser. No. 12/964,050,
filed Dec. 9, 2010, which published as U.S. 2011-0125203 on May 26, 2011;
U.S. application Ser. No. 12/859,568, filed Aug. 19, 2010, which
published as U.S. 2011-0046432 on Feb. 24, 2011; U.S. application Ser.
No. 12/408,131, filed Mar. 20, 2009, which published as U.S. 2009-0187231
on Jul. 23, 2009; U.S. application Ser. No. 12/612,177, filed Nov. 4,
2009, now U.S. Pat. No. 8,041,428 issued Oct. 18, 2011; U.S. application
Ser. No. 12/859,568, filed Aug. 19, 2010, which published as U.S.
2011-0046432 on Feb. 24, 2011; U.S. application Ser. No. 13/208,425,
filed Aug. 12, 2011, which published as U.S. 2011-0319958 on Dec. 29,
2011; U.S. application Ser. No. 12/964,050, filed Dec. 9, 2010, which
published as U.S. 2011-0125203 on May 26, 2011; U.S. application Ser. No.
13/005,005, filed Jan. 12, 2011, which published as U.S. 2011-0152967 on
Jun. 23, 2011; U.S. application Ser. No. 13/024,727, filed Feb. 10, 2011,
which published as U.S. 2011-0190569 on Aug. 4, 2011; U.S. application
Ser. No. 13/075,746, filed Mar. 30, 2011, which published as U.S.
2011-0230938 on Sep. 22, 2011; U.S. application Ser. No. 13/109,250,
filed May 17, 2011, which published as U.S. 2011-0230701 on Sep. 22,
2011; U.S. application Ser. No. 13/183,721, filed Jul. 15, 2011, which
published as U.S. 2011-0276107 on Nov. 10, 2011; U.S. application Ser.
No. 13/222,087, filed Aug. 31, 2011, which published as U.S. 2012-0029591
on Feb. 2, 2012; U.S. application Ser. No. 13/357,010, filed Jan. 24,
2012, which published as U.S. 2012-0185020 on Jul. 19, 2002; U.S.
application Ser. No. 13/736,096, filed Jan. 8, 2013, which published as
U.S. 2013-0131746 on May 23, 2013; U.S. application Ser. No. 13/603,781,
filed Sep. 5, 2012, which published as U.S. 2013-0245711 on Sep. 19,
2013; U.S. application Ser. No. 13/671,859, filed Nov. 8, 2012, which
published as U.S. 2013-0066392 on Mar. 14, 2013; U.S. application Ser.
No. 13/731,035, filed Dec. 30, 2012, which published as U.S. 2013-0131753
on May 23, 2013; U.S. application Ser. No. 13/858,114, filed Apr. 8,
2013; and U.S. application Ser. No. 13/872,116, filed Apr. 29, 2013,
which published as U.S. 2013-0245486 on Sep. 19, 2013.
BRIEF DESCRIPTION OF THE DRAWINGS
[0045] For the purposes of illustrating the various aspects of the
invention, there are shown in the drawings forms that are presently
preferred, it being understood, however, that the invention is not
limited by or to the precise data, methodologies, arrangements and
instrumentalities shown, but rather only by the claims.
[0046] FIGS. 1A-1C provide schematic diagrams for the operation of: (FIG.
1A) a conventional closed-loop automatic physiological control system;
(FIG. 1B) a conventional biofeedback system; and (FIG. 1C) a closed loop
nerve stimulator and biofeedback device and/or automatic physiological
control system, respectively according to the present invention.
[0047] FIG. 2 shows a schematic view of nerve modulating devices according
to the present invention, which supply controlled pulses of electrical
current to body-surface electrodes.
[0048] FIGS. 3A-3C illustrate a front view, a back view and a docking
station for a dual-electrode stimulator according to an embodiment of the
present invention, which is shown to attach to a docking station.
[0049] FIGS. 4A and 4B show a cross sectional and expanded view,
respectively, of one of the stimulator heads that were shown in FIGS. 3A
and 3B.
[0050] FIGS. 5A-5D show some types of devices that may communicate with
the docking station and/or stimulator shown in FIG. 3C, comprising a
remote control (FIG. 5A), a mobile phone (FIG. 5B), a touchscreen device
(FIG. 5C), and a laptop computer (FIG. 5D).
[0051] FIG. 6 shows an expanded diagram of the control unit shown in FIG.
2, separating components of the control unit into those within the body
of the stimulator, those within the docking station, and those within
hand-held and internet-based devices, also showing communication paths
between such components.
[0052] FIG. 7 illustrates the approximate position of the housing of the
stimulator according one embodiment of the present invention, when used
to stimulate the right vagus nerve in the neck of an adult patient.
[0053] FIG. 8 illustrates the approximate position of the housing of the
stimulator according one embodiment of the present invention, when used
to stimulate the right vagus nerve in the neck of a child.
[0054] FIGS. 9A-9C illustrate the vertebrae and major vessels of the neck,
including vessels within the carotid sheath (FIG. 9A), as well as muscles
that lie in the vicinity of those vessels (FIGS. 9B and 9C).
[0055] FIG. 10 illustrates the housing of the stimulator according one
embodiment of the present invention, when positioned to stimulate a vagus
nerve in the patient's neck, wherein the stimulator is applied to the
surface of the neck in the vicinity of the identified anatomical
structures.
[0056] FIGS. 11A-11C show exemplary electrical voltage/current profiles
and waveforms for stimulating and/or modulating impulses that are applied
to a nerve.
[0057] FIG. 12 shows structures within a patient's nervous system that may
be modulated by electrical stimulation of a vagus nerve.
[0058] FIG. 13 shows functional networks within the brain (resting state
networks) that may be modulated by electrical stimulation of a vagus
nerve.
[0059] FIG. 14 illustrates the housing of the stimulator according one
embodiment of the present invention, when positioned to stimulate a
tibial nerve in the patient's ankle, in order to treat urinary
incontinence.
[0060] FIG. 15A is a schematic view of a nerve modulating system
(implantable lead module or electrical stimulator) according to one or
more aspects of the present invention.
[0061] FIG. 15B is a schematic view of an implantable stimulation device
according to the present invention.
[0062] FIG. 15C is a more specific view of the components of one
embodiment of the implantable stimulation device.
DETAILED DESCRIPTION
[0063] In the present invention, electrodes applied to the skin of the
patient generate electrical current or voltage impulses within tissue of
the patient. One of the objectives of the invention is to apply the
electrical impulses so as to interact with intrinsic signals of one or
more nerves, in order to achieve a therapeutic result, with or without
the simultaneous provision of a biofeedback signal to the patient. Much
of the disclosure will be directed specifically to treatment of a patient
by electrical stimulation in or around a vagus nerve, with devices
positioned non-invasively on or near a patient's neck. As recognized by
those having skill in the art, the methods should be carefully evaluated
prior to use in patients known to have preexisting cardiac issues. It
will also be appreciated that the devices and methods of the present
invention can be applied to other tissues and nerves of the body,
including but not limited to other parasympathetic nerves, sympathetic
nerves, spinal or cranial nerves. As a specific alternate example, the
devices may be positioned non-invasively on or near a patient's ankle, so
as to stimulate a tibial nerve there, in order to treat urinary
incontinence.
[0064] FIG. 1 illustrates a device according to the present invention
(FIG. 1C), contrasting it with other biomedical devices that make use of
feedback or biofeedback. FIG. 1A illustrates the operation of a
conventional prosthetic physiological control device. In that figure, a
physiological system has a physiological property that is transduced by a
physiological sensor. The output from that sensor serves as input to the
physiological control device. In turn, the control device generates a
control signal that is applied to the physiological system, so as to
control its function. For example, the physiological system could be the
patient's heart; the physiological sensors could be electrocardiographic
leads; the control device could be a cardiac pacemaker that determines
from the electrocardiographic signal whether the patient's heart-rate is
too low; and the control signal could be a current or voltage that is
applied to the heart's sinoatrial node when the heart-rate is too low (a
pacing signal).
[0065] The control device shown in FIG. 1A is intended to function even
when the patient is not conscious. In contrast, the biofeedback device
shown in FIG. 1B requires voluntary, conscious participation of the
patient. As shown there, a physiological system has a physiological
property that is transduced by a physiological sensor, and the output
from that sensor serves as input to the biofeedback device. The
biofeedback device does not generate a control signal that is applied
directly to the physiological system, but instead generates a biofeedback
signal that can be perceived by at least one of the patient's
exteroceptive sense organs (vision, hearing, touch, etc.). The perceived
signal reaches the patient's brain structures for conscious control,
which causes physiological responses that affect the physiological
system. As described in the background section of the present
application, the conscious responses are presumed to comprise an
emotional response that affects the physiological system and/or the
voluntary control of skeletal muscle. For example, the physiological
system could be a muscular motor unit; the physiological sensor could be
electromyographic leads situated above the motor unit on the patient's
skin; the biofeedback device could be designed to measure the magnitude
of the muscle activation on the basis of the electromyographic signal;
the biofeedback signal could be an audio tone that increases in amplitude
or frequency as the magnitude of the muscle activation increases; and the
brain structures for conscious action control would involve both auditory
and somatic nervous system components [BASMAJIAN J V. Control and
training of individual motor units. Science 141(3579, 1963):440-441]. As
described below, attempts have been made to consciously control many
different physiological systems using biofeedback, and many biofeedback
sensory modalities have been used other than an audio biofeedback signal.
[0066] Embodiments of devices of the present invention are illustrated in
FIG. 1C, which differ from the devices shown in FIGS. 1A and 1B in
several respects. As shown in FIG. 1C, a physiological system has a
physiological property that is transduced by a physiological sensor, and
the output from that sensor serves as input to the disclosed instrument
that is called a "nerve stimulator and biofeedback device and/or
physiological controller." For present purposes, the nerve stimulator
component of the instrument may be thought of as electrodes that are
applied to the patient's skin, along with associated electronic circuits
that cause electrical currents to flow through the electrodes and into
tissue under the electrodes.
[0067] The stimulator is configured to electrically stimulate a major
nerve noninvasively, such as the vagus nerve indicated in FIG. 1C. It may
also stimulate nerves within the skin that lie between the stimulator's
electrodes and vagus nerve, so that the patient may experience a tactile
or other cutaneous sensation. In fact, when the electrical stimulation is
relatively weak, a significant electrical stimulus may not even reach the
underlying vagus nerve, so that the patient experiences only tactile or
cutaneous sensations. In that case, only biofeedback signals to nerves
within the skin are used to control the physiological system, and the
instrument shown in FIG. 1C approximates the biofeedback device shown in
FIG. 1B. The electrical signals that simulate nerves within the skin may
be analog signals that vary in some continuous way relative to the
physiological property that is being transduced (e.g., heart rate, heart
rate variability (HRV), blood pressure, EEG, muscle unit activity, etc.).
Alternatively, the biofeedback signals may be digital, comprising
recognizable coded pulse trains, as has been suggested in connection with
tactile communication devices for the blind. For example,
electrocutaneous signals with three discrete intensity levels and three
discrete long-pulse durations can be discriminated [R. H. GIBSON.
Electrical stimulation of pain and touch. pp. 223-261. In: D. R.
Kenshalo, ed. The Skin Senses. Springfield, Ill.: Charles C Thomas, 1968;
Erich A. PFEIFFER. Electrical stimulation of sensory nerves with skin
electrodes for research, diagnosis, communication and behavioral
conditioning: A survey. Medical and Biological Engineering. 6(6,
1968):637-651; Alejandro HERNANDEZ-ARIETA, Hiroshi Yokoi, Takashi
Ohnishi, Tamio Arai. An f-MRI study of an EMG Prosthetic Hand Biofeedback
System. In: T. Arai et al. (Eds.). IAS-9, Proceedings of the 9th
International Conference on Intelligent Autonomous Systems, University of
Tokyo, Tokyo, Japan, Mar. 7-9, 2006, Amsterdam: IOS Press, 2006, pp.
921-929; Kahori KITA, Kotaro Takeda, Rieko Osu, Sachiko Sakata, Yohei
Otaka, Junichi Ushiba. A Sensory feedback system utilizing cutaneous
electrical stimulation for stroke patients with sensory loss. Proc. 2011
IEEE International Conference on Rehabilitation Robotics, Zurich,
Switzerland, Jun. 29-Jul. 1, 2011, 2011:5975489, pp 1-6]. It is
understood that although the biofeedback component of FIG. 1C may be
configured to use only electrical stimulation of the skin, the system may
be configured to use additional sensory modalities as well, such as audio
or visual biofeedback signals.
[0068] More generally, the instrument shown in FIG. 1C will directly
stimulate the vagus nerve, in addition to sensory nerves within the skin.
It is understood that the cutaneous stimulation described above may also
stimulate the vagus nerve through indirect mechanisms, especially in
infants, but such indirect stimulation of the vagus nerve is considered
to play at most only a minor role in the present invention [Tiffany FIELD
and Miguel Diego. Vagal activity, early growth and emotional development.
Infant Behav Dev 31(3, 2008): 361-373]. As described below and in
co-pending, commonly assigned patent application U.S. Ser. No.
13/222,087, entitled Devices and methods for non-invasive capacitive
electrical stimulation and their use for vagus nerve stimulation on the
neck of a patient, to SIMON et al. (which is hereby incorporated by
reference), Applicant has developed a stimulator device that can
noninvasively stimulate a vagus nerve directly in the patient's neck,
without producing cutaneous discomfort to a patient. When the vagus nerve
is being stimulated by the device, the quality of sensation in the
patient's skin above the vagus nerve depends strongly on the stimulation
current and frequency, such that when the currents are not much greater
than the perception threshold, the cutaneous sensations may be described
as tingle, itch, vibration, buzz, touch, pressure, or pinch. For
situations in which the skin is being stimulated with a constant current
and with a particular type of stimulation waveform that is described
below, any such cutaneous sensation may be ignored by the patient, and
the stimulator does not serve as a biofeedback device. In that case, the
device resembles instead the physiological control device shown in FIG.
1A. For example, the physiological system could be the patient's heart;
the physiological sensors could be electrocardiographic leads; the nerve
stimulator & physiological control device could determine from the
electrocardiographic signal whether the patient's heart-rate exhibits
tachycardia; and the signal applied to the vagus nerve could produce a
physiological response that reduces the heart-rate, by stimulating vagal
parasympathetic efferent nerves [Hendrik P. BUSCHMAN, Corstiaan J. Storm,
Dirk J. Duncker, Pieter D. Verdouw, Hans E. van der Aa, Peter van der
Kemp. Heart rate control via vagus nerve stimulation. Neuromodulation
9(3, 2006): 214-220; Japanese patent application JP2008/081479A
(publication JP2009233024A) with a filing date of Mar. 26, 2008, entitled
Vagus Nerve Stimulation System, to Fukui YOSHIHOTO].
[0069] Although the configuration described in the previous paragraph does
not make use of a cutaneous biofeedback signal, in some embodiments, the
patient may nevertheless become conscious of the stimulation of the vagus
nerve, as an artificial interoceptive sensation. Interoceptive sensations
from the body's interoceptors are conveyed to, and represented in, the
brain's right anterior insula and related structures, at which locations
the individual may be conscious of interoceptive activity. As described
below, some of the neural pathways leading to the insula involve afferent
fibers of the vagus nerve. Interoceptors within the body may convey
naturally-occurring interoceptive signals via vagal afferent fibers, but
in the present invention, electrical stimulation of the vagus nerve may
also produce artificial interoceptive signals. Thus, the present
invention contemplates the stimulation of vagal afferent fibers in such a
way that the patient may sense the stimulation as an internal bodily
signal, even though the signals are not produced by interoceptors. When
the artificial interoceptive signals are varied by the nerve stimulator
as a function of the output of a physiological sensor, the individual may
consciously respond to the artificial interoceptive signals as though
they were a biofeedback signal. This is despite the fact that the signals
are not biofeedback signals, because they are not presented to an
exteroceptive sense.
[0070] In a more general configuration of the system shown in FIG. 1C, a
cutaneous biofeedback signal may be superimposed upon the electrical
stimulation waveform that preferentially stimulates the vagus nerve
directly. Thus, in addition to the mechanisms described in the previous
two paragraphs, the stimulation waveform may also contain a time-varying
signal with frequency components that are designed specifically to
stimulate cutaneous nerves. The biofeedback signal will vary as a
function of the physiological parameter that is being sensed by the
physiological sensor (e.g., heart rate, skin conductance level, finger
temperature/blood flow, etc.). The biofeedback signal may be a continuous
analog signal, or it may be a digital signal, e.g., with three discrete
intensity levels and three discrete long-pulse durations that can be
discriminated. The patient may then consciously respond to the
biofeedback signal, for example, by relaxing or tensing skeletal muscles
or by eliciting a relaxing or agitated emotional response, thereby
modulating the tone of the sympathetic nervous system [COSTA F, Biaggioni
I. Role of adenosine in the sympathetic activation produced by isometric
exercise in humans. J Clin Invest. 93(1994):1654-1660; KREIBIG SD.
Autonomic nervous system activity in emotion: a review. Biol Psychol 84
(3, 2010):394-421].
[0071] The three mechanisms shown in FIG. 1C (biofeedback, artificial
interoceptive sensation, and direct stimulation via the vagus nerve) will
collectively modulate the physiological system, interacting with one
another to determine the value of the sensed physiological signal. Part
of the interaction is determined by the manner in which the nerve
stimulator/biofeedback device/physiological controller is programmed. For
example, direct stimulation of the physiological system via the vagus
nerve may be programmed to follow and amplify or enhance changes that
occur as a result of biofeedback. An embodiment of that example would
occur when the individual uses galvanic skin response biofeedback alone
to consciously reduce sympathetic tone through muscular and emotional
modulation, whereupon the device in FIG. 1C senses that reduction through
its programming and then amplifies the effect by increasing
parasympathetic tone after a brief time delay, by directly stimulating
vagal parasympathetic efferent nerve fibers.
[0072] As another example, the patient may be using heart rate variability
biofeedback alone to increase the amplitude of his or her respiratory
sinus arrhythmia, whereupon the device senses that increase and then
amplifies the effect by increasing parasympathetic tone after a brief
time delay, by directly stimulating vagal parasympathetic efferent nerve
fibers. In those examples, it is clear what the biofeedback effect is
initially, and the vagus stimulation is only applied thereafter to
amplify it. In other embodiments that are disclosed herein, both
biofeedback and vagus nerve stimulation are performed simultaneously, and
mathematical modeling is used to infer the effects that are due to the
biofeedback, thereby allowing the device to also infer the intentions of
the individual and apply the vagus nerve stimulation accordingly.
Consequently, the whole device (FIG. 1C) has more functionality than its
individual parts simply added together (e.g., FIG. 1A plus FIG. 1B).
Furthermore, because the physiological system is stimulated directly via
the vagus nerve, the present invention teaches methods and devices that
actually enable individuals to directly and voluntarily control visceral
autonomic functions via the vagus nerve, which is a long-felt but unmet
need, according to the information provided in the background section of
the present application. For the subset of individuals who are unable to
control their physiological signals adequately using biofeedback, even
after multiple training attempts, and even with enhancement of the
biofeedback effects using vagus nerve stimulation as described above, the
device shown in FIG. 1C may also be programmed to use vagus nerve
stimulation alone to perform the control automatically.
[0073] In certain embodiments, the system comprises software and hardware
components to fix the parameters of the electrical impulses after they
have been optimized. In one aspect, feedback provided by the
physiological sensor optimizes the signal applied to the nerve. Once the
signal has been optimized, the software and hardware components of the
system fix the electrical impulse based on the parameters that have been
sensed by the physiological sensor. The signal generator will then apply
the fixed electrical impulse to the patient. For example, the physician
may be able to optimize the electrical impulse in the hospital or office
setting by applying electrical impulses and measuring their effect on
certain body parameters. The impulses can then be varied either manually
or automatically until the effect is optimized. If the stimulator is
implanted, the signal generator may automatically apply the optimized
electrical impulse to the patient at certain times throughout the day, or
it may be designed to only apply the electrical impulses when activated
by the patient. If the stimulator is a non-invasive device, the patient
self-treats and applies the optimized electrical impulses according to
the treatment algorithm set up by the physician.
[0074] FIG. 1C shows that the combined nerve stimulator/biofeedback
device/physiological controller may also receive environmental signals as
input. For example, if the device is being used to treat a patient with
migraine headache, it may be useful to include ambient light and ambient
sound as input, as measured with a photo-detector and a microphone,
because excessive sound and light can provoke or exacerbate a migraine
attack. If the device is being used to treat asthma, it may be useful to
include environmental signals related to air quality as input. Such
environmental input was previously disclosed for noninvasive vagus nerve
stimulation devices in co-pending, commonly assigned patent application
U.S. Ser. No. 13/655,716, entitled Nerve stimulation methods for averting
imminent onset or episode of a disease, to SIMON et al., as well as in
other applications cited in the Cross-Reference to Related Applications.
Such earlier-disclosed devices and methods are adapted here to include
the use of biofeedback.
[0075] There is little prior art involving both vagus nerve stimulation
and biofeedback devices, where the term "biofeedback device" means here
essentially what is defined in 21 CFR 882.5050: "a biofeedback device is
an instrument that provides a visual or auditory signal [or other such
exteroceptive signal] corresponding to the status of one or more of a
patient's physiological parameters (e.g., brain alpha wave activity,
muscle activity, skin temperature, etc.) so that the patient can control
voluntarily these physiological parameters . . . . " The term biofeedback
appears in the text of some patents or patent applications, but often
with a different meaning than what is meant here. Examples of such
different usages of the term are as follows. U.S. Pat. No. 7,657,310,
entitled Treatment of reproductive endocrine disorders by vagus nerve
stimulation, to BURAS, uses the term biofeedback to refer to feedback of
a signal that has been transduced from a patient's body, but not
voluntary mental control over such a signal. U.S. Pat. No. 8,509,902,
entitled Medical device to provide breathing therapy, to CHO et al.,
discloses devices and methods that are said to involve biofeedback, but
in fact, their invention is not concerned with voluntary control over a
biofeedback signal because it "relates generally to the use of diaphragm
contraction prolongation during breathing therapy sessions (e.g., when a
patient is not cognitive of respiratory control, such as when they are
sleeping) . . . . " U.S. Pat. No. 7,946,976, entitled Methods and devices
for the surgical creation of satiety and biofeedback pathways, to
GERTNER, uses the term biofeedback to mean an internal bodily control
signal, not the voluntary control over a biofeedback signal derived from
a physiological measurement. Patent application US20050149142, entitled
Gastric stimulation responsive to sensing feedback, to STARKEBAUM, uses
the term biofeedback to mean artificially-produced symptoms of
gastroparesis that are caused by electrical stimulation of the stomach.
[0076] However, some patents or patent applications do use the term
biofeedback in the sense that is intended here and also mention vagus
nerve stimulation. Application US 20120071731, entitled System and method
for physiological monitoring, to GOTTESMAN, describes the use of a
physiological sensor that can be used in a biofeedback application and
that can also be used to determine when to stimulate a vagus nerve.
However, the biofeedback and vagus nerve stimulation uses of the sensor
are described as being different applications. Similarly, U.S. Pat. No.
8,036,736, entitled Implantable systems and methods for identifying a
contraictal condition in a subject, to SNYDER et al., is concerned with
the analysis of physiological signals for purposes of automatic
identification of circumstances under when an epilepsy patient should
undertake therapy. SNYDER mentions vagus nerve stimulation and
biofeedback techniques as two such alternative therapies, but not as
methods that should be performed together.
[0077] Patent application US 20100004705, entitled Systems, Methods and
devices for treating tinnitus, to KILGARD et al. and US 20100003656,
entitled Systems, methods and devices for paired plasticity, to KILGARD
et al, also apparently use the term biofeedback in the sense that is
intended here. They describe the simultaneous use of electrical neural
stimulation with biofeedback therapy (among other therapies), including
the use of invasive vagus nerve stimulation. However, according to
KILGARD et al., the disclosed relation between the biofeedback therapy
and neural stimulation relates only to their mutual timing. There is
nothing in their application to suggest that the actual parameters of the
nerve stimulation are to be modulated in conjunction with the strength of
the biofeedback signal itself or of the physiological signal that serves
as the basis of the biofeedback signal. Furthermore, in that patent
application, the electrical stimulation and biofeedback signals are
described as being distinct entities, wherein the electrical stimulation
is shown in the figures there to be an invasive procedure, and
biofeedback is generally understood to be a noninvasive procedure. This
is in contrast to the present invention, in which the electrical
stimulation itself may comprise the biofeedback signal, and in which both
the electrical nerve stimulation and biofeedback methods are noninvasive
procedures. Also, according to KILGARD et al, the electrical stimulation
is said to induce plasticity in the brain, e.g., via activation of the
nucleus basalis, locus coeruleus, or amygdala, thereby enhancing efficacy
of the biofeedback therapy. However, the present invention does not
necessarily involve neuronal plasticity, and the present invention may
also produce stimulation of the nucleus basalis, locus coeruleus,
amygdala, and many other brain components, without inducing plasticity.
[0078] Description of the Nerve Stimulating/Modulating Devices
[0079] Devices of the present invention are able to stimulate a vagus
nerve, as well as the skin above the nerve, as now described. One
preferred embodiment of the present invention is shown in FIGS. 15A-15C.
[0080] As ordinarily practiced, the electrodes used to stimulate a vagus
nerve are implanted about the nerve during open neck surgery. For many
patients, this may be done with the objective of implanting permanent
electrodes to treat epilepsy, depression, or other conditions [Arun Paul
AMAR, Michael L. Levy, Charles Y. Liu and Michael L. J. Apuzzo. Chapter
50. Vagus nerve stimulation. pp. 625-638, particularly 634-635. In:
Elliot S. Krames, P. Hunber Peckham, Ali R. Rezai, eds. Neuromodulation.
London: Academic Press, 2009; KIRSE D J, Werle A H, Murphy J V, Eyen T P,
Bruegger D E, Hornig G W, Torkelson R D. Vagus nerve stimulator
implantation in children. Arch Otolaryngol Head Neck Surg 128(11,
2002):1263-1268]. In that case, the electrode is often a spiral
electrode, although other designs may be used as well [U.S. Pat. No.
4,979,511, entitled Strain relief tether for implantable electrode, to
TERRY, Jr.; U.S. Pat. No. 5,095,905, entitled Implantable neural
electrode, to KLEPINSKI]. In other patients, a vagus nerve is
electrically stimulated during open-neck thyroid surgery in order to
confirm that the nerve has not been accidentally damaged during the
surgery. In that case, a vagus nerve in the neck is surgically exposed,
and a temporary stimulation electrode is clipped about the nerve
[SCHNEIDER R, Randolph G W, Sekulla C, Phelan E, Thanh P N, Bucher M,
Machens A, Dralle H, Lorenz K. Continuous intraoperative vagus nerve
stimulation for identification of imminent recurrent laryngeal nerve
injury. Head Neck. 2012 Nov. 20. doi: 10.1002/hed.23187 (Epub ahead of
print, pp. 1-8)].
[0081] In a commonly assigned, copending application, Applicant disclosed
that it is also possible to electrically stimulate a vagus nerve using a
minimally invasive surgical approach, namely percutaneous nerve
stimulation. In that procedure, a pair of electrodes (an active and a
return electrode) are introduced through the skin of a patient's neck to
the vicinity of a vagus nerve, and wires connected to the electrodes
extend out of the patient's skin to a pulse generator [Publication number
US20100241188, entitled Percutaneous electrical treatment of tissue, to
J. P. ERRICO et al.; SEPULVEDA P, Bohill G, Hoffmann T J. Treatment of
asthmatic bronchoconstriction by percutaneous low voltage vagal nerve
stimulation: case report. Internet J Asthma Allergy Immunol 7(2009):e1
(pp 1-6); MINER, J. R., Lewis, L. M., Mosnaim, G. S., Varon, J.,
Theodoro, D. Hoffman, T. J. Feasibility of percutaneous vagus nerve
stimulation for the treatment of acute asthma exacerbations. Acad Emerg
Med 2012; 19: 421-429].
[0082] Percutaneous nerve stimulation procedures had previously been
described primarily for the treatment of pain, but not for a vagus nerve,
which is ordinarily not considered to produce pain and which presents
special challenges [HUNTOON M A, Hoelzer B C, Burgher A H, Hurdle M F,
Huntoon E A. Feasibility of ultrasound-guided percutaneous placement of
peripheral nerve stimulation electrodes and anchoring during simulated
movement: part two, upper extremity. Reg Anesth Pain Med 33(6,
2008):558-565; CHAN I, Brown A R, Park K, Winfree C J. Ultrasound-guided,
percutaneous peripheral nerve stimulation: technical note. Neurosurgery
67 (3 Suppl Operative, 2010):ons136-139; MONTI E. Peripheral nerve
stimulation: a percutaneous minimally invasive approach. Neuromodulation
7(3, 2004):193-196; Konstantin V SLAVIN. Peripheral nerve stimulation for
neuropathic pain. US Neurology 7(2, 2011):144-148].
[0083] In the present invention, electrodes are preferably also introduced
percutaneously to the vicinity of a vagus nerve, but unlike the previous
minimally invasive disclosure, the electrodes are not ultimately
connected to wires that extend outside the patient's skin. Instead, in
the present invention, the percutaneously implanted stimulator receives
energy wirelessly from an external transmitter that need not be in close
proximity to the skin of the patient, and electrical pulse generation
occurs within the implanted stimulator using that energy.
[0084] As shown in FIG. 15A, the nerve modulating device 300 of the
present invention (also known as an implantable lead module or simply an
electrical nerve stimulator) is powered by the receipt of far-field or
approximately plane wave electromagnetic energy with frequencies in the
range of 0.3 to 10 GHz (preferably about 800 MHz to about 6 GHz, and more
preferably about 800 MHz to about 1.2 MHz) which is received wirelessly
by an antenna 360 within, or attached to, the device 300. The energy that
powers the nerve modulating device 300 is transmitted by an external
device, which in FIG. 15A is labeled as a Controller 370. Controller 370
is in turn controlled by a programmer device 380, which preferably
communicates with controller 370 wirelessly. In operation, the nerve
modulating device 300 is implanted within the patient, the controller 370
may be either outside of the patient or implanted within the patient, and
the programmer 380 is operated manually by the patient or a caregiver.
The antenna of the controller 370 is actively tuned/matched to the
resonant frequency of an antenna in the implanted device 300 so that the
maximum efficiency of power transmission is achieved. There may be
several antennae at various orientations in the external unit and/or in
the implanted signal generator to enhance coupling efficiency in various
orientations. The unit 370 supplying power and control to the implanted
device 300 could be AC powered and/or battery powered. If powered by
rechargeable batteries, a battery charger may be an accessory to the
system. The controller 370 is preferably both portable and rechargeable.
In one embodiment, it may be worn around the neck as a pendant, placed in
a pocket, or clipped to clothing. This wireless transmitter 370 is
preferably recharged at a recharging base and has a significant range of
transmission, preferably up to four feet, so that patients can sleep
without having to wear the transmitter.
[0085] FIG. 15B is a more detailed schematic diagram of the nerve
modulating device 300 for delivering electrical impulses to nerves. As
shown, device 300 comprises an electrical impulse generator 310; a power
source 320 coupled to the electrical impulse generator 310; a control
unit 330 in communication with the electrical impulse generator 310 and
coupled to the power source 320; and one or more electrodes 340 coupled
to the electrical impulse generator 310. Nerve modulating device 300 is
configured to generate electrical impulses sufficient to modulate the
activity of one or more selected regions of a nerve (not shown). The
power source 320 receives energy wirelessly via an antenna 360, wherein
the energy is in the form of far-field or approximately plane-wave
electromagnetic waves with frequencies in the range of 0.3 to 10 GHz,
preferably about 800 MHz to about 1.2 MHz.
[0086] The control unit 330 may control the electrical impulse generator
310 for generation of a signal suitable for amelioration of a patient's
condition when the signal is applied via the electrodes 340 to the nerve.
It is noted that nerve modulating device 300 excluding the electrodes 340
may be referred to by its function as a pulse generator. U.S. Patent
Application Publications 2005/0075701 and 2005/0075702, both to SHAFER,
both of which are incorporated herein by reference, relating to
stimulation of neurons of the sympathetic nervous system to attenuate an
immune response, contain descriptions of pulse generators that may be
applicable to various embodiments of the present invention.
[0087] FIG. 15C illustrates one embodiment of the nerve modulating device
300 that consumes relatively little power and may therefore receive power
from a correspondingly weak and/or distant external transmitter. To
achieve low power consumption, the embodiment is designed to use a
minimum of components. This may be accomplished by designing the device
to produce constant voltage pulses, rather than constant current pulses,
because circuits for the latter are more complex and consume more power
than the former. However, for some patients a constant current pulse may
be preferred, depending on the detailed anatomy of the patient's neck in
the vicinity of the stimulated nerve (see below). Consequently, constant
current pulses are also contemplated by the invention [DELIMA, J. A. and
Cordeiro, A. S. A simple constant-current neural stimulator with accurate
pulse-amplitude control. Engineering in Medicine and Biology Society,
2001. Proceedings of the 23rd Annual International Conference of the IEEE
(Vol. 2, 2001) 1328-1331]. In either case, simplicity of circuit design
is provided by a design that makes the amplitude of the pulse constant,
rather than by allowing the amplitude to be variable. Accordingly, the
present invention modulates the stimulation power to the nerve by
altering the number and timing of the pulses, rather than by modulating
the amplitude of individual pulses. Additional simplicity of design may
be achieved by using communication that occurs in one direction only,
from the transmitter to the stimulator (simplex communication according
to the ANSI definition, rather than half or full duplex communication).
[0088] The stimulator circuit is novel in that it removes one (or more)
elements from conventional stimulators, without sacrificing performance.
In particular, the present invention removes from conventional designs
the ability of the stimulator to vary the amplitude of the stimulation
pulses. Unexpectedly, one can get substantially the same stimulatory
effect as that provided by conventional stimulators, by keeping waveform
parameters fixed, particularly the amplitude of pulses, but by then
controlling the number and timing of pulses that the nerve experiences,
in order to achieve the same physiologically desirable level of nerve
stimulation. In essence, this invention uses an adjustable number of
fixed voltage (or fixed current) pulses with fixed duration to elicit
desired changes in nerve response. These fixed voltage pulses create one
long continuous pulse to the nerve to ensure that sufficient energy is
delivered to the nerve to cause the nerve to reach its action potential
and fire. Thus, the present invention reaches the threshold energy level
for a nerve to fire by adjusting the duration of the pulse received by
the nerve, rather than adjusting the amplitude of the pulse.
[0089] In another aspect of the invention, the specific number of fixed
amplitude pulses that will be delivered to the nerve is preferably
determined through an iterative process with each patient. Once the
surgeon determines the number of fixed voltage pulses required to
stimulate the nerve for a particular patient, this number is programmed
into either the external controller or the implantable stimulator.
[0090] A constant-voltage pulse design teaches against prevailing
preferred designs for vagus nerve stimulators. Thus, constant-voltage
pulses are used in cardiac pacemakers, deep brain stimulation, and some
implantable neuromodulators for treatment of incontinence and chronic
pain, but constant-current pulses are used for cochlear implants and
vagus nerve stimulators [D. PRUTCHI and M. Norris Stimulation of
excitable tissues. Chapter 7, pp. 305-368. In: Design and development of
medical electronic instrumentation. Hoboken: John Wiley & Sons, 2005]. In
the latter applications, the constant current design is said to be
preferred because slight variations in stimulator-to-nerve distance
change the ability of the constant-voltage pulse stimulator to depolarize
the nerve, which is less of a problem with constant-current pulse
stimulators. With the constant current design, the stimulation thresholds
stay more or less constant even with changing electrode impedance and
ingrowth of tissue into the neural interface [Emarit RANU. Electronics.
Chapter 10, pp. 213-243. In: Jeffrey E. Arle, Jay L. Shils (eds).
Essential Neuromodulation. Amsterdam, Boston: Academic Press. 2011]. For
example, the BION stimulators described in the background section of the
present application generate only constant current pulses.
[0091] In some embodiments of the present invention, a constant voltage
pulse is used because it can be produced with a simpler circuit that
consumes less power, as compared with constant pulse current circuits.
The above-mentioned potential problem with variation in
stimulator-to-nerve distance is addressed by anchoring the stimulator to
the vagus nerve. Furthermore, the problem may be circumvented to some
extent in the present invention by coating the stimulator's electrodes
with a very thin layer of poorly conducting material. This is because the
presence of a poorly conducting boundary layer surrounding the stimulator
minimizes the differential effects of conductivity variations and
electrode location during constant current and constant voltage
stimulation [Mark M. STECKER. Nerve stimulation with an electrode of
finite size: differences between constant current and constant voltage
stimulation. Computers in Biology and Medicine 34(2004):51-94].
[0092] Additional circuit simplicity and minimized power requirements are
accomplished in the embodiment shown in FIG. 15C by fixing the
characteristics of the stimulation pulses, rather than by adding circuits
that would allow the characteristics to be adjusted through use of
external control signals. For example, the output pulses shown in FIG.
15C are shown to be generated using a pair of monostable multivibrators.
The first multivibrator receives a trigger pulse from the control unit
330, resulting in a pulse of fixed duration. The second multivibrator is
triggered by the falling edge of the first multivibrator's pulse, and the
pair of pulses from the two multivibrators are combined with suitable
polarity using a differential operational amplifier. Thus, in this
example, the impulse generator 310 consists of the multivibrators and
operational amplifier. The amplifier in turn presents the stimulation
pulses to the electrodes 340. The time period that a monostable
multivibrator remains in its unstable state (the pulse width) is a
function of its component resistor and capacitor values, so if the pulse
width can be preselected for a patient, the device can be designed using
correspondingly fixed R and C values. On the other hand, if a variable
pulse width is needed during preliminary testing with a patient, the
multivibrator circuit can be made more complex, with the pulse width
selected on the basis of coded signals that are transmitted to the
impulse generator 310 via the control unit 330. Once the appropriate
pulse width has been selected, a control signal may be sent from the
control unit 330 to disable extraneous power consumption by the variable
pulse-width circuitry. Proper pulse width is particularly important in
stimulating nerve fibers having the appropriate diameters [see discussion
below and SZLAVIK R B, de Bruin H. The effect of stimulus current pulse
width on nerve fiber size recruitment patterns. Med Eng Phys 21(6-7,
1999):507-515].
[0093] It is also understood that more complex pulses may also be
preferred, which would require a correspondingly more complex circuitry
and possibly additional power consumption, as compared with the circuit
shown in FIG. 15C [JEZERNIK S, Morari M. Energy-optimal electrical
excitation of nerve fibers. IEEE Trans Biomed Eng 52(4, 2005):740-743;
Wongsarnpigoon A, Woock J P, Grill W M. Efficiency analysis of waveform
shape for electrical excitation of nerve fibers. IEEE Trans Neural Syst
Rehabil Eng 18(3, 2010):319-328; FOUTZ T J, Ackermann D M Jr, Kilgore K
L, McIntyre C C (2012) Energy efficient neural stimulation: coupling
circuit design and membrane biophysics. PLoSONE 7(12): e51901.
doi:10.1371/journal.pone.0051901, pp. 1-8; McLEOD K J, Lovely D F, Scott
R N. A biphasic pulse burst generator for afferent nerve stimulation. Med
Biol Eng Comput 25(1, 1987):77-80].
[0094] The control unit 330 in FIG. 15C is shown to exercise its control
only by presenting trigger pulses to the impulse generator 310. In this
example, the train of pulses appearing across the electrodes 340 is
determined only by the timing of the sequence of trigger pulses. The
trigger pulses are themselves encoded in the signal that is transmitted
from controller 370 in FIG. 15A, shown in FIG. 15C as "RF signal with
encoded trigger pulse." The trigger pulses are extracted and
reconstructed from the transmitted signal by an RF demodulator in the
control unit 330. There are many methods for transmitting and decoding
such control signals, and the present invention may be designed to use
any of them [Robert PUERS and Jef Thone. Short distance wireless
communications. Chapter 7, pp. 219-277, In: H.-J. Yoo, C. van Hoof
(eds.), Bio-Medical CMOS ICs. New York: Springer, 2011]. Because the
timing of pulses is determined by the trigger pulses emanating from the
transmitted signal, the circuit shown in FIG. 1C does not even need a
clock, thereby reducing its power requirements. However, in other
embodiments a clock may be included as part of the timing circuitry. It
is understood that in order to command a pulse of the treatment signal
and switch that pulse to the electrodes, it is possible to use a control
RF signal having a different frequency than the one used to provide
power, or encode the command based on variation in the RF signal's
amplitude, pulse width and/or duration.
[0095] The transmitted RF signal is received by an antenna 360, and the
signal provides power for the stimulation device 300, in addition to the
control signals. The power is provided by the power source 320 in FIG.
15C. As shown there, energy from the transmitted RF signal (beamed power)
is accumulated in a storage capacitor, which is eventually discharged in
conjunction with the creation of stimulation pulses that are applied to
the electrodes 340. In addition to the beamed power, there may also be
scavenged power, which arises from the reception of ambient
electromagnetic radiation by the antenna 360. Special circuits and
antennas may be used to scavenge such ambient electromagnetic radiation
[Soheil RADIOM, Majid Baghaei-Nejad, Guy Vandenbosch, Li-Rong Zheng,
Georges Gielen. Far-field RF Powering System for RFID and Implantable
Devices with Monolithically Integrated On-Chip Antenna. In: Proc. Radio
Frequency Integrated Circuits Symposium (RFIC), 2010 IEEE, Anaheim,
Calif., 23-25 May 2010, pp. 113-116]. Power scavenging may be most
appropriate in a hospital setting where there is significant ambient
electromagnetic radiation, due to the use there of diathermy units and
the like [FLODERUS B, Stenlund C, Carlgren F. Occupational exposures to
high frequency electromagnetic fields in the intermediate range (>300
Hz-10 MHz). Bioelectromagnetics 23(8, 2002):568-577].
[0096] The stimulator circuit comprises either a battery or a storage
device, such as a capacitor, for storing energy or charge and then
delivering that charge to the circuit to enable the circuit to generate
the electrical impulses and deliver those impulses to the electrodes. The
energy for the storage device is preferably wirelessly transmitted to the
stimulator circuit through a carrier signal from the external controller.
In the preferred embodiments, the energy is delivered to the energy
storage device between electrical impulses. Thus, the energy is not being
delivered in "real-time", but during the periods when the pulse is not
being delivered to the nerve or during the refractory period of the
nerve. For example, a typical electrical impulse may be ON for about 200
uS and then OFF for about 39,000 uS. The energy is delivered during this
longer OFF time, which enables the system to use a much smaller signal
from the external generator. The external generator delivers the carrier
signal over the OFF period to charge the energy storage device, which
then releases this energy or charge to the remainder of the circuit to
deliver the electrical impulse during the 200 uS ON time.
[0097] Transmitting energy to the storage device in between the electrical
impulses provides a number of advantages. First, it increases the length
of time that the electrical energy can be delivered to charge the storage
device. This reduces the strength of the signal required to deliver the
electrical energy to the storage device, thereby reducing the overall
power requirements of the external controller and reducing the complexity
of the stimulator circuirtry. In addition, it enhances the safety of the
device because it reduces the risk that uncontrolled environmental RF
energy will create an electrical connection between the nerve and the
charged energy. Since the storage device is receiving electrical energy
between electrical impulses, there is no electrical connection between
the stimulator circuit and the nerve as the storage device is charged.
This reduces the risk of the electrical energy being accidently applied
to the nerve.
[0098] In order to power the impulse generator and demodulation circuits,
the power source 320 in FIG. 15C makes use of a voltage regulator, the
output from which is a stable voltage V. The circuits that may be
selected for the voltage regulator comprise those described by BOYLESTAD
[Robert L BOYLESTAD and Louis Nashelsky. Power Supplies (Voltage
Regulators). Chapter 18, pp. 859-888. In: Electronic devices and circuit
theory, 8th ed. Upper Saddle River, N.J.: Prentice Hall, 2002].
[0099] In preferred embodiments of the present invention, the parameters
of fixed stimulation pulses are generally as follows. The shape of the
pulse is square, sine, triangular or trapezoidal with negative voltage
return to eliminate DC bias. The electrical impulse will typically have a
frequency of between about 1-500 Hz, preferably about 1 to 50 Hz, and
more preferably about 10-35 Hz. In an exemplary embodiment, the frequency
for the impulse received by the nerve is about 25 Hz. The preferred fixed
voltage received by the nerve is between about 1-20 V and will typically
vary depending on the size and type of electrode and the distance between
the electrode and the nerve. In certain embodiments where the nerve is
directly attached to the nerve (or implanted adjacent to the nerve), the
fixed voltage is preferably about 1 to 4 volts, more preferably about 2
volts. In other embodiments, wherein the electrode is, for example,
injected into the patient and implanted outside of the sheath, the
voltage is preferably between about 7-15 volts and more preferably about
10 V. In embodiments wherein the current is fixed or held constant, the
preferred fixed current is about 0.5 mA to about 20 mA. Similar to
voltage, the fixed current will vary depending on the size and type of
electrode and its distance from the nerve. In those embodiments where the
electrode is adjacent to, or on, the nerve, the current is preferably
about 0.5 to 5 mA and more preferably about 3.5 mA. In those embodiments,
where the electrode is spaced from the nerve (just as an injectable
electrode outside of the sheath), the current is preferably about 7-15 mA
and more preferably about 10 mA. The pulse duration is preferably between
about 50 to 1000 uS.
[0100] Benefits of the disclosed system include the following features.
The implanted signal generator can be much smaller than a traditional
implanted generator. The surgery to implant this system can be done under
local anesthesia on an outpatient basis in a non-hospital setting
resulting in faster recovery and less scarring. Furthermore, since there
is no implanted battery, the patient does not need additional surgeries
to replace batteries, which is especially important if the patient has a
treatment protocol that requires treatments involving significant power
and duration. Also, the limited circuitry implanted in the body will be
more reliable than traditional implanted generators. Because the
treatment is powered and controlled from outside the body, changes to the
treatment protocol can be made quickly and easily. In the event of an
emergency, the patient or caregiver can quickly turn-off or remove the
power/control unit to stop treatment.
[0101] The stimulator circuit is novel in that it removes one (or more)
elements from conventional stimulators, without sacrificing performance.
In particular, the present invention removes from conventional designs
the ability of the stimulator to vary the amplitude of the stimulation
pulses. Unexpectedly, one can get substantially the same stimulatory
effect as that provided by conventional stimulators, by keeping waveform
parameters fixed, particularly the amplitude of pulses, but by then
controlling the number and timing of pulses that the nerve experiences,
in order to achieve the same physiologically desirable level of nerve
stimulation. In essence, this invention is using an adjustable number of
fixed voltage (or current) pulses with fixed duration to elicit desired
changes in nerve response.
[0102] The electrode and signal generator are primarily, but not
exclusively, intended for stimulation of the vagus nerve in the neck, for
conditions that include headache, epilepsy, asthma, anxiety/depression,
gastric motility disorders, fibromyalgia, Alzheimer's disease, stroke,
posttraumatic stress disorder, and traumatic brain injury. In those
applications, the typical signal would be square or sine pulses of fixed
amplitude approximately 2 Volts, where each pulse has a fixed duration of
200 uS. Typically 5 of these pulses would be produced every 40 mS to
produce an effective 25 Hz signal. The selection of these waveform
parameters is discussed more fully below.
[0103] Although the preferred embodiments of the invention are as
described above, it is understood that one may also modify the
capabilities of the device as follows. Optionally, the pulse command
could have an address or other identifier associated with it so that only
a particular signal generator would be activated. This would allow a
patient to have multiple implanted signal generators in the body with
each responding to its own command from the same or multiple
power/control units. Another option would be to have circuitry or a
processor in the implanted signal generator that could communicate a
signal back to the power/control unit. This signal could contain status
information such as voltage, current, number of pulses applied or other
applicable data. The antennae and RF signals in this system could also be
replaced by closely coupled coils of wire and lower frequency signals
that are inductively coupled through the body.
[0104] Another embodiment of the present invention is shown in FIG. 2,
which is a schematic diagram of an electrode-based nerve
stimulating/modulating device 302 for delivering impulses of energy to
nerves for the treatment of medical conditions. As shown, device 302 may
include an impulse generator 310; a power source 320 coupled to the
impulse generator 310; a control unit 330 in communication with the
impulse generator 310 and coupled to the power source 320; and electrodes
340 coupled via wires 345 to the impulse generator 310. In a preferred
embodiment, the same impulse generator 310, power source 320, and control
unit 330 may be used for either a magnetic stimulator or the
electrode-based stimulator 302, allowing the user to change parameter
settings depending on whether magnetic coils or the electrodes 340 are
attached, either of which may be used for the therapeutic stimulation
applications that are describe herein [application Ser. No. 13/183,765
and Publication US2011/0276112, entitled Devices and methods for
non-invasive capacitive electrical stimulation and their use for vagus
nerve stimulation on the neck of a patient, to SIMON et al.; application
Ser. No. 12/964,050 and Publication US2011/0125203, entitled Magnetic
Stimulation Devices and Methods of Therapy, to SIMON et al, which are
hereby incorporated by reference].
[0105] Although a pair of electrodes 340 is shown in FIG. 2, in practice
the electrodes may also comprise three or more distinct electrode
elements, each of which is connected in series or in parallel to the
impulse generator 310. Thus, the electrodes 340 that are shown in FIG. 2
represent all electrodes of the device collectively.
[0106] The item labeled in FIG. 2 as 350 is a volume, contiguous with an
electrode 340, that is filled with electrically conducting medium. The
conducting medium in which the electrode 340 is embedded need not
completely surround an electrode. The volume 350 is electrically
connected to the patient at a target skin surface in order to shape the
current density passed through an electrode 340 that is needed to
accomplish stimulation of the patient's nerve or tissue such as the skin.
The electrical connection to the patient's skin surface is through an
interface 351. In one embodiment, the interface is made of an
electrically insulating (dielectric) material, such as a thin sheet of
Mylar. In that case, electrical coupling of the stimulator to the patient
is capacitive. In other embodiments, the interface comprises electrically
conducting material, such as the electrically conducting medium 350
itself, or an electrically conducting or permeable membrane. In that
case, electrical coupling of the stimulator to the patient is ohmic. As
shown, the interface may be deformable such that it is form-fitting when
applied to the surface of the body. Thus, the sinuousness or curvature
shown at the outer surface of the interface 351 corresponds also to
sinuousness or curvature on the surface of the body, against which the
interface 351 is applied, so as to make the interface and body surface
contiguous.
[0107] The control unit 330 controls the impulse generator 310 to generate
a signal for each of the device's electrodes (or magnetic coils). The
signals are selected to be suitable for amelioration of a particular
medical condition, when the signals are applied non-invasively to a
target nerve or tissue via the electrodes 340. It is noted that nerve
stimulating/modulating device 302 may be referred to by its function as a
pulse generator. Patent application publications US2005/0075701 and
US2005/0075702, both to SHAFER, contain descriptions of pulse generators
that may be applicable to the present invention. By way of example, a
pulse generator is also commercially available, such as Agilent 33522A
Function/Arbitrary Waveform Generator, Agilent Technologies, Inc., 5301
Stevens Creek Blvd Santa Clara Calif. 95051.
[0108] The control unit 330 may also comprise a general purpose computer,
comprising one or more CPU, computer memories for the storage of
executable computer programs (including the system's operating system)
and the storage and retrieval of data, disk storage devices,
communication devices (such as serial and USB ports) for accepting
external signals from the system's keyboard, computer mouse, and
touchscreen, as well as any externally supplied physiological signals
(see FIG. 1C), analog-to-digital converters for digitizing externally
supplied analog signals such as physiological signals (see FIG. 1C),
communication devices for the transmission and receipt of data to and
from external devices such as printers and modems that comprise part of
the system, hardware for generating the display of information on
monitors that comprise part of the system, and busses to interconnect the
above-mentioned components. Thus, the user may operate the system by
typing instructions for the control unit 330 at a device such as a
keyboard and view the results on a device such as the system's computer
monitor, or direct the results to a printer, modem, and/or storage disk.
Control of the system may be based upon feedback, including biofeedback,
measured from externally supplied physiological or environmental signals
(see FIG. 1C). Alternatively, the control unit 330 may have a compact and
simple structure, for example, wherein the user may operate the system
using only an on/off switch and power control wheel or knob. In a section
below, a preferred embodiment is described wherein the stimulator housing
has a simple structure, but other components of the control unit 330 are
distributed into other discrete devices (see FIG. 6).
[0109] Parameters for the nerve or tissue stimulation include power level,
frequency and train duration (or pulse number). The stimulation
characteristics of each pulse, such as depth of penetration, strength and
selectivity, depend on the rise time and peak electrical energy
transferred to the electrodes, as well as the spatial distribution of the
electric field that is produced by the electrodes. The rise time and peak
energy are governed by the electrical characteristics of the stimulator
and electrodes, as well as by the anatomy of the region of current flow
within the patient. In one embodiment of the invention, pulse parameters
are set in such as way as to account for the detailed anatomy surrounding
the nerve that is being stimulated [Bartosz SAWICKI, Robert Szmurto,
Przemystaw Ptonecki, Jacek Starzynski, Stanislaw Wincenciak, Andrzej
Rysz. Mathematical Modelling of Vagus Nerve Stimulation. pp. 92-97 in:
Krawczyk, A. Electromagnetic Field, Health and Environment: Proceedings
of EHE'07. Amsterdam, 105 Press, 2008]. Pulses may be monophasic,
biphasic or polyphasic. Embodiments of the invention include those that
are fixed frequency, where each pulse in a train has the same
inter-stimulus interval, and those that have modulated frequency, where
the intervals between each pulse in a train can be varied. The preferred
pulse parameters are described in a later section of this application.
[0110] Preferred Embodiments of the Electrode-Based Stimulator
[0111] The electrodes (or magnetic coils) of the invention are applied to
the surface of the neck, or to some other surface of the body, and are
used to deliver electrical energy non-invasively to a nerve. The vagus
nerve has previously been stimulated non-invasively, using electrodes
applied via leads to the surface of the skin. It has also been stimulated
non-electrically through the use of mechanical vibration [HUSTON J M,
Gallowitsch-Puerta M, Ochani M, Ochani K, Yuan R, Rosas-Ballina Met al
(2007). Transcutaneous vagus nerve stimulation reduces serum high
mobility group box 1 levels and improves survival in murine sepsis. Crit
Care Med 35: 2762-2768; GEORGE M S, Aston-Jones G. Noninvasive techniques
for probing neurocircuitry and treating illness: vagus nerve stimulation
(VNS), transcranial magnetic stimulation (TMS) and transcranial direct
current stimulation (tDCS). Neuropsychopharmacology 35(1, 2010):301-316].
However, no such reported uses of noninvasive vagus nerve stimulation
were directed to biofeedback applications. U.S. Pat. No. 7,340,299,
entitled Methods of indirectly stimulating the vagus nerve to achieve
controlled asystole, to John D. PUSKAS, discloses the stimulation of the
vagus nerve using electrodes placed on the neck of the patient, but that
patent is unrelated to biofeedback. Non-invasive electrical stimulation
of the vagus nerve has also been described in Japanese patent application
JP2009233024A with a filing date of Mar. 26, 2008, entitled Vagus Nerve
Stimulation System, to Fukui YOSHIHOTO, in which a body surface electrode
is applied to the neck to stimulate the vagus nerve electrically.
However, that application is also unrelated to biofeedback. In patent
publication US20080208266, entitled System and method for treating nausea
and vomiting by vagus nerve stimulation, to LESSER et al., electrodes are
used to stimulate the vagus nerve in the neck to reduce nausea and
vomiting, but this too is unrelated to biofeedback.
[0112] Patent application US2010/0057154, entitled Device and method for
the transdermal stimulation of a nerve of the human body, to DIETRICH et
al., discloses a non-invasive transcutaneous/transdermal method for
stimulating the vagus nerve, at an anatomical location where the vagus
nerve has paths in the skin of the external auditory canal. Their
non-invasive method involves performing electrical stimulation at that
location, using surface stimulators that are similar to those used for
peripheral nerve and muscle stimulation for treatment of pain
(transdermal electrical nerve stimulation), muscle training (electrical
muscle stimulation) and electroacupuncture of defined meridian points.
The method used in that application is similar to the ones used in patent
U.S. Pat. No. 4,319,584, entitled Electrical pulse acupressure system, to
McCALL, for electroacupuncture; patent U.S. Pat. No. 5,514,175 entitled
Auricular electrical stimulator, to KIM et al., for the treatment of
pain; and patent U.S. Pat. No. 4,966,164, entitled Combined sound
generating device and electrical acupuncture device and method for using
the same, to COLSEN et al., for combined continuous and monotonous
sound/electroacupuncture. A related application is US2006/0122675,
entitled Stimulator for auricular branch of vagus nerve, to LIBBUS et al.
Similarly, U.S. Pat. No. 7,386,347, entitled Electric stimulator for
alpha-wave derivation, to CHUNG et al., described electrical stimulation
of the vagus nerve at the ear. Patent application US2008/0288016,
entitled Systems and Methods for Stimulating Neural Targets, to AMURTHUR
et al., also discloses electrical stimulation of the vagus nerve at the
ear. U.S. Pat. No. 4,865,048, entitled Method and apparatus for drug free
neurostimulation, to ECKERSON, teaches electrical stimulation of a branch
of the vagus nerve behind the ear on the mastoid processes, in order to
treat symptoms of drug withdrawal. KRAUS et al described similar methods
of stimulation at the ear [KRAUS T, Hosl K, Kiess O, Schanze A, Kornhuber
J, Forster C (2007). BOLD fMRI deactivation of limbic and temporal brain
structures and mood enhancing effect by transcutaneous vagus nerve
stimulation. J Neural Transm 114: 1485-1493]. However, none of the
disclosures in these patents or patent applications for electrical
stimulation of the vagus nerve near the ear are used to in connection
with biofeedback.
[0113] Embodiments of the present invention may differ with regard to the
number of electrodes that are used, the distance between electrodes, and
whether disk or ring electrodes are used. In preferred embodiments of the
method, one selects the electrode configuration for individual patients,
in such a way as to optimally focus electric fields and currents onto the
selected nerve, without generating excessive currents on the surface of
the skin. This tradeoff between focality and surface currents is
described by DATTA et al. [Abhishek DATTA, Maged Elwassif, Fortunato
Battaglia and Marom Bikson. Transcranial current stimulation focality
using disc and ring electrode configurations: FEM analysis. J. Neural
Eng. 5 (2008): 163-174]. Although DATTA et al. are addressing the
selection of electrode configuration specifically for transcranial
current stimulation, the principles that they describe are applicable to
peripheral nerves as well [RATTAY F. Analysis of models for extracellular
fiber stimulation. IEEE Trans. Biomed. Eng. 36 (1989): 676-682].
[0114] A preferred embodiment of an electrode-based stimulator is shown in
FIG. 3. As shown, the stimulator (30) comprises two heads (31) and a
connecting part that joins them. Each head (31) contains a stimulating
electrode. The connecting part of the stimulator contains the electronic
components and a battery (not shown) that are used to generate the
signals that drive the electrodes. However, in other embodiments of the
invention, the electronic components that generate the signals that are
applied to the electrodes may be separate, but connected to the electrode
head (31) using wires or wireless communication with the heads.
Furthermore, other embodiments of the invention may contain a single such
head or more than two heads.
[0115] Heads of the stimulator (31) are applied to a surface of the
patient's body, during which time the stimulator may be held in place by
straps or frames or collars, or the stimulator may be held against the
patient's body by hand. In either case, the level of stimulation power
may be adjusted with a wheel (34) that also serves as an on/off switch. A
light (35) is illuminated when power is being supplied to the stimulator.
An optional cap may be provided to cover each of the stimulator heads
(31), to protect the device when not in use, to avoid accidental
stimulation, and to prevent material within the head from leaking or
drying. Thus, in this embodiment of the invention, mechanical and
electronic components of the stimulator (impulse generator, control unit,
and power source) are compact, portable, and simple to operate.
[0116] Details of preferred embodiments of the stimulator heads are
described in co-pending, commonly assigned applications that were cited
in the section Cross Reference to Related Applications. As described in
those applications, the stimulator designs situate the electrodes of the
stimulator (340 in FIG. 2) remotely from the surface of the skin, within
a chamber that is filled with conducting material (350 in FIG. 2). Thus,
the conducting material is placed in a chamber between the electrode and
the exterior component of the stimulator head that contacts the skin (351
in FIG. 2), thereby allowing for current to pass from the electrode to
the skin. An embodiment of a stimulator head 31 is shown in FIG. 4. FIG.
4A shows a section through one of the two stimulator heads 31 that are
shown in FIG. 3. The outer structure of the stimulator head 31 supports
the chamber 32 that is filled with conducting material 350. The electrode
340 is shown in FIG. 4A to be a conducting metal screw, to which a wire
(345 in FIG. 2) from the stimulator's impulse generator (310 in FIG. 2)
is attached. The interface 351 of the stimulator head, which contacts the
surface of the skin, is shown in FIG. 4A to comprise a disc that is made
of a conducting metal, such as stainless steel. Assembly of the interface
351, chamber 32, and electrode 340 is illustrated in FIG. 4B with an
exploded view. The conducting material 350 may be added to the chamber 32
before the electrode 340 is screwed into the chamber 32.
[0117] One of the novelties of such a design is that the stimulator, along
with a correspondingly suitable stimulation waveform (see below), shapes
the electric field, producing a selective physiological response by
stimulating that nerve, but avoiding substantial stimulation of nerves
and tissue other than the target nerve, particularly avoiding the
stimulation of nerves that produce pain. The design may, however,
stimulate tactile nerves of the skin by superimposing stimulation
waveforms that are directed individually to the deep nerve and to the
skin nerves. The shaping of the electric field is described in terms of
the corresponding electromagnetic field equations in co-pending, commonly
assigned application US20110230938 (application Ser. No. 13/075,746),
entitled Devices and methods for non-invasive electrical stimulation and
their use for vagal nerve stimulation on the neck of a patient, to SIMON
et al., which is hereby incorporated by reference.
[0118] Significant portions of the control unit (330 in FIG. 2) of the
vagus nerve stimulator may reside in controller components that are
physically separate from the housing of the stimulator (30 in FIG. 3). In
such embodiments, separate components of the controller and stimulator
housing may generally communicate with one another wirelessly. Thus, the
use of wireless technology avoids the inconvenience, size constraints,
and distance limitations of interconnecting cables. A more complete
rationale for physically separating components of the control unit is
provided in a commonly assigned, co-pending application entitled MEDICAL
SELF-TREATMENT USING NON-INVASIVE VAGUS NERVE STIMULATION, to SIMON et
al., which is hereby incorporated by reference.
[0119] Accordingly, an embodiment of the invention includes a docking
station (40 in FIG. 3C) that may also be used as a recharging power
supply for the stimulator housing (30 in FIG. 3). The docking station may
send/receive data to/from the stimulator housing, and may send/receive
data to/from databases and other components of the system, including
those that are accessible via the internet. Thus, prior to any particular
stimulation session, the docking station may load into the stimulator
parameters of the session, including stimulation waveform parameters.
[0120] In a preferred embodiment, the docking station also limits the
amount of stimulation energy that may be consumed by the patient in the
stimulation session, by charging the stimulator's rechargable battery
with only a specified amount of releasable electrical energy. Note that
this is generally different than setting a parameter to restrict the
duration of a stimulation session. As a practical matter, the stimulator
may therefore use two batteries, one for stimulating the patient (the
charge of which may be limited by the docking station) and the other for
performing other functions such as data transmission. Methods for
evaluating a battery's charge or releasable energy are known in the art,
for example, in patent U.S. Pat. No. 7,751,891, entitled Power supply
monitoring for an implantable device, to ARMSTRONG et al. Alternatively,
control components within the stimulator housing may monitor the amount
of stimulation energy that has been consumed during a stimulation session
and stop the stimulation session when a limit has been reached,
irrespective of the time when the limit has been reached.
[0121] Refer now to the docking station that is shown as item 40 in FIG.
3C. The stimulator housing 30 and docking station 40 can be connected to
one another by inserting the connector 36 near the center of the base 38
of the stimulator housing 30 into a mated connector 42 of the docking
station 40. As shown in FIG. 3, the docking station 30 has an indentation
or aperture 41 that allows the base 38 of the stimulator housing 30 to be
seated securely into the docking station. The connector 36 of the
stimulator housing is recessed in an aperture 37 of the base of the
stimulator housing 30 that may be covered by a detachable or hinged cover
when the stimulator housing is not attached to the docking station (not
shown).
[0122] The mated connectors 36 and 42 have a set of contacts that have
specific functions for the transfer of power to charge a rechargable
battery in the stimulator housing 30 and to transfer data bidirectionally
between the stimulator housing and docking station. As a safety feature,
the contacts at the two ends of the mated connector are connected to one
another within the stimulator housing and within the docking station,
such that if physical connection is not made at those end contacts, all
the other contacts are disabled via active switches. Also, the connectors
36 and 42 are offset from the center of the base 38 of the stimulator
housing 30 and from the center of the indentation or aperture 41 of the
docking station 40, so that the stimulator housing can be inserted in
only one way into the docking station. That is to say, when the
stimulator housing 30 is attached to the docking station 40, the front of
the stimulator housing 30 must be on the front side of the docking
station 40. As shown, the back side of the docking station has an on/off
switch 44 and a power cord 43 that attaches to a wall outlet. The docking
station 40 also has ports (e.g., USB ports) for connecting to other
devices, one of which 45 is shown on the side of the station, and others
of which are located on the front of the station (not shown). The front
of the docking station has colored lights to indicate whether the docking
station has not (red) or has (green) charged the stimulator so as to be
ready for a stimulation session.
[0123] Through cables to the communication port 45, the docking station 40
can communicate with the different types of devices, such as those
illustrated in FIG. 5. Handheld devices may resemble conventional remote
controls with a display screen (FIG. 5A) or mobile phones (FIG. 5B).
Other type of devices with which the docking station may communicate are
touchscreen devices (FIG. 5C) and laptop computers (FIG. 5D). As
described below, such communication may also be performed wirelessly.
[0124] The communication connections between different components of the
stimulator's controller are shown in FIG. 6, which is an expanded
representation of the control unit 330 in FIG. 2. Connection between the
docking station controller components 332 and components within the
stimulator housing 331 is denoted in FIG. 6 as 334. For example, that
connection is made when the stimulator housing is connected to the
docking station as described above. Connection between the docking
station controller components 332 and devices 333 such as those shown in
FIG. 5 (generally internet-based components) is denoted as 335.
Connection between the components within the stimulator housing 331 and
devices 333 such as those shown in FIG. 5 (generally internet-based
components) is denoted as 336. Different embodiments of the invention may
lack one or more of the connections. For example, if the connection
between the stimulator housing and the devices 333 is only through the
docking station controller components, then in that embodiment of the
invention, only connections 334 and 335 would be present.
[0125] The connections 334, 335 and 336 in FIG. 6 may be wired or
wireless. For example, if the controller component 333 is the mobile
phone shown in FIG. 5B, the connection 335 to a docking stationport (45
in FIG. 3) could be made with a cable to the phone's own docking port.
Similarly, if the controller component 333 is the laptop computer shown
in FIG. 5D, the connection 335 to a docking stationport (45 in FIG. 3)
could be made with a cable to a USB port on the computer. However, the
preferred connections 334, 335, and 336 will be wireless.
[0126] Although infrared or ultrasound wireless control might be used to
communicate between components of the controller, they are not preferred
because of line-of-sight limitations. Instead, in the present disclosure,
the communication between devices preferably makes use of radio
communication within unlicensed ISM frequency bands (260-470 MHz, 902-928
MHz, 2400-2.4835 GHz). Components of a radio frequency system in devices
331, 332, and 333 typically comprise a system-on-chip transceiver with an
integrated microcontroller; a crystal; associated balun & matching
circuitry, and an antenna [Dag GRINI. RF Basics, RF for Non-RF Engineers.
Texas Instruments, Post Office Box 655303, Dallas, Tex. 75265, 2006].
[0127] Transceivers based on 2.4 GHz offer high data rates (greater than 1
Mbps) and a smaller antenna than those operating at lower frequencies,
which makes them suitable for with short-range devices. Furthermore, a
2.4 GHz wireless standard (Bluetooth, Wi-Fi, and ZigBee) may be used as
the protocol for transmission between devices. Although the ZigBee
wireless standard operates at 2.4 GHz in most jurisdictions worldwide, it
also operates in the ISM frequencies 868 MHz in Europe, and 915 MHz in
the USA and Australia. Data transmission rates vary from 20 to 250
kilobits/second with that standard.
[0128] FIG. 6 also shows that sensor devices that measure physiological
and environmental signals may connect to the control unit 330 via any of
its subsystems (stimulator body 331, docking station 332, and handheld or
internet-based devices 333). Because many commercially available
health-related sensors may operate using ZigBee, its use may be
recommended for applications in which the controller adjusts the
patient's vagus nerve stimulation based on the physiological sensors'
values, as described in connection with FIG. 1 [ZigBee Wireless Sensor
Applications for Health, Wellness and Fitness. ZigBee Alliance 2400
Camino Ramon Suite 375 San Ramon, Calif. 94583]. Systems for connecting
smartphones to physiological sensors using Bluetooth may also be used.
For example, BioZen, which is designed specifically for biofeedback
applications, is based on the open source framework Bluetooth Sensor
Processing for Android smartphones and is freely available. It may
connect wirelessly to many commercially available physiological sensor
devices [Anonymous. BIOZEN User's Manual. United States Defense
Department National Center for Telehealth and Technology. 9933 West Hayes
Street, Joint Base Lewis-McChord, Wash. 98431, pp. 1-16, 2013].
Commercially available wired and wireless physiological sensor
measurement devices using the e-Health Sensor Platform for Arduino and
Raspberry Pi are also suitable for incorporation into, or connection
with, the stimulator housing 30 or the docking station 40 in FIG. 3
[Anonymous. e-Health Sensor Platform for Arduino and Raspberry Pi
(Biometric/Medical Applications). Technical literature from Cooking Hacks
(the open hardware division of Libelium). Libelium Comunicaciones
Distribuidas S.L., C/Maria de Luna 11, nave 17, C.P. 50018, Zaragoza,
Spain. pp. 1-159, 2013]. Other such methods for incorporating
physiological sensors into biofeedback systems have also been described
[Guan-Zheng LIU, Bang-Yu Huang and Lei Wang. A Wearable Respiratory
Biofeedback System Based on Generalized Body Sensor Network. TELEMEDICINE
and e-HEALTH 17(5, 2011):348-357]. Use of such sensors is described more
completely below in a section on the use of biofeedback and automatic
control theory methods to improve treatment of individual patients.
[0129] Application of the Stimulator to the Neck of the Patient
[0130] In different methodological embodiments of the present invention,
selected nerve fibers are stimulated by the disclosed electrical
stimulation devices. These methods include noninvasive stimulation at a
particular location on the patient's neck. Nerves stimulated at that
location comprise the vagus nerve, and in some embodiments, cutaneous
nerve endings. At that location in the neck, the vagus nerve is situated
within the carotid sheath. The left vagus nerve is sometimes selected for
stimulation, because stimulation of the right vagus nerve may produce
undesired effects on the heart. However, depending on the application,
the right vagus nerve or both right and left vagus nerves may be
stimulated instead.
[0131] To find the appropriate location to stimulate on the neck, the
location of the carotid sheath will first be ascertained by any method
known in the art, e.g., by feel and anatomical inference, or preferably
by ultrasound imaging [KNAPPERTZ V A, Tegeler C H, Hardin S J, McKinney W
M. Vagus nerve imaging with ultrasound: anatomic and in vivo validation.
Otolaryngol Head Neck Surg 118(1, 1998):82-85; GIOVAGNORIO F and
Martinoli C. Sonography of the cervical vagus nerve: normal appearance
and abnormal findings. AJR Am J Roentgenol 176(3, 2001):745-749]. The
stimulator is then positioned at the level of about the fifth to sixth
cervical vertebra.
[0132] FIG. 7 illustrates application of the device 30 shown in FIG. 3 to
the patient's neck, in order to stimulate the cervical vagus nerve on
that side of the neck. For reference, FIG. 7 shows the locations of the
following vertebrae: first cervical vertebra 71, the fifth cervical
vertebra 75, the sixth cervical vertebra 76, and the seventh cervical
vertebra 77.
[0133] FIG. 8 shows the stimulator 30 applied to the neck of a child,
which is partially immobilized with a foam cervical collar 78 that is
similar to ones used for neck injuries and neck pain. The collar is
tightened with a strap 79, and the stimulator is inserted through a hole
in the collar to reach the child's neck surface. As shown, the stimulator
is turned on and off with a control knob, and the amplitude of
stimulation may also be adjusted with the control knob that is located on
the stimulator. In other models, the control knob is absent or disabled,
and the stimulator may be turned on and off remotely, using a wireless
controller (see FIG. 5A) that may be used to adjust the stimulation
parameters of the controller (e.g., on/off, stimulation amplitude,
stimulation waveform frequency, etc.).
[0134] FIGS. 9 and 10 illustrate some of the major structures of the neck,
in order to point out structures that could potentially be stimulated
electrically, when the stimulator is positioned as in FIGS. 7 and 8. For
comparison with FIG. 7, FIG. 9A illustrates the approximate locations of
the cervical vertebrae C1 through C7. The thyroid cartilage, the largest
of the cartilages that make up the cartilage structure in and around the
trachea that contains the larynx, lies at the vertebral levels of C4 and
C5. The laryngeal prominence 111 (Adam's apple) in the middle of the neck
is formed by the thyroid cartilage at approximately vertebral level C4.
[0135] As shown in FIG. 9A, the common carotid artery 100 extends from the
base of the skull 102 through the neck 104 to the first rib and sternum
(not shown). Carotid artery 100 includes an external carotid artery 106
and an internal carotid artery 108 and is protected by fibrous connective
tissue, namely, the carotid sheath. The three major structures within the
carotid sheath are the common carotid artery 100, the internal jugular
vein 110 and the vagus nerve (not shown).
[0136] Proceeding from the skin and fat of the neck to the carotid sheath,
the shortest line from the stimulator 30 to the vagus nerve may pass
successively through the platysma muscle 82, the sternocleidomastoid
muscle 65, and the carotid sheath (see FIG. 9B and 9C). The anatomy along
this line is shown in more detail in FIG. 10, which is a cross-section of
half of the neck at vertebra level C6. The vagus nerve 60 is identified
in FIG. 10, along with the carotid sheath 61 that is identified there in
bold peripheral outline. The carotid sheath encloses not only the vagus
nerve, but also the internal jugular vein 62 and the common carotid
artery 63. Structures that may be identified near the surface of the neck
include the external jugular vein 64 and the sternocleidomastoid muscle
65, which protrudes when the patient turns his or her head. Additional
organs in the vicinity of the vagus nerve include the trachea 66, thyroid
gland 67, esophagus 68, scalenus anterior muscle 69, scalenus medius
muscle 70, levator scapulae muscle 71, splenius colli muscle 72,
semispinalis capitis muscle 73, semispinalis colli muscle 74, longus
colli muscle and longus capitis muscle 75. The sixth cervical vertebra 76
is shown with bony structure indicated by hatching marks. Additional
structures shown in the figure are the phrenic nerve 77, sympathetic
ganglion 78, brachial plexus 79, vertebral artery and vein 80,
prevertebral fascia 81, platysma muscle 82, omohyoid muscle 83, anterior
jugular vein 84, sternohyoid muscle 85, sternothyroid muscle 86, and skin
with associated fat 87.
[0137] The skin 87 at this location has innervation that is associated
with particular dermatomes, although the dermatome extent varies from
individual to individual [LADAK A, Tubbs R S, Spinner R J. Mapping
sensory nerve communications between peripheral nerve territories. Clin
Anat. 2013 Jul. 3. doi: 10.1002/ca.22285, pp. 1-10; C. E. POLETTI. C2 and
C3 pain dermatomes in man. Cephalalgia 11(3, 1991):155-159]. Men and
women also have a different skin anatomy there because the skin of men
may contain a significantly greater number of hair follicles.
[0138] It is also understood that there may be significant individual
variation in internal neck anatomy, and this should be taken into account
when positioning the stimulator 30 [commonly assigned and co-pending
patent application entitled IMPLANTATION OF WIRELESS VAGUS NERVE
STIMULATORS, to SIMON et al., which is hereby incorporated by reference].
In addition, for patients having necks that are unusually wrinkled or
that contain large amounts of fatty tissue, the skin may have to be first
taped or otherwise made to conform to a flattened or smooth configuration
in order for the methods of the invention to be applied successfully.
[0139] Once the stimulator has been preliminarily positioned, testing may
be performed in order to ascertain that the position is correct. After
testing, the correct position may be marked on the patient's skin, for
example with fluorescent dyes that are excited with infrared or
ultraviolet light, to facilitate subsequent placement of the stimulator
[commonly assigned and co-pending patent application U.S. Ser. No.
13/872,116, entitled DEVICES AND METHODS FOR MONITORING NON-INVASIVE
VAGUS NERVE STIMULATION, to SIMON et al., which is hereby incorporated by
reference].
[0140] Use of Biofeedback and Automatic Control Theory Methods to Treat
and Train Patients
[0141] As discussed above in connection with FIG. 1C, devices and methods
according to the present invention involve combined biofeedback and
automatic control mechanisms, which begin with measurement of
physiological properties of the individual using sensors. The present
invention contemplates the measurement and processing of many types of
physiological signals, including all of those that have been used in
conventional biofeedback experiments. The following summary of the types
of signals that have been used for biofeedback is accompanied by a
description of their intended uses, which are also intended uses of the
present invention.
[0142] The physiological signals that are used currently by biofeedback
practitioners descend from experiments performed in the 1960s by
Basmajian, by Kamiya, and by Sterman. BASMAJIAN's initial contribution to
biofeedback research was to demonstrate that with the aid of auditory or
visual biofeedback signals, some normal individuals can learn to
voluntarily control the contraction of individual striated-muscle units,
and at the same time inhibit the activity of nearby muscle units. In
these experiments, the activity of the muscle unit was measured
electromyographically, which was converted to an audio or visual signal,
to which the subject could respond by attempting to contract that muscle
unit [BASMAJIAN J V. Control and training of individual motor units.
Science 141(3579, 1963):440-441].
[0143] Subsequent clinical applications of this electromyographic (EMG)
biofeedback research split into two streams. One was training individuals
to relax, including the relaxation of face and neck muscles that are
tightened as a symptom of stress, e.g., in patients with tension
headaches, chronic back pain, and anxiety. The other stream was the
medical rehabilitation of various types of motor neuron disturbance,
especially paresis and spasticity found in patients who suffer from
stroke, cerebral palsy, and dyskinesias [BASMAJIAN J V. Biofeedback in
medical practice. Can Med Assoc J 119(1, 1978): 8-10; John V. BASMAJIAN.
Research foundations of EMG biofeedback in rehabilitation. Biofeedback
and Self-Regulation 13(4, 1988):275-298; C. R. CRAM. Biofeedback
Applications. Chapter 17 In: Roberto MERLETTI and Philip A. Parker, eds.
Electromyography. Physiology, Engineering, and Noninvasive Applications.
Hoboken, N.J.: IEEE-John Wiley & Sons, 2004. pp. 435-451]. The
rehabilitation stream has been noncontroversial and fertile since its
beginnings. On the other hand, the relaxation stream has long been
controversial and competes with, or complements, progressive relaxation
therapy methods (e.g., Jacobson or Wolpe versions) and movement-based
methods (exercise, Tai Chi, etc.), as well as non-muscular forms of
stress management, including other forms of biofeedback such as
alpha/theta neurofeedback, deep breathing methods, meditation, guided
imagery, hypnosis and autogenic training [A. Barney ALEXANDER. An
experimental test of assumptions relating to the use of electromyographic
biofeedback as a general relaxation training technique. Psychophysiology
12(6, 1975):656-662; Monique MOORE, David Brown, Nisha Money, Mark Bates.
Mind-body skills for regulating the autonomic nervous system. (June 2011)
Defense Centers of Excellence for Psychological Health and Traumatic
Brain Injury. 2345 Crystal Drive, Crystal Park 4, Suite 120, Arlington
Va. 22202]
[0144] It is noteworthy that BASMAJIAN found considerable variation among
individuals in their ability to actually perform EMG biofeedback. Only
about 25% of the individuals were able to readily control contractions of
isolated muscles. About half of the individuals displayed some skill
after several hours of training, but others failed to learn to perform
any skeletal-muscle biofeedback. BASMAJIAN found no individual
characteristics that could account for the variation in muscular feedback
performance, such as age, sex, manual dexterity, education, degree of
extroversion, or nervous vs. calm personality.
[0145] Kamiya and Sterman initiated another form of biofeedback, in which
the physiological signal that is used for training is derived from the
subject's electroencephalogram (EEG). This type of biofeedback is also
known as neurofeedback, to distinguish it from peripheral biofeedback,
which is the use of a signal derived from a site other than the
brain/spinal cord. KAMIYA reported that when subjects are presented with
an audio tone whenever their EEG contains significant alpha waves
(signals in the range of 8 to 12 Hz), some individuals can learn to
voluntarily suppress and/or enhance the time spent in that alpha state,
especially individuals who practice some form of meditation [Joe KAMIYA.
Operant control of the EEG alpha rhythm and some of its reported effects
on consciousness. Chapter 35, pp. 507-517. In: Charles T. Tart, ed.
Altered states of consciousness; a book of readings. New York: Wiley,
1969]. Alpha (and alpha/theta) neurofeedback is said to allow an
individual to remain in a state of deep relaxation without falling
asleep. However, the ability of individuals to learn to control their
alpha waves was soon disputed, leading to methodological arguments about
how the alpha wave activity was to be measured and presented to the
subject, which resulted in a subsequent loss of interest in alpha wave
training [LYNCH, J. L., Paskewitz, D. and Orne, M. T. Some factors in the
feedback control of the human alpha rhythm. Psychosomatic Medicine 36(5,
1974):399-410; James V. HARDT and Joe Kamiya. Conflicting results in EEG
alpha feedback studies. Why amplitude integration should replace time.
Biofeedback and Self-Regulation 1(1, 1976):63-75].
[0146] At about the same time, STERMAN and colleagues were investigating
neurofeedback in cats and in humans, using visual and audio biofeedback
from EEG sensorimotor waves (signals in the range of 12 to 15 Hz). Over
the course of several months, some individuals were able to learn to have
some control over those waves. Anecdotally, some such epileptic
individuals were reported to have a decrease in seizure frequency [M. B.
STERMAN, L. R. Macdonald, and R. K. Stone. Biofeedback training of the
sensorimotor electroencephalogram rhythm in man: effects on epilepsy.
Epilepsia 15(1974): 395-416; Wanda WYRWICKA and Maurice B. Sterman.
Instrumental conditioning of sensorimotor cortex EEG spindles in the
waking cat. Physiology and Behavior 3(1968):703-707].
[0147] By combining different EEG frequency bands with different scalp
locations at which the EEG is measured, it is possible to devise a large
number of potential neurofeedback protocols. EEG frequency bands that may
be selected comprise the delta (1-4 Hz), theta (4-8 Hz), alpha (8-12 Hz),
beta (13-21 Hz), sensorimotor (SMR, 12-15 Hz), high beta (20-32 Hz), and
gamma (38-42 Hz). EEG electrodes may be placed on the scalp at, or
between, each of the many scalp locations defined by the International
10-20 system. The EEG voltages may be measured relative to a ground clip
on one or both of the patient's ears, mastoids, nose, or inion; or
relative to particular scalp electrodes; or relative to a weighted
combination of scalp electrodes. Single-channel EEG neurofeedback may use
a signal that is derived from a particular scalp location. Alternatively,
two- or multi-channel EEG may use signals derived from two or more scalp
locations, in which case the signal(s) used for biofeedback may involve,
for example, measurement of the coherence between signals at different
scalp locations, instead of simply the voltages at those locations. The
neurofeedback may also involve training sequentially at one, then another
scalp location. An example of two-channel EEG neurofeedback is U.S. Pat.
No. 5,280,793, entitled Method and system for treatment of depression
with biofeedback using left-right brain wave asymmetry, to ROSENFELD.
[0148] More generally, the neurofeedback signal may be constructed to be
any function of the voltages recorded from various scalp locations,
including those used to construct comprehensive topographic brain maps in
quantitative EEG (QEEG). Historically, neurofeedback emphasized
measurements at scalp locations C3 and C4; at Fz, Cz, and Pz; and at C3
and Cz. The rationale for picking those locations was that they lie along
the sensorimotor strip and the cingulate gyrus that divide the brain into
four quadrants. Those locations were typically used for biofeedback
involving beta and/or SMR waves, as well as theta and high beta waves, or
alpha and theta waves for relaxation, or at a particular frequency such
as 14 Hz. The more recent practice is to perform a comprehensive
quantitative EEG, and then pick scalp locations for neurofeedback
depending on how the individual's EEG deviates from signals found in
normative databases. Other more recent practices are (1) to measure blood
flow at different scalp or forehead regions by calculating the ratio of
reflected light at 850 nm and 660 nm, then use this signal for
biofeedback (near infrared hemoencephalography); and (2) to subject the
patient to periodically varying light and/or sound at particular
frequencies or combinations of frequencies, in an attempt to modify the
patient's EEG (brainwave entrainment), in which the selected frequencies
might also be varied depending the current EEG waveforms [John N. DEMOS.
Getting Started with Neurofeedback. New York: W.W. Norton & Co., 2005.
pp. 1-281].
[0149] Neurofeedback is not approved by the U.S. Food and Drug
Administration for the treatment of any disorder. However, because it is
a form of biofeedback, and because biofeedback devices have been approved
by the FDA for relaxation training, practitioners of neurofeedback use it
to teach patients "focused relaxation," irrespective of the medical
classification of the patient, with the understanding that other forms of
biofeedback are also used for relaxation, e.g, muscle tension relaxation
using EMG biofeedback. Medical insurance does not generally reimburse for
neurofeedback training, although it does reimburse for other forms of
biofeedback.
[0150] Nevertheless, clinical data may eventually demonstrate the efficacy
and effectiveness of some form of neurofeedback training for some of the
conditions with which it is currently used--e.g., attention deficit
hyperactivity disorder (ADHD), learning disabilities, seizures,
depression, acquired brain injuries, substance abuse, autism, and anxiety
[Carolyn YUCHA and Doil Montogmery. Evidence-Based Practice in
Biofeedback and Neurofeedback. Wheatridge, Colo.: Association for Applied
Psychophysiology and Biofeedback (AAPB), 2008. pp. 1-81; MONASTRA V J,
Lynn S, Linden M, Lubar J F, Gruzelier J, LaVaque T J.
Electroencephalographic biofeedback in the treatment of
attention-deficit/hyperactivity disorder. Appl Psychophysiol Biofeedback
30(2, 2005):95-114; Yoko NAGAI. Biofeedback and epilepsy. Curr Neurol
Neurosci Rep 11(2011):443-450; Robert COBEN, Michael Linden and Thomas E.
Myers. Neurofeedback for autistic spectrum disorder: A review of the
literature. Appl Psychophysiol Biofeedback 35(2010):83-105; Kathi J.
KEMPER. Biofeedback and mental health. Alternative and Complementary
Therapies 16(4, 2010): 208-212].
[0151] Little is known about: (1) why some individuals appear to be able
to modulate their own EEG, but most others can do so only with
difficulty, if at all; (2) the mechanism for how a competent individual
learns to voluntarily modify the EEG during the neurofeedback session,
beyond focusing on the feedback signal and the task of modulating it, as
well as avoiding muscular or mental tension that would interfere with
that task; and (3) whether such an individual is able to perceive his or
her actual brain state, given that the brain does not contain
interoceptors analogous to the sensors that are present outside of the
central nervous system. Some information in this regard comes from
noninvasive images of the individual's brain using functional magnetic
resonance imaging (fMRI), which are acquired in conjunction with a
neurofeedback session [Boris KOTCHOUBEY, Andrea Kubler, Ute Strehl, Herta
Flor, and Niels Birbaumer. Can Humans Perceive Their Brain States?
Consciousness and Cognition 11(2002):98-113; ROS T, Theberge J, Frewen P
A, Kluetsch R, Densmore M, Calhoun V D, Lanius R A. Mind over chatter:
plastic up-regulation of the fMRI salience network directly after EEG
neurofeedback. Neuroimage 65(2013):324-335].
[0152] The fMRI images have been used by themselves (i.e., without an EEG
signal) to generate a signal that the subject uses for neurofeedback,
with the objective of having the subject learn to modulate the activity
of particular visualizable structures or circuits within the brain
[HAMPSON M, Scheinost D, Qiu M, Bhawnani J, Lacadie C M, Leckman J F,
Constable R T, Papademetris X. Biofeedback of real-time functional
magnetic resonance imaging data from the supplementary motor area reduces
functional connectivity to subcortical regions. Brain Connect 1(1,
2011):91-98; R. Cameron CRADDOCK, Jonathan Lisinski, Pearl Chiu, Helen
Mayberg, Stephen LaConte. Real-time tracking and biofeedback of the
default mode network. Poster No. 648, Jun. 11, 2012. In: Proc. 18th OHBM
Meeting., Jun. 10-14, 2012. Beijing China. Organization for Human Brain
Mapping. 5841 Cedar Lake Road, Suite 204 Minneapolis, Minn. 55416, pp.
1-3; VEIT R, Singh V, Sitaram R, Caria A, Rauss K, Birbaumer N. Using
real-time fMRI to learn voluntary regulation of the anterior insula in
the presence of threat-related stimuli. Soc Cogn Affect Neurosci 7(6,
2012):623-634; SCHEINOST D, Stoica T, Saksa J, Papademetris X, Constable
R T, Pittenger C, Hampson M. Orbitofrontal cortex neurofeedback produces
lasting changes in contamination anxiety and resting-state connectivity.
Transl Psychiatry 3(2013):e250, pp 1-6; Mark CHIEW. Development and
application of methods for real-time fMRI neurofeedback. PhD
dissertation. University of Toronto (Ontario, Canada), 2013. pp 1-134;
HALLER S, Birbaumer N, Veit R. Real-time fMRI feedback training may
improve chronic tinnitus. Eur Radiol 20(3, 2010):696-703].
[0153] The ability of an individual to voluntarily modulate his or her EEG
(e.g., slow cortical potentials, event-related potentials,
sensorimotor-rhythm or mu-rhythm) has other potential uses than medical
or behavioral therapy. In particular, control over the EEG has been
investigated in connection with the desire to allow normal,
neurologically damaged, or paralyzed individuals to control a computer
interface using thought alone [KUBLER A, Kotchoubey B, Hinterberger T et
al. The thought translation device: a neurophysiological approach to
communication in total motor paralysis. Exp Brain Res 2(1999):223-232;
BIRBAUMER N, Ghanayim N, Hinterberger T et al. A spelling device for the
paralysed. Nature 6725(1999):297-298; HINTERBERGER T, Veit R, Wilhelm B,
Weiskopf N, Vatine J J, Birbaumer N. Neuronal mechanisms underlying
control of a brain-computer interface. Eur J Neurosci 21(11,
2005):3169-3181; SANTHANAM G, Ryu S I, Yu B M, Afshar A, Shenoy K V. A
high-performance brain-computer interface. Nature 442(7099,
2006):195-198; Eberhard E. FETZ. Volitional control of neural activity:
implications for brain-computer interfaces. J Physiol 579 (3,
2007):571-579; BIRBAUMER N, Cohen L G. Brain-computer interfaces:
communication and restoration of movement in paralysis. J Physiol 579(3,
2007):621-636; Mikhail A. LEBEDEV, Roy E. Grist, and Miguel A. L.
Nicolelis. Building brain--machine interfaces to restore neurological
functions. Chapter 11 (pp. 219-240) In: Nicolelis M A L, editor. Methods
for Neural Ensemble Recordings. 2nd edition. Boca Raton (Fla.): CRC
Press; 2008; BLANKERTZ, Michael Tangermann, Carmen Vidaurre, Siamac
Fazli, Claudia Sannelli, Stefan Haufe, Cecilia Maeder, Lenny Ramsey,
Irene Sturm, Gabriel Curio and Klaus-Robert Muller. The Berlin
brain-computer interface: non-medical uses of BCI technology. Front
Neurosci. 4(2010):198, pp 1-17; HADLER S, Agorastos D, Veit R, Hammer E
M, Lee S, Varkuti B, Bogdan M, Rosenstiel W, Birbaumer N, Kubler A.
Neural mechanisms of brain-computer interface control. Neuroimage 55(4,
2011):1779-1790].
[0154] Other non-medical, computer control-related applications of
biofeedback, such as the use of physiological signals to control or
interact with computer games and simulators, often use signals other than
the EEG, such as EMG, galvanic skin response, heart rate variability,
facial expressions, pupil dilation, and finger temperature [Anton NIJHOLT
and Desney Tan, eds. BrainPlay'07: Playing with Your Brain.
Brain-Computer Interfaces and Games. Proceedings of the Workshop of the
International Conference on Advances in Computer Entertainment
Technology, at Salzburg, Austria, June 2007, pp 1-53; Scott W. McQUIGGAN,
Sunyoung Lee, James C. Lester. Predicting user physiological response for
interactive environments: an inductive approach. In Proc. of the 2nd
Conf. on Artificial Intelligence and Interactive Digital Entertainment.
Palo Alto: Association for the Advancement of Artificial Intelligence,
2006, pp. 1-6; Stephen H. FAIRCLOUGH. Fundamentals of physiological
computing. Journal Interacting with Computers 21(1-2, 2009):133-145; Eric
CHAMPION and Andrew Dekker. Biofeedback And Virtual Environments.
International Journal of Architectural Computing 9(4, 2011): 377-395;
Mike AMBINDER. Biofeedback in gameplay. How Valve measures physiology to
enhance gaming experience. VALVE Software. PO Box 1688. Bellevue, Wash.
98009. 2011, pp 1-71].
[0155] The use of physiological biofeedback signals other than the EEG has
a long history, many of which had been used previously in connection with
operant or instrumental conditioning experiments. The use of
electromyographic signals (EMG) was mentioned above. Another conventional
biofeedback signal involves measurement of the electrodermal response [D.
SHAPIRO, A. B. Crider, and B. Tursky. Differentiation of an autonomic
response through operant reinforcement. Psychonom. Sci. 1(1964):147-148;
BIRK L, Crider A, Shapiro D, Tursky B. Operant electrodermal conditioning
under partial curarization. J Comp Physiol Psychol 62(1, 1966):165-166;
H. D KIMMEL. Instrumental conditioning of autonomically mediated
behavior. Psychological Bulletin 67(1967):337-345]. Yet another such
signal is hand temperature as an indicator of blood flow [J. D. SARGENT,
E. E. Green, and E.D. Walters. Preliminary report on the use of autogenic
feedback techniques in the treatment of migraine and tension headaches.
Psychosom. Med. 35(1973):129-135; FREEDMAN R R, Morris M, Norton D A,
Masselink D, Sabharwal S C, Mayes M. Physiological mechanism of digital
vasoconstriction training. Biofeedback Self Regul 13(4, 1988):299-305; R.
Sergio GUGLIELMI and Alan H. Roberts. Volitional vasomotor lability and
vasomotor control. Biological Psychology 39(1994):29-44].
[0156] Until recently, the EMG, EEG, electro-dermal response, and hand
temperature measurements have been the principal modalities used to
perform biofeedback training. Any other physiological signal could be
used, especially a signal corresponding to the particular physiological
variable that one is attempting to modify. However, such supplementary or
alternate signals may not be necessary or even useful, due to the
existence of correlations between multiple physiological variables that
are controlled by the autonomic nervous system. For example, if one is
attempting to control an individual's blood pressure, use of a blood
pressure signal for biofeedback is very much less effective than using
electro-dermal or hand temperature signals [LINDEN W, Moseley J V. The
efficacy of behavioral treatments for hypertension. Appl Psychophysiol
Biofeedback 3(1, 2006):51-63].
[0157] Over the past decade, biofeedback methods have experienced a
renaissance, due primarily to the introduction of new modalities of
biofeedback signals. One such modality was described above, namely, the
use of portions of an fMRI image of the patient's brain, instead of (or
in conjunction with), the patient's EEG. Another new modality involves
biofeedback using a signal related to heart rate variability. Heart rate
variability is conventionally assessed by examining the Fourier spectrum
of successive heart beat intervals that are extracted from an
electrocardiogram (RR-intervals). Typically, a high-frequency respiratory
component (0.15 to 0.4 Hz, centered around about 0.25 Hz, and varying
with respiration) and a slower, low frequency component (from about 0.04
to 0.13 Hz) due primarily to baroreceptor-mediated regulation of blood
pressure related to Mayer waves, are found in the power spectrum of the
heart rate [C. JULIEN. The enigma of Mayer waves: Facts and models.
Cardiovasc Res 70(1, 2006):12-21]. Even slower rhythms (<0.04 Hz),
thought to reflect temperature, blood volume, renin-angiotensin
regulation, as well as circadian rhythms, may also be present. The high
frequency respiratory component is primarily mediated by vagal activity,
and consequently, high frequency spectral power is often used as an index
of cardiac parasympathetic tone. Low-frequency power can be a valid
indicator of cardiac sympathetic activity under certain conditions, with
the understanding that baroreceptor regulation of blood pressure can be
achieved through both sympathetic and parasympathetic pathways. However,
more elaborate indices of sympathetic and parasympathetic activity may
also be extracted from the variation in successive heart beat intervals
[U. Rajendra ACHARYA, K. Paul Joseph, N. Kannathal, Choo Min Lim and
Jasjit S. Suri. Heart rate variability: a review. Medical and Biological
Engineering and Computing 44(12, 2006), 1031-1051].
[0158] Electrodermal activity has historically been used as a preferred
index of sympathetic tone, but it now competes with the use of heart rate
variability in that regard. Both heart rate and electrodermal activity
are controlled in part by neural pathways involving, for example, the
anterior cingulate cortex [Hugo D. CRITCHLEY, Christopher J. Mathias,
Oliver Josephs, et al. Human cingulate cortex and autonomic control:
converging neuroimaging and clinical evidence. Brain 126(2003):2139-2152;
Hugo D. CRITCHLEY. Electrodermal responses: what happens in the brain.
Neuroscientist 8(2, 2002):132-142]. Considering that neither
electrodermal nor heart rate variability indices of sympathetic activity
unambiguously characterize sympathetic activity within the central
nervous system, it is preferred that they both be measured. In fact,
additional noninvasive measures of sympathetic activity, such as
variability of QT intervals, are preferably measured as well [BOETTGER S,
Puta C, Yeragani V K, Donath L, Muller H J, Gabriel H H, Bar K J. Heart
rate variability, QT variability, and electrodermal activity during
exercise. Med Sci Sports Exerc 42(3, 2010):443-448].
[0159] Heart rate variability (HRV) biofeedback was introduced by Soviet
scientists during the measurement of autonomic function in cosmonauts.
The HRV biofeedback training involves instruction in breathing at an
identified frequency that is related to an optimal power band in the
heart rate variability Fourier spectrum. More specifically, biofeedback
training to increase the amplitude of respiratory sinus arrhythmia (RSA)
maximally increases the amplitude of heart rate oscillations only at
approximately 0.1 Hz. To perform this task people slow their breathing to
this rate to a point where resonance occurs between respiratory-induced
oscillations (RSA) and oscillations that naturally occur at this rate,
probably due in part to baroreflex activity. However, the preferred
breathing rate varies somewhat from individual to individual and must be
identified as a preliminary to the training. HRV biofeedback is said to
produce improvement in patients with asthma, chronic obstructive
pulmonary disease, cardiovascular disease and heart failure,
fibromyalgia, major depressive disorder and anxiety, and post-traumatic
stress disorder. Because the depth and rate of breathing are under
voluntary control of everyone but paralyzed individuals, HRV biofeedback
training has the virtue that it can be performed by almost anyone. In
fact, it may be argued that HRV biofeedback is not even a true
biofeedback method, but is instead simply a physiological maneuver that
evokes cardiopulmonary reflexes related to respiratory sinus arrhythmia
and a baroreflex [LEHRER P M, Vaschillo E, Vaschillo B. Resonant
frequency biofeedback training to increase cardiac variability: rationale
and manual for training. Appl Psychophysiol Biofeedback 25(3,
2000):177-191; LEHRER P, Carr R E, Smetankine A, Vaschillo E, Peper E,
Porges S, Edelberg R, Hamer R, Hochron S. Respiratory sinus arrhythmia
versus neck/trapezius EMG and incentive inspirometry biofeedback for
asthma: a pilot study. Appl Psychophysiol Biofeedback 22(2, 1997):95-109;
VASCHILLO E, Lehrer P, Rishe N, Konstantinov M. Heart rate variability
biofeedback as a method for assessing baroreflex function: a preliminary
study of resonance in the cardiovascular system. Appl Psychophysiol
Biofeedback 27(1, 2002):1-27; LEHRER P M, Vaschillo E, Vaschillo B, et
al. Heart rate variability biofeedback increases baroreflex gain and peak
expiratory flow. Psychosom Med 65(5, 2003):796-805; LEHRER P, Vaschillo
E, Lu S E, Eckberg D, Vaschillo B, Scardella A, Habib R. Heart rate
variability biofeedback: effects of age on heart rate variability,
baroreflex gain, and asthma. Chest 129(2, 2006):278-284; WHEAT A L,
Larkin K T. Biofeedback of heart rate variability and related physiology:
a critical review. Appl Psychophysiol Biofeedback 35(3, 2010):229-242;
PRINSLOO G E, Rauch H G, Karpul D, Derman W E. The effect of a single
session of short duration heart rate variability biofeedback on EEG: a
pilot study. Appl Psychophysiol Biofeedback 38(1, 2013):45-56].
[0160] In the present invention, vagus nerve stimulation may also be
performed in conjunction with HRV biofeedback, or it may be performed
alone to modulate heart rate variability if the biofeedback protocol
fails. Most investigations concerning the effect of vagus nerve
stimulation on heart rate variability are concerned with long-term effect
on particular categories of patients, rather than on acute effects [e.g.,
RONKAINEN E, Korpelainen J T, Heikkinen E, Myllyla V V, Huikuri H V,
Isojarvi J I. Cardiac autonomic control in patients with refractory
epilepsy before and during vagus nerve stimulation treatment: a one-year
follow-up study. Epilepsia 47(3, 2006):556-562; JANSEN K, Vandeput S,
Milosevic M, Ceulemans B, Van Huffel S, Brown L, Penders J, Lagae L.
Autonomic effects of refractory epilepsy on heart rate variability in
children: influence of intermittent vagus nerve stimulation. Dev Med
Child Neurol 53(12, 2011):1143-1149]. Nevertheless, there have been
several investigations concerning the acute effects of vagus nerve
stimulation on heart rate variability, which demonstrate that heart rate
variability can be used as an index of whether the vagus nerve is in fact
being stimulated. Most such studies demonstrate unambiguous heart rate
variability effects [KAMATH M V, Upton A R, Talalla A, Fallen E L. Effect
of vagal nerve electrostimulation on the power spectrum of heart rate
variability in man. Pacing Clin Electrophysiol 15(2, 1992):235-243; FREI
MG, Osorio I. Left vagus nerve stimulation with the neurocybernetic
prosthesis has complex effects on heart rate and on its variability in
humans. Epilepsia 42(8, 2001):1007-1016; STEMPER B, Devinsky O, Haendl T,
Welsch G, Hilz M J. Effects of vagus nerve stimulation on cardiovascular
regulation in patients with epilepsy. Acta Neurol Scand 117(4,
2008):231-236]. However, some investigators have also reported that vagus
nerve stimulation has no effect on heart rate variability, which FREI et
al attributed to methodological issues [SETTY A B, Vaughn B V, Quint S R,
Robertson K R, Messenheimer J A. Heart period variability during vagal
nerve stimulation. Seizure 7(3, 1998):213-217].
[0161] In contrast to the ease of performing HRV biofeedback, many, if not
most, individuals have difficulty learning to reliably control their EMG
or EEG using biofeedback, as noted above. GUGLIELMI et al describe
similar difficulties on the part of many individuals in controlling their
hand temperatures, and they attribute this in large measure to the
person-to-person lability of peripheral temperature responses [R. Sergio
GUGLIELMI and Alan H. Roberts. Volitional vasomotor lability and
vasomotor control. Biological Psychology 39(1994):29-44]. Similar
difficulties arise in the ability of individuals to control their
electro-dermal responses, which is also attributed to person-to-person
lability, much of which can in turn be attributed to genetic variability
among individuals [Andrew CRIDER. The electrodermal response: biofeedback
and individual difference studies. Applied Psychology 28(1, 1978): 37-48;
CRIDER A, Kremen W S, Xian H, Jacobson K C, Waterman B, Eisen S A, Tsuang
M T, Lyons M J. Stability, consistency, and heritability of electrodermal
response lability in middle-aged male twins. Psychophysiology 41(4,
2004):501-509; Michael E. DAWSON, Anne M. Schell, and Diane L. Filion.
The Electrodermal System. Chapter 7, pp. 159-181. In: Michael E. Dawson,
Anne M. Schell, Diane L. Filion, Gary G. Berntson, eds. Handbook of
Psychophysiology, Third edition. Cambridge: Cambridge University Press,
2007].
[0162] The present invention may use biofeedback alone, or biofeedback in
conjunction with stimulation of the vagus nerve, or it may use vagus
stimulation alone if the biofeedback protocol fails due to the inability
of the an individual to mentally control a physiological signal. When
vagus nerve stimulation is being performed, with or without biofeedback,
the disclosed system generally also uses feedback methods, as defined in
the engineering control theory of automatic control. For example,
irrespective of the use of biofeedback, feedback may be used in an
attempt to compensate for motion of the stimulator relative to the vagus
nerve and to avoid potentially dangerous situations, such as excessive
heart rate. As now described, with control theory methods, the parameters
of the vagus nerve stimulation may be changed automatically, depending on
the values of environmental signals or on physiological measurements that
are made, in attempt to maintain the values of the physiological signals
within predetermined ranges.
[0163] When stimulating the vagus nerve nonivasively, motion artifact
variability may often be attributable to the patient's breathing, which
involves contraction and associated change in geometry of the
sternocleidomastoid muscle that is situated close to the vagus nerve
(identified as 65 in FIGS. 9C and 10). Modulation of the stimulator
amplitude to compensate for this variability may be accomplished by
measuring the patient's respiratory phase, or more directly by measuring
movement of the stimulator, then using controllers (e.g., PID
controllers) that are known in the art of control theory, as now
described.
[0164] As shown in FIG. 1C, the physiological system receives input via a
vagus nerve from the vagus nerve stimulation device, including the
device's controlling electronic components that may be used to select or
set parameters for the stimulation protocol (amplitude, frequency, pulse
width, burst number, etc.) or alert the patient as to the need to use or
adjust the stimulator (i.e., an alarm). For example, the controller may
comprise the control unit 330 in FIG. 2. Feedback to the controller in
the schema shown in FIG. 1C is possible because physiological
measurements are made using sensors.
[0165] The physiological sensors used in the invention will ordinarily
include more sensors than those needed simply to construct the
biofeedback signal for a particular clinical application. This is because
the extra sensors may be needed for purposes such as compensating for
motion artifacts, or they may be needed in order to properly model the
time-course of the physiological signal that is to be controlled, as
described below.
[0166] The preferred sensors will include ones ordinarily used for
ambulatory monitoring. For example, the sensors may comprise those used
in conventional Holter and bedside monitoring applications, for
monitoring heart rate and variability, ECG, respiration depth and rate,
core temperature, hydration, blood pressure, brain function, oxygenation,
skin impedance, and skin temperature. The sensors may be embedded in
garments or placed in sports wristwatches, as currently used in programs
that monitor the physiological status of soldiers [G. A. SHAW, A. M.
Siegel, G. Zogbi, and T. P. Opar. Warfighter physiological and
environmental monitoring: a study for the U.S. Army Research Institute in
Environmental Medicine and the Soldier Systems Center. MIT Lincoln
Laboratory, Lexington Mass. 1 Nov. 2004, pp. 1-141]. The ECG sensors
should be adapted to the automatic extraction and analysis of particular
features of the ECG, for example, indices of P-wave morphology, as well
as heart rate variability indices of parasympathetic and sympathetic
tone. Measurement of respiration using noninvasive inductive
plethysmography, mercury in silastic strain gauges or impedance
pneumography is particularly advised, in order to account for the effects
of respiration on the heart. A noninvasive accelerometer may also be
included among the ambulatory sensors, in order to identify motion
artifacts. An event marker may also be included in order for the patient
to mark relevant circumstances and sensations.
[0167] For brain monitoring, the sensors may comprise ambulatory EEG
sensors [CASSON A, Yates D, Smith S, Duncan J, Rodriguez-Villegas E.
Wearable electroencephalography. What is it, why is it needed, and what
does it entail? IEEE Eng Med Biol Mag. 29(3, 2010):44-56] or optical
topography systems for mapping prefrontal cortex activation [ATSUMORI H,
Kiguchi M, Obata A, Sato H, Katura T, Funane T, Maki A. Development of
wearable optical topography system for mapping the prefrontal cortex
activation. Rev Sci Instrum. 2009 April; 80(4):043704, pp. 1-6]. Signal
processing methods, comprising not only the application of conventional
linear filters to the raw EEG data, but also the nearly real-time
extraction of non-linear signal features from the data, may be considered
to be a part of the EEG monitoring [D. Puthankattil SUBHA, Paul K.
Joseph, Rajendra Acharya U, and Choo Min Lim. EEG signal analysis: A
survey. J Med Syst 34(2010):195-212]. Such features would include EEG
bands (e.g., delta, theta, alpha, beta).
[0168] Detection of the phase of respiration may be performed
non-invasively by adhering a thermistor or thermocouple probe to the
patient's cheek so as to position the probe at the nasal orifice. Strain
gauge signals from belts strapped around the chest, as well as inductive
plethysmography and impedance pneumography, are also used traditionally
to generate a signal non-invasively that rises and falls as a function of
the phase of respiration. Respiratory phase may also be inferred from
movement of the sternocleidomastoid muscle that also causes movement of
the vagus nerve stimulator during breathing, measured using
accelerometers attached to the vagus nerve stimulator, as described
below. After digitizing such signals, the phase of respiration may be
determined using software such as "puka", which is part of PhysioToolkit,
a large published library of open source software and user manuals that
are used to process and display a wide range of physiological signals
[GOLDBERGER A L, Amaral L A N, Glass L, Hausdorff J M, Ivanov PCh, Mark R
G, Mietus J E, Moody G B, Peng C K, Stanley H E. PhysioBank,
PhysioToolkit, and PhysioNet: Components of a New Research Resource for
Complex Physiologic Signals. Circulation 101(23, 2000):e215-e220]
available from PhysioNet, M.I.T. Room E25-505A, 77 Massachusetts Avenue,
Cambridge, Mass. 02139]. In one embodiment of the present invention, the
control unit 330 in FIG. 2 contains an analog-to-digital converter to
receive such analog respiratory signals, and software for the analysis of
the digitized respiratory waveform resides within the control unit 330.
That software extracts turning points within the respiratory waveform,
such as end-expiration and end-inspiration, and forecasts future
turning-points, based upon the frequency with which waveforms from
previous breaths match a partial waveform for the current breath. The
control unit 330 then controls the impulse generator 310 in FIG. 2, for
example, to stimulate the selected nerve only during a selected phase of
respiration, such as all of inspiration or only the first second of
inspiration, or only the expected middle half of inspiration. In other
embodiments of the invention, the physiological or environmental signals
are transmitted wirelessly to the controller, as shown in FIG. 6. Some
such signals may be received by the docking station (e.g., ambient sound
signals) and other may be received within the stimulator housing (e.g.,
motion signals).
[0169] It may be therapeutically advantageous to program the control unit
330 in FIG. 2 to control the impulse generator 310 in such a way as to
temporally modulate stimulation by the electrodes, depending on the phase
of the patient's respiration. In patent application JP2008/081479A,
entitled Vagus nerve stimulation system, to YOSHIHOTO, a system is also
described for keeping the heart rate within safe limits. When the heart
rate is too high, that system stimulates a patient's vagus nerve, and
when the heart rate is too low, that system tries to achieve
stabilization of the heart rate by stimulating the heart itself, rather
than use different parameters to stimulate the vagus nerve. In that
disclosure, vagal stimulation uses an electrode, which is described as
either a surface electrode applied to the body surface or an electrode
introduced to the vicinity of the vagus nerve via a hypodermic needle.
That disclosure is unrelated to the biofeedback problems that are
addressed here, but it does consider stimulation during particular phases
of the respiratory cycle, for the following reason. Because the vagus
nerve is near the phrenic nerve (77 in FIG. 10), Yoshihoto indicates that
the phrenic nerve will sometimes be electrically stimulated along with
the vagus nerve. The present applicants have not experienced this
problem, so the problem may be one of a misplaced electrode. In any case,
the phrenic nerve controls muscular movement of the diaphragm, so
consequently, stimulation of the phrenic nerve causes the patient to
hiccup or experience irregular movement of the diaphragm, or otherwise
experience discomfort. To minimize the effects of irregular diaphragm
movement, Yoshihoto's system is designed to stimulate the phrenic nerve
(and possibly co-stimulate the vagus nerve) only during the inspiration
phase of the respiratory cycle and not during expiration. Furthermore,
the system is designed to gradually increase and then decrease the
magnitude of the electrical stimulation during inspiration (notably
amplitude and stimulus rate) so as to make stimulation of the phrenic
nerve and diaphragm gradual.
[0170] Furthermore, as an option in the present invention, parameters of
the stimulation may be modulated by the control unit 330 to control the
impulse generator 310 in such a way as to temporally modulate stimulation
by the electrodes, so as to achieve and maintain the heart rate within
safe or desired limits. In that case, the parameters of the stimulation
are individually raised or lowered in increments (power, frequency,
etc.), and the effect as an increased, unchanged, or decreased heart rate
is stored in the memory of the control unit 330. When the heart rate
changes to a value outside the specified range, the control unit 330
automatically resets the parameters to values that had been recorded to
produce a heart rate within that range, or if no heart rate within that
range has yet been achieved, it increases or decreases parameter values
in the direction that previously acquired data indicate would change the
heart rate in the direction towards a heart rate in the desired range.
Similarly, the arterial blood pressure is also recorded non-invasively in
an embodiment of the invention (e.g, with a wrist tonometer), and the
control unit 330 extracts the systolic, diastolic, and mean arterial
blood pressure from the blood pressure waveform. The control unit 330
will then control the impulse generator 310 in such a way as to
temporally modulate nerve stimulation by the electrodes, in such a way as
to achieve and maintain the blood pressure within predetermined safe or
desired limits, by the same method that was indicated above for the heart
rate.
[0171] Let the measured output variables from physiological sensors of the
system in FIG. 1 be denoted by y.sub.i (i=1 to Q); let the desired
(reference or setpoint) values of y.sub.i be denoted by r.sub.i and let
the controller's output via the stimulator consist of variables u.sub.j
(j=1 to P), which are also the input to the vagus nerve and other
biological entities. The objective is for a controller to select the
output from the stimulator, i.e. input to the body, (u.sub.j) in such a
way that the physiological signal output variables (or a subset of them)
closely follows the reference signals r.sub.i. Thus, it is intended that
the control error e.sub.i=r.sub.i-y.sub.i be small, even if there is
environmental input or noise to the system. In what follows, consider the
error function e.sub.i=r.sub.i-y.sub.i to be the sensed physiological
input to the control unit 330 in FIG. 2 (i.e., the reference signals are
integral to the controller, which subtracts the measured system values
from them to construct the control error signal). The controller will
also receive a set of measured environmental signals v.sub.k (k=1 to R),
which also act upon the system as shown in FIG. 1C. The patient's
response to biofeedback may be considered to be a type of environmental
input. During the initial, preliminary measurements, biofeedback is not
performed, but it may also be included during subsequent attempts to tune
and model the entire system.
[0172] As a first example of the use of feedback to control the system,
consider the problem of adjusting the input u(t) to the body (i.e.,
output from the controller as applied to the body via the impulse
generator) in order to compensate for motion artifacts. Nerve activation
is generally a function of the second spatial derivative of the
extracellular potential along the nerve's axon, which would be changing
as the position of the stimulator varies relative to the axon [F. RATTAY.
The basic mechanism for the electrical stimulation of the nervous system.
Neuroscience 89 (2, 1999):335-346]. Such motion artifact can be due to
movement by the patient (e.g., neck movement) or movement within the
patient (e.g. sternocleidomastoid muscle contraction associated with
respiration), or it can be due to movement of the stimulator relative to
the body (slippage or drift). Thus, one expects that because of such
undesired or unavoidable motion, there will usually be some error (e=r-y)
in the intended (r) versus actual (y) sensor values that needs continuous
adjustment.
[0173] Accelerometers can be used to detect all these types of movement,
using for example, Model LSM330DL from STMicroelectronics, 750 Canyon Dr
#300 Coppell, Tex. 75019. In one embodiment, one or more accelerometer is
attached to the patient's neck, and one or more accelerometer is attached
to the head(s) of the stimulator in the vicinity of where the stimulator
contacts the patient. Because the temporally integrated outputs of the
accelerometers provide a measurement of the current position of each
accelerometer, the combined accelerometer outputs make it possible to
measure any movement of the stimulator relative to the underlying tissue.
[0174] The location of the vagus nerve underlying the stimulator may be
determined preliminarily by placing an ultrasound probe at the location
where the center of the stimulator will be placed [KNAPPERTZ V A, Tegeler
C H, Hardin S J, McKinney W M. Vagus nerve imaging with ultrasound:
anatomic and in vivo validation. Otolaryngol Head Neck Surg 118(1,
1998):82-5]. The ultrasound probe is configured to have the same shape as
the stimulator, including the attachment of one or more accelerometer. As
part of the preliminary protocol, the patient with accelerometers
attached is then instructed or helped to perform neck movements, breathe
deeply so as to contract the sternocleidomastoid muscle, and generally
simulate possible motion that may accompany prolonged stimulation with
the stimulator. This would include possible slippage or movement of the
stimulator relative to an initial position on the patient's neck. While
these movements are being performed, the accelerometers are acquiring
position information, and the corresponding location of the vagus nerve
is determined from the ultrasound image. With these preliminary data, it
is then possible to infer the location of the vagus nerve relative to the
stimulator, given only the accelerometer data during a stimulation
session, by interpolating between the previously acquired vagus nerve
positional data as a function of accelerometer position data.
[0175] For any given position of the stimulator relative to the vagus
nerve, it is also possible to infer the amplitude of the electric field
that it produces in the vicinity of the vagus nerve. This is done by
calculation or by measuring the electric field that is produced by the
stimulator as a function of depth and position within a phantom that
simulates the relevant bodily tissue [Francis Marion MOORE. Electrical
Stimulation for pain suppression: mathematical and physical models.
Thesis, School of Engineering, Cornell University, 2007; Bartosz SAWICKI,
Robert Szmurto, Przemystaw Ptonecki, Jacek Starzy ski, Stanislaw
Wincenciak, Andrzej Rysz. Mathematical Modelling of Vagus Nerve
Stimulation. pp. 92-97 in: Krawczyk, A. Electromagnetic Field, Health and
Environment: Proceedings of EHE'07. Amsterdam, IOS Press, 2008]. Thus, in
order to compensate for movement, the controller may increase or decrease
the amplitude of the output from the stimulator (u) in proportion to the
inferred deviation of the amplitude of the electric field in the vicinity
of the vagus nerve, relative to its desired value.
[0176] A state-space representation, or model, of the entire system
consists of a set of first order differential equations of the form d
y.sub.i/dt=F.sub.i(t,{y.sub.i},{u.sub.j},{v.sub.k};{r.sub.i}), where t is
time and where in general, the rate of change of each variable y.sub.i is
a function (F.sub.i) of many other output variables as well as the input
and environmental signals. Classical control theory is concerned with
situations in which the functional form of F.sub.i is as a linear
combination of the state (y) and bodily input (u and v) variables, but in
which coefficients of the linear terms are not necessarily known in
advance. In this linear case, the differential equations may be solved
with linear transform (e.g., Laplace transform) methods, which convert
the differential equations into algebraic equations for straightforward
solution. Thus, for example, a single-input single-output system
(dropping the subscripts on variables) may have input from a controller
of the form:
u ( t ) = K p e ( t ) + K i .intg. 0 .tau.
e ( .tau. ) .tau. + K d s t
##EQU00001##
where the parameters for the controller are the proportional gain
(K.sub.p), the integral gain (K.sub.i) and the derivative gain (K.sub.d).
This type of controller, which forms a controlling input signal with
feedback using the error e=r-y, is known as a PID controller
(proportional-integral-derivative). Commercial versions of PID
controllers are available, and they are used in 90% of all control
applications.
[0177] Optimal selection of the parameters of the controller could be
through calculation, if the coefficients of the corresponding state
differential equation were known in advance. However, they are ordinarily
not known, so selection of the controller parameters (tuning) is
accomplished by experiments in which the error e either is or is not used
to form the system input (respectively, closed loop or open loop
experiments). In an open loop experiment, the input is increased in a
step (or random binary sequence of steps), and the system response is
measured. In a closed loop experiment, the integral and derivative gains
are set to zero, the proportional gain is increased until the system
starts to oscillate, and the period of oscillation is measured. Depending
on whether the experiment is open or closed loop, the selection of PID
parameter values may then be selected according to rules that were
described initially by Ziegler and Nichols. There are also many improved
versions of tuning rules, including some that can be implemented
automatically by the controller [LI, Y., Ang, K. H. and Chong, G. C. Y.
Patents, software and hardware for PID control: an overview and analysis
of the current art. IEEE Control Systems Magazine, 26 (1, 2006): 42-54;
Karl Johan .ANG.strom & Richard M. Murray. Feedback Systems: An
Introduction for Scientists and Engineers. Princeton N.J.: Princeton
University Press, 2008; Finn HAUGEN. Tuning of PID controllers (Chapter
10) In: Basic Dynamics and Control. 2009. ISBN 978-82-91748-13-9.
TechTeach, Enggravhogda 45, N-3711 Skien, Norway. http://techteach.no.,
pp. 129-155; Dingyu XUE, YangQuan Chen, Derek P. Atherton. PID controller
design (Chapter 6), In: Linear Feedback Control: Analysis and Design with
MATLAB. Society for Industrial and Applied Mathematics (SIAM). 3600
Market Street, 6th Floor, Philadelphia, Pa. (2007), pp. 183-235; Jan
JANTZEN, Tuning Of Fuzzy PID Controllers, Technical University of
Denmark, report 98-H 871, Sep. 30, 1998].
[0178] Although classical control theory works well for linear systems
having one or only a few system variables, special methods have been
developed for systems in which the system is nonlinear (i.e., the
state-space representation contains nonlinear differential equations), or
multiple input/output variables. Such methods are important for the
present invention because the physiological system to be controlled will
be generally nonlinear, and there will generally be multiple output
physiological signals. It is understood that those methods may also be
implemented in the control unit 330 shown in FIG. 2 [Torkel GLAD and
Lennart Ljung. Control Theory. Multivariable and Nonlinear Methods. New
York: Taylor and Francis, 2000; Zdzislaw BUBNICKI. Modern Control Theory.
Berlin: Springer, 2005].
[0179] The control unit 330 shown in FIG. 2 may also make use of
feed-forward methods [Coleman BROSILOW, Babu Joseph. Feedforward Control
(Chapter 9) In: Techniques of Model-Based Control. Upper Saddle River,
N.J.: Prentice Hall PTR, 2002. pp, 221-240]. Thus, the controller in FIG.
2 may be a type of predictive controller, methods for which have been
developed in other contexts as well, such as when a model of the system
is used to calculate future outputs of the system, with the objective of
choosing among possible inputs so as to optimize a criterion that is
based on future values of the system's output variables.
[0180] A mathematical model of the system is needed in order to perform
the predictions of system behavior, for purposes of including the
predictions in a feedforward control device. If the mechanisms of the
systems are not sufficiently understood in order to construct a
physiologically-based model, a black-box model may be used instead. Such
models comprise autoregressive models [Tim BOLLERSLEV. Generalized
autoregressive condiditional heteroskedasticity. Journal of Econometrics
31(1986):307-327], or those that make use of principal components [James
H. STOCK, Mark W. Watson. Forecasting with Many Predictors, In: Handbook
of Economic Forecasting. Volume 1, G. Elliott, C. W. J. Granger and A.
Timmermann, eds (2006) Amsterdam: Elsevier B. V, pp 515-554], Kalman
filters [Eric A. WAN and Rudolph van der Merwe. The unscented Kalman
filter for nonlinear estimation, In: Proceedings of Symposium 2000 on
Adaptive Systems for Signal Processing, Communication and Control
(AS-SPCC), IEEE, Lake Louise, Alberta, Canada, October, 2000, pp
153-158], wavelet transforms [O. RENAUD, J.-L. Stark, F. Murtagh.
Wavelet-based forecasting of short and long memory time series. Signal
Processing 48(1996):51-65], hidden Markov models [Sam ROWEIS and Zoubin
Ghahramani. A Unifying Review of Linear Gaussian Models. Neural
Computation 11(2, 1999): 305-345], or artificial neural networks
[Guoquiang ZHANG, B. Eddy Patuwo, Michael Y. Hu. Forecasting with
artificial neural networks: the state of the art. International Journal
of Forecasting 14(1998): 35-62].
[0181] For the present invention, the preferred black box model will be
one that makes use of support vector machines. A support vector machine
(SVM) is an algorithmic approach to the problem of classification within
the larger context of supervised learning. A number of classification
problems whose solutions in the past have been solved by multi-layer
back-propagation neural networks, or more complicated methods, have been
found to be more easily solvable by SVMs. In the present context, a
training set of physiological data will have been acquired that includes
whether or not a physiological variable is outside of its desired range.
Ordinarily, the variable will be one that is associated with the
patient's condition (e.g., blood pressure for a hypertensive individual,
or when biofeedback is being performed it may be the physiological signal
used to construct the biofeedback signal).
[0182] Thus, the classification of the patient's state is whether or not
the variable is out of range, and the data used to make the
classification consist of the remaining acquired physiological data,
evaluated at .DELTA. time units prior to the time at which a forecast of
the patient's status is to be made. Accordingly, the SVM is trained to
forecast .DELTA. time units into the future, where the time of the future
forecast .DELTA. is selected by the user. The forecast consists of
whether the variable is out of range, and optionally the predicted values
of any or all of the physiological variables that are being sensed. After
training the SVM, it is implemented as part of the controller. If
.DELTA.=0 and the signal being forecast is the one use to construct a
biofeedback signal, then the signal is simply the ordinary biofeedback
signal. However, when .DELTA.>0, the signal presented exteroceptively
to the patient can correspond to a predicted, future value of the
physiological variable. In that case, the system is effectively used for
biofeedforward control, rather than for biofeedback control. Then, the
patient can learn to respond consciously to what the signal is predicted
to become, rather than to what it currently is. Just as an anticipatory
response is useful for muscular systems such as when attempting to grasp
a moving rather than stationary object, then so too, the biofeedforward
control is useful for control of the autonomic nervous system when it is
experiencing significant time-varying fluctuations [Christopher J. C.
BURGES. A tutorial on support vector machines for pattern recognition.
Data Mining and Knowledge Discovery 2(1998), 121-167; J. A. K. Suykens,
J. Vandewalle, B. De Moor. Optimal Control by Least Squares Support
Vector Machines. Neural Networks 14 (2001):23-35; Sapankevych, N. and
Sankar, R. Time Series Prediction Using Support Vector Machines: A
Survey. IEEE Computational Intelligence Magazine 4(2, 2009): 24-38;
Press, W H; Teukolsky, S A; Vetterling, W T; Flannery, B P (2007).
Section 16.5. Support Vector Machines. In: Numerical Recipes: The Art of
Scientific Computing (3rd ed.). New York: Cambridge University Press].
[0183] A disclosure of the use of such feedback and feedforward methods to
forecast and avert the onset of many types of medical crises was made in
the co-pending, commonly assigned patent application U.S. Ser. No.
13/655,716 (publication US20130066395), entitled Nerve stimulation
methods for averting imminent onset or episode of a disease, to SIMON et
al, which is hereby incorporated by reference. The medical crises
comprise an asthma attack, epileptic seizure, attacks of migraine
headache, transient ischemic attack or stroke, onset of atrial
fibrillation, myocardial infarction, onset of ventricular fibrillation or
tachycardia, panic attack, and attacks of acute depression. The present
invention extends that disclosure to allow the additional use of
biofeedback, as shown in FIG. 1C.
[0184] An application of that previous disclosure, in the context of the
present invention, is as follows. When the physiological system has been
mathematically modeled first without the use of biofeedback, the model
provides an estimate of the temporal behavior of the system when it is
free from conscious control by the individual whose physiological
properties are being measured. When biofeedback is subsequently
incorporated into the methods as shown in FIG. 1C, then to the extent
that the forecasted behavior of the physiological system deviates from
what the model predicts, that quantitative deviation may be attributed in
part to how the individual is consciously trying to modulate the
physiological system. In the previous discussion surrounding FIG. 1C, it
was described how vagus nerve stimulation can be used to amplify or
enhance the conscious control of the system, by first allowing the
individual to attempt biofeedback by itself, then using the device to
sense the direction that the individual is trying to move the
physiological variable and amplify that effect by stimulating the vagus
nerve to move the variable even more. The mathematical model of the
system described above may be used for other situations, in which both
biofeedback and automatic control are being performed simultaneously. In
those cases, the intentions of the individual may be inferred from the
disclosed device as corresponding to the deviation of the physiological
variable from what the model predicts, taking into account the standard
deviation of the model's forecasting capabilities. The stimulator may
then be programmed to stimulate the vagus nerve in such a way as to
amplify or enhance the inferred intentions of the individual, when
biofeedback and automatic control are used simultaneously.
[0185] Selection of the Electrical Stimulation Waveform
[0186] In the present invention, electrical stimulation of the vagus nerve
and/or the skin results secondarily in the stimulation of regions of the
brain that are involved in autonomic regulation and conscious action.
Selection of stimulation waveform parameters to preferentially modulate
particular regions of the brain may be done empirically, wherein a set of
electrical stimulation waveform parameters is chosen (amplitude,
frequency, pulse width, etc.), and the responsive region of the brain is
measured using fMRI or a related imaging method [CHAE J H, Nahas Z,
Lomarev M, Denslow S, Lorberbaum J P, Bohning D E, George M S. A review
of functional neuroimaging studies of vagus nerve stimulation (VNS). J
Psychiatr Res. 37(6, 2003):443-455; CONWAY C R, Sheline Y I, Chibnall J
T, George M S, Fletcher J W, Mintun M A. Cerebral blood flow changes
during vagus nerve stimulation for depression. Psychiatry Res. 146(2,
2006):179-84]. Thus, by performing the imaging with different sets of
stimulation parameters, a database may be constructed, such that the
inverse problem of selecting parameters to match a particular selected
brain region may be solved by consulting the database.
[0187] However, there may be significant variation between individuals in
regards to the correspondence between stimulation parameters and the
associated brain structures that are activated. Furthermore, it may be
impractical to perform fMRI imaging on each individual who is to be
trained or treated by the disclosed invention. The individualized
selection of parameters for the nerve stimulation protocol will in any
case involve some trial and error, in order to obtain a beneficial
response without the sensation of skin pain or muscle twitches. The
parameters may also have to be updated periodically to compensate for any
adaptation on the part of the patient's nervous system to the electrical
stimulation. In addition, the selection of parameter values may involve
tuning and modeling as understood in control theory, as described in the
previous section. It is also understood that to some extent, parameters
may also be varied randomly in order to simulate normal physiological
variability, thereby possibly inducing a beneficial response in the
patient [BUCHMAN T G. Nonlinear dynamics, complex systems, and the
pathobiology of critical illness. Curr Opin Crit Care 10(5,
2004):378-82].
[0188] With regard to stimulating the patient's skin to construct a
biofeedback signal, many stimulation waveforms that have been tried in
connection with electro-tactile communication devices may also be used
for the present invention [R. H. GIBSON. Electrical stimulation of pain
and touch. pp. 223-261. In: D. R. Kenshalo, ed. The Skin Senses.
Springfield, Ill.: Charles C Thomas, 1968; Erich A. PFEIFFER. Electrical
stimulation of sensory nerves with skin electrodes for research,
diagnosis, communication and behavioral conditioning: A survey. Medical
and Biological Engineering. 6(6, 1968):637-651; Kahori KITA, Kotaro
Takeda, Rieko Osu, Sachiko Sakata, Yohei Otaka, Junichi Ushiba. A Sensory
feedback system utilizing cutaneous electrical stimulation for stroke
patients with sensory loss. Proc. 2011 IEEE International Conference on
Rehabilitation Robotics, Zurich, Switzerland, Jun. 29-Jul. 1, 2011,
2011:5975489, pp 1-6; Mark R. PRAUSNITZ. The effects of electric current
applied to skin: A review for transdermal drug delivery. Advanced Drug
Delivery Reviews 18 (1996) 395-425].
[0189] For example, let stimL be the lower threshold of the skin
stimulation current, defined for each patient as the lowest current at
which he or she can feel stimulation to the skin. Let stimU be the upper
threshold of the skin stimulation current, defined as a fixed percentage
(e.g. 95%) of the magnitude of current to the skin that first begins to
materially stimulate the vagus nerve, as evidenced by any of the methods
described in commonly assigned and co-pending patent application U.S.
Ser. No. 13/872,116, entitled DEVICES AND METHODS FOR MONITORING
NON-INVASIVE VAGUS NERVE STIMULATION, to SIMON et al., which is hereby
incorporated by reference. StimU may be measured when the waveform used
to stimulate the vagus nerve itself is simultaneously applied as a
superimposed signal (see below), but in which the vagus stimulation
waveform has an amplitude that is also set just under the one at which
the vagus nerve is first materially stimulated.
[0190] Let ipL and ipU be the minimum and maximum values of the sensed
physiological variable that are to be used for biofeedback, respectively.
Each of these factors (stimL, stimU, ipL and ipU) is measured or decided
shortly prior to the therapy. Let stim(n) be defined as a magnification
factor of the current at the n-th sampling of the physiological signal
that is used to construct the biofeedback signal, which then has the
value ip(n). Then, let stim(n)=stimL when ip(n)<ipL; let stim(n)=stimU
when ip(n)>ipU, and let stim(n) vary linearly between stimL and stimU
as a function of ip(n), when ip(n) is between or at the endpoints ipL and
ipU.
[0191] In this embodiment, the electrical biofeedback signal to the skin
will be proportional to stim(n) multiplied by f(t), where f(t) is a
monophasic rectangular electric pulse sequence having a repeat interval
of, for example, 10 milliseconds and duration of 300 microseconds. The
interval and pulse duration may be optimized for each patient, so that
the psychological sensation of the cutaneous biofeedback is maximized for
a given total skin current, but without any sensation of pain or
discomfort.
[0192] A digital biofeedback signal to the skin may also be used. For
example, ipL, ipU, and ipL+(ipU-ipL)/2 may be used as the only three
levels that are applied to the skin, and each of them may have a pulse
train duration of, e.g., 0.5, 1, or 2 seconds, for a total of 9 possible
signal train combinations. The pulse train that is actually applied at
any instant may then be selected according to the measured physiological
signal, with higher amplitude and longer pulse trains corresponding to
increasing values of the physiological signal.
[0193] The selection of a waveform to stimulate a nerve that lies deep
under the skin, such as a vagus nerve, is a more difficult problem
because the selection must be made so as not to cause skin pain or muscle
twitches. The waveform for stimulating the deep nerve will generally be
superimposed upon the cutaneous biofeedback signal described above. FIG.
11A illustrates an exemplary electrical voltage/current profile for a
stimulating, blocking and/or modulating impulse applied to a portion or
portions of selected nerve (e.g. vagus nerve) in accordance with an
embodiment of the present invention. For the preferred embodiment, the
voltage and current refer to those that are non-invasively produced
within the patient by the electrodes (or stimulator coils). As shown, a
suitable electrical voltage/current profile 400 for the blocking and/or
modulating impulse 410 to the portion or portions of a nerve may be
achieved using pulse generator 310 in FIG. 2. In a preferred embodiment,
the pulse generator 310 may be implemented using a power source 320 and a
control unit 330 having, for instance, a processor, a clock, a memory,
etc., to produce a pulse train 420 to the electrodes 340 that deliver the
stimulating, blocking and/or modulating impulse 410 to the nerve. The
parameters of the modulation signal 400, such as the frequency,
amplitude, duty cycle, pulse width, pulse shape, etc., are preferably
programmable. An external communication device may modify the pulse
generator programming to facilitate treatment.
[0194] A device such as that disclosed in patent publication No.
US2005/0216062 may be employed to generate the stimulation waveform. That
patent publication discloses a multifunctional electrical stimulation
(ES) system adapted to yield output signals for effecting electromagnetic
or other forms of electrical stimulation for a broad spectrum of
different biological and biomedical applications, which produce an
electric field pulse in order to non-invasively stimulate nerves. The
system includes an ES signal stage having a selector coupled to a
plurality of different signal generators, each producing a signal having
a distinct shape, such as a sine wave, a square or a saw-tooth wave, or
simple or complex pulse, the parameters of which are adjustable in regard
to amplitude, duration, repetition rate and other variables. Examples of
the signals that may be generated by such a system are described in a
publication by LIBOFF [A. R. LIBOFF. Signal shapes in electromagnetic
therapies: a primer. pp. 17-37 in: Bioelectromagnetic Medicine (Paul J.
Rosch and Marko S. Markov, eds.). New York: Marcel Dekker (2004)]. The
signal from the selected generator in the ES stage is fed to at least one
output stage where it is processed to produce a high or low voltage or
current output of a desired polarity whereby the output stage is capable
of yielding an electrical stimulation signal appropriate for its intended
application. Also included in the system is a measuring stage which
measures and displays the electrical stimulation signal operating on the
substance being treated, as well as the outputs of various sensors which
sense prevailing conditions prevailing in this substance, whereby the
user of the system can manually adjust the signal, or have it
automatically adjusted by feedback, to provide an electrical stimulation
signal of whatever type the user wishes, who can then observe the effect
of this signal on the entity being treated.
[0195] The stimulating and/or modulating impulse signal 410 in FIG. 11A
preferably has a frequency, an amplitude, a duty cycle, a pulse width, a
pulse shape, etc. selected to influence the therapeutic result, namely,
stimulating and/or modulating some or all of the transmissions of the
selected nerve. For example, the frequency may be about 1 Hz or greater,
such as between about 15 Hz to 100 Hz, more preferably around 25 Hz. The
modulation signal may have a pulse width selected to influence the
therapeutic result, such as about 1 microseconds to about 1000
microseconds. For example, the electric field induced or produced by the
device within tissue in the vicinity of a nerve may be about 5 to 600
V/m, preferably less than 100 V/m, and even more preferably less than 30
V/m. The gradient of the electric field may be greater than 2 V/m/mm.
More generally, the stimulation device produces an electric field in the
vicinity of the nerve that is sufficient to cause the nerve to depolarize
and reach a threshold for action potential propagation, which is
approximately 8 V/m at 1000 Hz. The modulation signal may have a peak
voltage amplitude selected to influence the therapeutic result, such as
about 0.2 volts or greater, such as about 0.2 volts to about 40 volts.
[0196] An objective of the disclosed stimulator is to provide both nerve
fiber selectivity and spatial selectivity. Spatial selectivity may be
achieved in part through the design of the electrode (or magnetic coil)
configuration, and nerve fiber selectivity may be achieved in part
through the design of the stimulus waveform, but designs for the two
types of selectivity are intertwined. This is because, for example, a
waveform may selectively stimulate only one of two nerves whether they
lie close to one another or not, obviating the need to focus the
stimulating signal onto only one of the nerves [GRILL W and Mortimer J T.
Stimulus waveforms for selective neural stimulation. IEEE Eng. Med. Biol.
14 (1995): 375-385]. These methods complement others that are used to
achieve selective nerve stimulation, such as the use of local anesthetic,
application of pressure, inducement of ischemia, cooling, use of
ultrasound, graded increases in stimulus intensity, exploiting the
absolute refractory period of axons, and the application of stimulus
blocks [John E. SWETT and Charles M. Bourassa. Electrical stimulation of
peripheral nerve. In: Electrical Stimulation Research Techniques, Michael
M. Patterson and Raymond P. Kesner, eds. Academic Press. (New York, 1981)
pp. 243-295].
[0197] To date, the selection of stimulation waveform parameters for vagus
nerve stimulation has been highly empirical, in which the parameters are
varied about some initially successful set of parameters, in an effort to
find an improved set of parameters for each patient. A more efficient
approach to selecting stimulation parameters might be to select a
stimulation waveform that mimics electrical activity in the anatomical
regions that one is attempting activate indirectly, in an effort to
entrain the naturally occurring electrical waveform, as suggested in
patent number U.S. Pat. No. 6,234,953, entitled Electrotherapy device
using low frequency magnetic pulses, to THOMAS et al. and application
number US20090299435, entitled Systems and methods for enhancing or
affecting neural stimulation efficiency and/or efficacy, to GLINER et al.
One may also vary stimulation parameters iteratively, in search of an
optimal setting [U.S. Pat. No. 7,869,885, entitled Threshold optimization
for tissue stimulation therapy, to BEGNAUD et al]. However, some
stimulation waveforms, such as those described below, are discovered by
trial and error, and then deliberately improved upon.
[0198] Invasive nerve stimulation typically uses square wave pulse
signals. However, Applicant found that square waveforms are not ideal for
non-invasive stimulation of the vagus nerve because they produce
excessive pain. Pre-pulses and similar waveform modifications have been
suggested as methods to improve selectivity of nerve stimulation
waveforms, but Applicant did not find them ideal [Aleksandra VUCKOVIC,
Marco Tosato and Johannes J Struijk. A comparative study of three
techniques for diameter selective fiber activation in the vagal nerve:
anodal block, depolarizing prepulses and slowly rising pulses. J. Neural
Eng. 5 (2008): 275-286; Aleksandra VUCKOVIC, Nico J. M. Rijkhoff, and
Johannes J. Struijk. Different Pulse Shapes to Obtain Small Fiber
Selective Activation by Anodal Blocking--A Simulation Study. IEEE
Transactions on Biomedical Engineering 51(5, 2004):698-706; Kristian
HENNINGS. Selective Electrical Stimulation of Peripheral Nerve Fibers:
Accommodation Based Methods. Ph.D. Thesis, Center for Sensory-Motor
Interaction, Aalborg University, Aalborg, Denmark, 2004].
[0199] Applicant also found that stimulation waveforms consisting of
bursts of square pulses are not ideal for non-invasive stimulation [M. I.
JOHNSON, C. H. Ashton, D. R. Bousfield and J. W. Thompson. Analgesic
effects of different pulse patterns of transcutaneous electrical nerve
stimulation on cold-induced pain in normal subjects. Journal of
Psychosomatic Research 35 (2/3, 1991):313-321; U.S. Pat. No. 7,734,340,
entitled Stimulation design for neuromodulation, to De Ridder]. However,
bursts of sinusoidal pulses were determined to be a preferred stimulation
waveform, as shown in FIGS. 11B and 11C. As seen there, individual
sinusoidal pulses have a period of tau, and a burst consists of N such
pulses. This is followed by a period with no signal (the inter-burst
period). The pattern of a burst followed by silent inter-burst period
repeats itself with a period of T. For example, the sinusoidal period tau
may be 200 microseconds; the number of pulses per burst may be N=5; and
the whole pattern of burst followed by silent inter-burst period may have
a period of T=40000 microseconds, which is comparable to 25 Hz
stimulation (a much smaller value of T is shown in FIG. 11C to make the
bursts discernable). When these exemplary values are used for T and tau,
the waveform contains significant Fourier components at higher
frequencies (1/200 microseconds=5000/sec), as compared with those
contained in transcutaneous nerve stimulation waveforms, as currently
practiced.
[0200] Applicant is unaware of such a waveform having been used with vagus
nerve stimulation, but a similar waveform has been used to stimulate
muscle as a means of increasing muscle strength in elite athletes.
However, for the muscle strengthening application, the currents used (200
mA) may be very painful and two orders of magnitude larger than what are
disclosed herein. Furthermore, the signal used for muscle strengthening
may be other than sinusoidal (e.g., triangular), and the parameters tau,
N, and T may also be dissimilar from the values exemplified above [A.
DELITTO, M. Brown, M. J. Strube, S. J. Rose, and R. C. Lehman. Electrical
stimulation of the quadriceps femoris in an elite weight lifter: a single
subject experiment. Int J Sports Med 10(1989):187-191; Alex R WARD,
Nataliya Shkuratova. Russian Electrical Stimulation: The Early
Experiments. Physical Therapy 82 (10, 2002): 1019-1030; Yocheved LAUFER
and Michal Elboim. Effect of Burst Frequency and Duration of
Kilohertz-Frequency Alternating Currents and of Low-Frequency Pulsed
Currents on Strength of Contraction, Muscle Fatigue, and Perceived
Discomfort. Physical Therapy 88 (10, 2008):1167-1176; Alex R WARD.
Electrical Stimulation Using Kilohertz-Frequency Alternating Current.
Physical Therapy 89 (2, 2009):181-190; J. PETROFSKY, M. Laymon, M.
Prowse, S. Gunda, and J. Batt. The transfer of current through skin and
muscle during electrical stimulation with sine, square, Russian and
interferential waveforms. Journal of Medical Engineering and Technology
33 (2, 2009): 170-181; U.S. Pat. No. 4,177,819, entitled Muscle
stimulating apparatus, to KOFSKY et al]. Burst stimulation has also been
disclosed in connection with implantable pulse generators, but wherein
the bursting is characteristic of the neuronal firing pattern itself
[U.S. Pat. No. 7,734,340 to DE RIDDER, entitled Stimulation design for
neuromodulation; application US20110184486 to DE RIDDER, entitled
Combination of tonic and burst stimulations to treat neurological
disorders]. By way of example, the electric field shown in FIGS. 11B and
11C may have an E.sub.max value of 17 V/m, which is sufficient to
stimulate the nerve but is significantly lower than the threshold needed
to stimulate surrounding muscle.
[0201] High frequency electrical stimulation is also known in the
treatment of back pain at the spine [Patent application US20120197369,
entitled Selective high frequency spinal cord modulation for inhibiting
pain with reduced side effects and associated systems and methods, to
ALATARIS et al.; Adrian AL KAISY, Iris Smet, and Jean-Pierre Van Buyten.
Analgeia of axial low back pain with novel spinal neuromodulation. Poster
presentation #202 at the 2011 meeting of The American Academy of Pain
Medicine, held in National Harbor, Md., Mar. 24-27, 2011].
[0202] Those methods involve high-frequency modulation in the range of
from about 1.5 KHz to about 50 KHz, which is applied to the patient's
spinal cord region. However, such methods are different from the present
invention because, for example, they is invasive; they do not involve a
bursting waveform, as in the present invention; they necessarily involve
A-delta and C nerve fibers and the pain that those fibers produce (see
below), whereas the present invention does not; they may involve a
conduction block applied at the dorsal root level, whereas the present
invention may stimulate action potentials without blocking of such action
potentials; and/or they involve an increased ability of high frequency
modulation to penetrate through the cerebral spinal fluid, which is not
relevant to the present invention. In fact, a likely explanation for the
reduced back pain that is produced by their use of frequencies from 10 to
50 KHz is that the applied electrical stimulus at those frequencies
causes permanent damage to the pain-causing nerves, whereas the present
invention involves only reversible effects [LEE RC, Zhang D, Hannig J.
Biophysical injury mechanisms in electrical shock trauma. Annu Rev Biomed
Eng 2(2000):477-509].
[0203] Consider now which nerve fibers may be stimulated by the
non-invasive vagus nerve stimulation waveform shown in FIGS. 11B and 11C.
A vagus nerve in man consists of over 100,000 nerve fibers (axons),
mostly organized into groups. The groups are contained within fascicles
of varying sizes, which branch and converge along the nerve. Under normal
physiological conditions, each fiber conducts electrical impulses only in
one direction, which is defined to be the orthodromic direction, and
which is opposite the antidromic direction. However, external electrical
stimulation of the nerve may produce action potentials that propagate in
orthodromic and antidromic directions. Besides efferent output fibers
that convey signals to the various organs in the body from the central
nervous system, the vagus nerve conveys sensory (afferent) information
about the state of the body's organs back to the central nervous system.
Some 80-90% of the nerve fibers in the vagus nerve are afferent (sensory)
nerves, communicating the state of the viscera to the central nervous
system.
[0204] The largest nerve fibers within a left or right vagus nerve are
approximately 20 .mu.m in diameter and are heavily myelinated, whereas
only the smallest nerve fibers of less than about 1 .mu.m in diameter are
completely unmyelinated. When the distal part of a nerve is electrically
stimulated, a compound action potential may be recorded by an electrode
located more proximally. A compound action potential contains several
peaks or waves of activity that represent the summated response of
multiple fibers having similar conduction velocities. The waves in a
compound action potential represent different types of nerve fibers that
are classified into corresponding functional categories, with approximate
diameters as follows: A-alpha fibers (afferent or efferent fibers, 12-20
.mu.m diameter), A-beta fibers (afferent or efferent fibers, 5-12 .mu.m),
A-gamma fibers (efferent fibers, 3-7 .mu.m), A-delta fibers (afferent
fibers, 2-5 .mu.m), B fibers (1-3 .mu.m) and C fibers (unmyelinated,
0.4-1.2 .mu.m). The diameters of group A and group B fibers include the
thickness of the myelin sheaths. It is understood that the anatomy of the
vagus nerve is developing in newborns and infants, which accounts in part
for the maturation of autonomic reflexes. Accordingly, it is also
understood that the parameters of vagus nerve stimulation in the present
invention are chosen in such a way as to account for this age-related
maturation [PEREYRA P M, Zhang W, Schmidt M, Becker L E. Development of
myelinated and unmyelinated fibers of human vagus nerve during the first
year of life. J Neurol Sci 110(1-2, 1992):107-113].
[0205] The waveform disclosed in FIG. 11 contains significant Fourier
components at high frequencies (e.g., 1/200 microseconds=5000/sec), even
if the waveform also has components at lower frequencies (e.g., 25/sec).
Transcutaneously, A-beta, A-delta, and C fibers are typically excited at
2000 Hz, 250 Hz, and 5 Hz, respectively, i.e., the 2000 Hz stimulus is
described as being specific for measuring the response of A-beta fibers,
the 250 Hz for A-delta fibers, and the 5 Hz for type C fibers [George D.
BAQUIS et al. TECHNOLOGY REVIEW: THE NEUROMETER CURRENT PERCEPTION
THRESHOLD (CPT). Muscle Nerve 22(Supplement 8, 1999): S247-S259].
Therefore, the high frequency component of the noninvasive stimulation
waveform will preferentially stimulate the A-alpha and A-beta fibers, and
the C fibers will be largely unstimulated.
[0206] However, the threshold for activation of fiber types also depends
on the amplitude of the stimulation, and for a given stimulation
frequency, the threshold increases as the fiber size decreases. The
threshold for generating an action potential in nerve fibers that are
impaled with electrodes is traditionally described by Lapicque or Weiss
equations, which describe how together the width and amplitude of
stimulus pulses determine the threshold, along with parameters that
characterize the fiber (the chronaxy and rheobase). For nerve fibers that
are stimulated by electric fields that are applied externally to the
fiber, as is the case here, characterizing the threshold as a function of
pulse amplitude and frequency is more complicated, which ordinarily
involves the numerical solution of model differential equations or a
case-by-case experimental evaluation [David BOINAGROV, Jim Loudin and
Daniel Palanker. Strength-Duration Relationship for Extracellular Neural
Stimulation: Numerical and Analytical Models. J Neurophysiol
104(2010):2236-2248].
[0207] For example, REILLY describes a model (the spatially extended
nonlinear nodal model or SENN model) that may be used to calculate
minimum stimulus thresholds for nerve fibers having different diameters
[J. Patrick REILLY. Electrical models for neural excitation studies.
Johns Hopkins APL Technical Digest 9(1, 1988): 44-59]. According to
REILLY's analysis, the minimum threshold for excitation of myelinated A
fibers is 6.2 V/m for a 20 .mu.m diameter fiber, 12.3 V/m for a 10 .mu.m
fiber, and 24.6 V/m for a 5 .mu.m diameter fiber, assuming a pulse width
that is within the contemplated range of the present invention (1 ms). It
is understood that these thresholds may differ slightly from those
produced by the waveform of the present invention as illustrated by
REILLY's figures, for example, because the present invention prefers to
use sinusoidal rather than square pulses. Thresholds for B and C fibers
are respectively 2 to 3 and 10 to 100 times greater than those for A
fibers [Mark A. CASTORO, Paul B. Yoo, Juan G. Hincapie, Jason J. Hamann,
Stephen B. Ruble, Patrick D. Wolf, Warren M. Grill. Excitation properties
of the right cervical vagus nerve in adult dogs. Experimental Neurology
227 (2011): 62-68]. If we assume an average A fiber threshold of 15 V/m,
then B fibers would have thresholds of 30 to 45 V/m and C fibers would
have thresholds of 150 to 1500 V/m. The present invention produces
electric fields at the vagus nerve in the range of about 6 to 100 V/m,
which is therefore generally sufficient to excite all myelinated A and B
fibers, but not the unmyelinated C fibers. In contrast, invasive vagus
nerve stimulators that have been used for the treatment of epilepsy have
been reported to excite C fibers in some patients [EVANS M S, Verma-Ahuja
S, Naritoku D K, Espinosa J A. Intraoperative human vagus nerve compound
action potentials. Acta Neurol Scand 110(2004): 232-238].
[0208] It is understood that although devices of the present invention may
stimulate A and B nerve fibers, in practice they may also be used so as
not to stimulate the A-delta) and B fibers. In particular, if the
stimulator amplitude has been increased to the point at which unwanted
side effects begin to occur, the operator of the device may simply reduce
the amplitude to avoid those effects. For example, vagal efferent fibers
responsible for bronchoconstriction have been observed to have conduction
velocities in the range of those of B fibers. In those experiments,
bronchoconstriction was only produced when B fibers were activated, and
became maximal before C fibers had been recruited [R. M. McALLEN and K.
M. Spyer. Two types of vagal preganglionic motoneurones projecting to the
heart and lungs. J. Physiol. 282(1978): 353-364]. Because proper
stimulation with the disclosed devices does not result in the side-effect
of bronchoconstriction, evidently the bronchoconstrictive B-fibers are
possibly not being activated when the amplitude is properly set. Also,
the absence of bradycardia or prolongation of PR interval suggests that
cardiac efferent B-fibers are not stimulated. Similarly, A-delta
afferents may behave physiologically like C fibers. Because stimulation
with the disclosed devices does not produce nociceptive effects that
would be produced by jugular A-delta fibers or C fibers, evidently the
A-delta fibers may not be stimulated when the amplitude is properly set.
[0209] The use of feedback to generate the modulation signal 400 in FIG.
11 may result in a signal that is not periodic, particularly if the
feedback is produced from sensors that measure naturally occurring,
time-varying aperiodic physiological signals from the patient (see FIG.
1). In fact, the absence of significant fluctuation in naturally
occurring physiological signals from a patient is ordinarily considered
to be an indication that the patient is in ill health. This is because a
pathological control system that regulates the patient's physiological
variables may have become trapped around only one of two or more possible
steady states and is therefore unable to respond normally to external and
internal stresses. Accordingly, even if feedback were not used to
generate the modulation signal 400, it may be useful to artificially
modulate the signal in an aperiodic fashion, in such a way as to simulate
fluctuations that would occur naturally in a healthy individual. Thus,
the noisy modulation of the stimulation signal may cause a pathological
physiological control system to be reset or undergo a non-linear phase
transition, through a mechanism known as stochastic resonance [B. SUKI,
A. Alencar, M. K. Sujeer, K. R. Lutchen, J. J. Collins, J. S. Andrade, E.
P. Ingenito, S. Zapperi, H. E. Stanley, Life-support system benefits from
noise, Nature 393 (1998) 127-128; W Alan C MUTCH, M Ruth Graham, Linda G
Girling and John F Brewster. Fractal ventilation enhances respiratory
sinus arrhythmia. Respiratory Research 2005, 6:41, pp. 1-9].
[0210] So, in one embodiment of the present invention, the modulation
signal 400 in FIG. 11, with or without feedback, will stimulate the
selected nerve fibers in such a way that one or more of the stimulation
parameters (power, frequency, and others mentioned herein) are varied by
sampling a statistical distribution having a mean corresponding to a
selected, or to a most recent running-averaged value of the parameter,
and then setting the value of the parameter to the randomly sampled
value. The sampled statistical distributions will comprise Gaussian and
1/f, obtained from recorded naturally occurring random time series or by
calculated formula. Parameter values will be so changed periodically, or
at time intervals that are themselves selected randomly by sampling
another statistical distribution, having a selected mean and coefficient
of variation, where the sampled distributions comprise Gaussian and
exponential, obtained from recorded naturally occurring random time
series or by calculated formula.
[0211] Selection of Stimulation Parameters to Activate or Suppress
Selected Resting State Networks of the Brain
[0212] FIG. 12 shows the location of the cervical stimulation as "Vagus
Nerve Stimulation," relative to its connections with other anatomical
structures that are potentially affected by the stimulation. In different
embodiments of the invention, various brain and brainstem structures are
preferentially modulated by the stimulation. Besides efferent output
fibers that convey signals to the various organs in the body from the
central nervous system, the vagus nerve conveys sensory (afferent)
information about the state of the body's organs back to the central
nervous system. Propagation of electrical signals in efferent and
afferent directions is indicated by arrows in FIG. 12. If communication
between structures is bidirectional, this is shown in FIG. 12 as a single
connection with two arrows, rather than showing the efferent and afferent
nerve fibers separately.
[0213] The vagus (or vagal) afferent nerve fibers arise from cell bodies
located in the vagal sensory ganglia. These ganglia take the form of
swellings found in the cervical aspect of the vagus nerve just caudal to
the skull. There are two such ganglia, termed the inferior and superior
vagal ganglia. They are also called the nodose and jugular ganglia,
respectively (See FIG. 12). The jugular (superior) ganglion is a small
ganglion on the vagus nerve just as it passes through the jugular foramen
at the base of the skull. The nodose (inferior) ganglion is a ganglion on
the vagus nerve located in the height of the transverse process of the
first cervical vertebra.
[0214] Vagal afferents traverse the brainstem in the solitary tract, with
some eighty percent of the terminating synapses being located in the
nucleus of the tractus solitarius (or nucleus tractus solitarii, nucleus
tractus solitarius, or NTS, see FIG. 12). The NTS projects to a wide
variety of structures in the central nervous system, such as the
amygdala, raphe nuclei, periaqueductal gray, nucleus
paragigantocellurlais, olfactory tubercule, locus ceruleus, nucleus
ambiguus and the hypothalamus. The NTS also projects to the parabrachial
nucleus, which in turn projects to the hypothalamus, the thalamus, the
amygdala, the anterior insula, and infralimbic cortex, lateral prefrontal
cortex, and other cortical regions [JEAN A. The nucleus tractus
solitarius: neuroanatomic, neurochemical and functional aspects. Arch Int
Physiol Biochim Biophys 99(5, 1991):A3-A52]. Such central projections are
discussed below in connection with interoception and resting state neural
networks.
[0215] With regard to vagal efferent nerve fibers, two vagal components
have evolved in the brainstem to regulate peripheral parasympathetic
functions. The dorsal vagal complex, consisting of the dorsal motor
nucleus and its connections (see FIG. 12), controls parasympathetic
function primarily below the level of the diaphragm (e.g. gut), while the
ventral vagal complex, comprised of the nucleus ambiguus and nucleus
retrofacial, controls functions primarily above the diaphragm in organs
such as the heart, thymus and lungs, as well as other glands and tissues
of the neck and upper chest, and specialized muscles such as those of the
esophageal complex. For example, the cell bodies for the preganglionic
parasympathetic vagal neurons that innervate the heart reside in the
nucleus ambiguus, which is relevant to potential cardiovascular side
effects that may be produced by vagus nerve stimulation.
[0216] Non-invasive stimulation of the cervical vagus nerve (nVNS) is a
novel technology for treating various central nervous system disorders,
primarily by stimulating specific afferent fibers of the vagus nerve to
modulate brain function. This technology has been demonstrated in animal
and human studies to treat a wide range of central nervous system
disorders including headache (chronic and acute cluster and migraine),
epilepsy, bronchoconstriction, anxiety disorders, depression, rhinitis,
fibromyalgia, irritable bowel syndrome, stroke, traumatic brain injury,
PTSD, Alzheimer's disease, autism, and others [See Cross Reference to
Related Applications for the corresponding co-pending and commonly
assigned applications, which are hereby incorporated by reference]. Many
of these conditions have also been treated with limited efficacy using
biofeedback, and the combined use of biofeedback with vagus nerve
stimulation is intended to produce improved clinical results.
[0217] Applicants have discovered that as little as two-minutes of vagus
nerve stimulation produces effects that may last up to 8 hours or longer,
depending on the type and severity of indication. Broadly speaking, there
are three components to the effects of nVNS on the brain. The strongest
effect occurs during the two minute stimulation and results in
significant changes in brain function that can be clearly seen as acute
changes in autonomic function (e.g. measured using pupillometry, heart
rate variability, galvanic skin response, or evoked potential) and
activation and inhibition of various brain regions as shown in fMRI
imaging studies. The second effect, of moderate intensity, lasts for 15
to 180 minutes after stimulation. Animal studies have shown changes in
neurotransmitter levels in various parts of the brain that persist for
several hours. The third effect, of mild intensity, lasts up to 8 hours
and is responsible for the long lasting alleviation of symptoms seen
clinically and, for example, in animal models of migraine headache. Thus,
depending on the medical indication, whether it is a chronic or acute
treatment, and the natural history of the disease, different treatment
protocols may be used.
[0218] The vagus nerve stimulation may have excitatory and inhibitory
effects. Some circuits involved in inhibition are illustrated in FIG. 12.
Excitatory nerves within the dorsal vagal complex generally use glutamate
as their neurotransmitter. To inhibit neurotransmission within the dorsal
vagal complex, the present invention makes use of the bidirectional
connections that the nucleus of the solitary tract (NTS) has with
structures that produce inhibitory neurotransmitters, or it makes use of
connections that the NTS has with the hypothalamus, which in turn
projects to structures that produce inhibitory neurotransmitters. The
inhibition is produced as the result of the stimulation waveforms that
are disclosed in the previous section. Thus, acting in opposition to
glutamate-mediated activation by the NTS of the area postrema and dorsal
motor nucleus are: GABA, and/or serotonin, and/or norepinephrine from the
periaqueductal gray, raphe nucei, and locus coeruleus, respectively. FIG.
12 shows how those excitatory and inhibitory influences combine to
modulate the output of the dorsal motor nucleus. Similar influences
combine within the NTS itself, and the combined inhibitory influences on
the NTS and dorsal motor nucleus produce a general inhibitory effect.
[0219] The activation of inhibitory circuits in the periaqueductal gray,
raphe nucei, and locus coeruleus by the hypothalamus or NTS may also
cause circuits connecting each of these structures to modulate one
another. Thus, the periaqueductal gray communicates with the raphe nuclei
and with the locus coeruleus, and the locus coeruleus communicates with
the raphe nuclei, as shown in FIG. 12 [PUDOVKINA O L, Cremers T I,
Westerink B H. The interaction between the locus coeruleus and dorsal
raphe nucleus studied with dual-probe microdialysis. Eur J Pharmacol
7(2002); 445(1-2):37-42.; REICHLING D B, Basbaum A I. Collateralization
of periaqueductal gray neurons to forebrain or diencephalon and to the
medullary nucleus raphe magnus in the rat. Neuroscience 42(1,
1991):183-200; BEHBEHANI M M. The role of acetylcholine in the function
of the nucleus raphe magnus and in the interaction of this nucleus with
the periaqueductal gray. Brain Res 252(2, 1982):299-307]. The
periaqueductal gray, raphe nucei, and locus coeruleus are also shown in
FIG. 12 to project to many other sites within the brain.
[0220] The foregoing account of structures that are modulated by vagus
nerve stimulation is provided as background information needed to
understand another embodiment of the invention, in which vagus nerve
stimulation is used to modulate the activity of particular neural
networks known as resting state networks. A neural network in the brain
is accompanied by oscillations within the network. Low frequency
oscillations are likely associated with connectivity at the largest scale
of the network, while higher frequencies are exhibited by smaller
sub-networks within the larger network, which may be modulated by
activity in the slower oscillating larger network. The default network,
also called the default mode network (DMN), default state network, or
task-negative network, is one such network that is characterized by
coherent neuronal oscillations at a rate lower than 0.1 Hz. Other large
scale networks also have this slow-wave property, as described below
[BUCKNER R L, Andrews-Hanna J R, Schacter D L. The brain's default
network: anatomy, function, and relevance to disease. Ann N Y Acad Sci
1124(2008):1-38; PALVA J M, Palva S. Infra-slow fluctuations in
electrophysiological recordings, blood-oxygenation-level-dependent
signals, and psychophysical time series. Neuroimage 62(4,
2012):2201-2211; STEYN-ROSS M L, Steyn-Ross D A, Sleigh J W, Wilson M T.
A mechanism for ultra-slow oscillations in the cortical default network.
Bull Math Biol 73(2, 2011):398-416].
[0221] The default mode network corresponds to task-independent
introspection (e.g., daydreaming), or self-referential thought. When the
DMN is activated, the individual is ordinarily awake and alert, but the
DMN may also be active during the early stages of sleep and during
conscious sedation. During goal-oriented activity, the DMN is deactivated
and one or more of several other networks, so-called task-positive
networks (TPN), are activated. DMN activity is attenuated rather than
extinguished during the transition between states, and is observed,
albeit at lower levels, alongside task-specific activations. Strength of
the DMN deactivation appears to be inversely related to the extent to
which the task is demanding. Thus, DMN has been described as a
task-negative network, given the apparent antagonism between its
activation and task performance. The posterior cingulate cortex (PCC) and
adjacent precuneus and the medial prefrontal cortex (mPFC) are the two
most clearly delineated regions within the DMN [RAICHLE M E, Snyder A Z.
A default mode of brain function: a brief history of an evolving idea.
Neuroimage 37(4, 2007):1083-1090; BROYD S J, Demanuele C, Debener S,
Helps S K, James C J, Sonuga-Barke E J. Default-mode brain dysfunction in
mental disorders: a systematic review. Neurosci Biobehav Rev 33(3,
2009):279-96; BUCKNER R L, Andrews-Hanna J R, Schacter D L. The brain's
default network: anatomy, function, and relevance to disease. Ann N Y
Acad Sci 1124(2008):1-38; BUCKNER R L, Sepulcre J, Talukdar T, Krienen F
M, Liu H, Hedden T, Andrews-Hanna J R, Sperling R A, Johnson K A.
Cortical hubs revealed by intrinsic functional connectivity: mapping,
assessment of stability, and relation to Alzheimer's disease. J Neurosci
29(2009):1860-1873; GREICIUS M D, Krasnow B, Reiss A L, Menon V.
Functional connectivity in the resting brain: a network analysis of the
default mode hypothesis. Proc Natl Acad Sci USA 100(2003): 253-258].
[0222] The term low frequency resting state networks (LFRSN or simply RSN)
is used to describe both the task-positive and task-negative networks.
Using independent component analysis (ICA) and related methods to assess
coherence of fMRI Blood Oxygenation Level Dependent Imaging (BOLD)
signals in terms of temporal and spatial variation, as well as variations
between individuals, low frequency resting state networks in addition to
the DMN have been identified, corresponding to different tasks or states
of mind. They are related to their underlying anatomical connectivity and
replay at rest the patterns of functional activation evoked by the
behavioral tasks. That is to say, brain regions that are commonly
recruited during a task are anatomically connected and maintain in the
resting state (in the absence of any stimulation) a significant degree of
temporal coherence in their spontaneous activity, which is what allows
them to be identified at rest [SMITH S M, Fox P T, Miller K L, Glahn D C,
Fox P M, et al. Correspondence of the brain's functional architecture
during activation and rest. Proc Natl Acad Sci USA 106(2009):
13040-13045].
[0223] Frequently reported resting state networks (RSNs), in addition to
the default mode network, include the sensorimotor RSN, the executive
control RSN, up to three visual RSNs, two lateralized fronto-parietal
RSNs, the auditory RSN and the temporo-parietal RSN. However, different
investigators use different methods to identify the low frequency resting
state networks, so different numbers and somewhat different identities of
RSNs are reported by different investigators [COLE D M, Smith S M,
Beckmann C F. Advances and pitfalls in the analysis and interpretation of
resting-state FMRI data. Front Syst Neurosci 4(2010):8, pp. 1-15].
Examples of RSNs are described in publications cited by COLE and the
following: ROSAZZA C, Minati L. Resting-state brain networks: literature
review and clinical applications. Neurol Sci 32(5, 2011):773-85; ZHANG D,
Raichle M E. Disease and the brain's dark energy. Nat Rev Neurol 6(1,
2010):15-28; DAMOISEAUX, J. S., Rombouts, S. A. R. B., Barkhof, F.,
Scheltens, P., Stam, C. J., Smith, S. M., Beckmann, C. F. Consistent
resting-state networks across healthy subjects. Proc. Natl. Acad. Sci.
U.S.A. 103(2006): 13848-13853 FOX M D, Snyder A Z, Vincent J L, Corbetta
M, Van Essen D C, Raichle M E. The human brain is intrinsically organized
into dynamic, anticorrelated functional networks. Proc Natl Acad Sci USA
102(2005):9673-9678; LI R, Wu X, Chen K, Fleisher A S, Reiman E M, Yao L.
Alterations of Directional Connectivity among Resting-State Networks in
Alzheimer Disease. AJNR Am J Neuroradiol. 2012 Jul. 12. [Epub ahead of
print, pp. 1-6].
[0224] For example, the dorsal attention network (DAN) and ventral
attention network (VAN) are two networks responsible for attentional
processing. The VAN is involved in involuntary actions and exhibits
increased activity upon detection of salient targets, especially when
they appear in unexpected locations (bottom-up activity, e.g. when an
automobile driver unexpectedly senses a hazard or unexpected situation).
The DAN is involved in voluntary (top-down) orienting and increases
activity after presentation of cues indicating where, when, or to what
individuals should direct their attention [FOX M D, Corbetta M, Snyder A
Z, Vincent J L, Raichle M E. Spontaneous neuronal activity distinguishes
human dorsal and ventral attention systems. Proc Natl Acad Sci USA
103(2006):10046-10051; WEN X, Yao L, Liu Y, Ding M. Causal interactions
in attention networks predict behavioral performance. J Neurosci 32(4,
2012):1284-1292]. The DAN is bilaterally centered in the intraparietal
sulcus and the frontal eye field. The VAN is largely right lateralized in
the temporal-parietal junction and the ventral frontal cortex. According
to the present invention, it is generally desirable to activate DAN by
vagus nerve stimulation when biofeedback efforts are in progress.
[0225] The attention systems (e.g., VAN and DAN) have been investigated
long before their identification as resting state networks, and functions
attributed to the VAN have in the past been attributed to the locus
ceruleus/noradrenaline system [ASTON-JONES G, Cohen J D. An integrative
theory of locus coeruleus-norepinephrine function: adaptive gain and
optimal performance. Annu Rev Neurosci 28(2005):403-50; BOURET S, Sara S
J. Network reset: a simplified overarching theory of locus coeruleus
noradrenaline function. Trends Neurosci 28(11, 2005):574-82; SARA S J,
Bouret S. Orienting and Reorienting: The Locus Coeruleus Mediates
Cognition through Arousal. Neuron 76(1, 2012):130-41; BERRIDGE C W,
Waterhouse B D. The locus coeruleus-noradrenergic system: modulation of
behavioral state and state-dependent cognitive processes. Brain Res Brain
Res Rev 42(1, 2003):33-84].
[0226] The attention systems originally described by PETERSON and Posner
are more expansive than just the VAN and DAN system, with interacting
anatomical components corresponding to alerting, orienting, and executive
control [PETERSEN SE, Posner M I. The attention system of the human
brain: 20 years after. Annu Rev Neurosci 35(2012):73-89]. In that
description, DAN and VAN comprise significant portions of the orienting
system, and components largely involving locus ceruleus-norepinephrine
function comprise the alerting system. Other resting state networks are
involved with executive control [BECKMANN C F, DeLuca M, Devlin J T,
Smith S M. Investigations into resting-state connectivity using
independent component analysis. Philos Trans R Soc Lond B Biol Sci
360(1457, 2005):1001-1013].
[0227] MENON and colleagues describe the anterior insula as being at the
heart of the ventral attention system [ECKERT M A, Menon V, Walczak A,
Ahlstrom J, Denslow S, Horwitz A, Dubno J R. At the heart of the ventral
attention system: the right anterior insula. Hum Brain Mapp 30(8,
2009):2530-2541; MENON V, Uddin L Q. Saliency, switching, attention and
control: a network model of insula function. Brain Struct Funct 214(5-6,
2010):655-667]. However, SEELEY and colleagues used region-of-interest
and independent component analyses of resting-state fMRI data to
demonstrate the existence of an independent brain network comprised of
both the anterior insula and dorsal ACC, along with subcortical
structures including the amygdala, substantia nigra/ventral tegmental
area, and thalamus. This network is distinct from the other
well-characterized large-scale brain networks, e.g. the default mode
network [SEELEY W W, Menon V, Schatzberg A F, Keller J, Glover G H, Kenna
H, et al. Dissociable intrinsic connectivity networks for salience
processing and executive control. J Neurosci 2007; 27(9):2349-2356].
CAUDA and colleagues found that the human insula is functionally involved
in two distinct neural networks: i) the anterior pattern is related to
the ventral most anterior insula, and is connected to the rostral
anterior cingulate cortex, the middle and inferior frontal cortex, and
the temporoparietal cortex; ii) the posterior pattern is associated with
the dorsal posterior insula, and is connected to the dorsal-posterior
cingulate, sensorimotor, premotor, supplementary motor, temporal cortex,
and to some occipital areas [CAUDA F, D'Agata F, Sacco K, Duca S,
Geminiani G, Vercelli A. Functional connectivity of the insula in the
resting brain. Neuroimage 55(1, 2011):8-23; CAUDA F, Vercelli A. How many
clusters in the insular cortex? Cereb Cortex. 2012 Sep. 30. (Epub ahead
of print, pp. 1-2)]. TAYLOR and colleagues also report two such resting
networks [TAYLOR K S, Seminowicz D A, Davis K D. Two systems of resting
state connectivity between the insula and cingulate cortex. Hum Brain
Mapp 30(9, 2009):2731-2745]. DEEN and colleagues found three such resting
state networks [DEEN B, Pitskel N B, Pelphrey K A. Three systems of
insular functional connectivity identified with cluster analysis. Cereb
Cortex 21(7, 2011):1498-1506].
[0228] Before disclosing methods for modulating resting state networks
using vagal nerve stimulation, we first discuss how stimulation of the
vagus nerve can affect some of the relevant components of the brain, such
as the insula (see FIG. 12). These structures are involved in the
higher-level processing of sensory information. The sensory information
consists not only of hearing, vision, taste & smell, and touch that may
be used as biofeedback modalities, but also other sensory modalities such
as proprioception, nociception and other forms of interoception.
[0229] For purposes of illustration in FIG. 12, we use interoceptive
neural pathways leading to the insula [CRAIG AD. How do you feel--now?
The anterior insula and human awareness. Nat Rev Neurosci 10(1,
2009):59-70; BIELEFELDT K, Christianson J A, Davis B M. Basic and
clinical aspects of visceral sensation: transmission in the CNS.
Neurogastroenterol Motil 17(4, 2005):488-499; MAYER E A, Naliboff B D,
Craig A D. Neuroimaging of the brain-gut axis: from basic understanding
to treatment of functional GI disorders. Gastroenterology 131(6,
2006):1925-1942]. Anatomically, interoceptive sensations are
distinguished from surface touch (tactile) sensations by their
association with the spinothalamic projection that ascend in the
contralateral spinal cord, rather than with the dorsal column/medial
lemniscal system which ascends the ipsilateral spinal cord. However, both
contralateral and ipsilateral circuits are shown in the spinal cord in
FIG. 12 to indicate that the discussion applies more generally to sensory
processing, not just the interoception. In particular, it applies to also
to the circuits along which cutaneous sensations arising from electrical
stimulation are propagated [A. ANGEL. Processing of sensory information.
Progress in Neurobiology 9(1977):1-122; G. WEDDELL and S. Miller.
Cutaneous sensibility. Annual Review of Physiology 24(1962):199-222].
This is indicated in FIG. 12 as "Sensors within the skin", which are
electrically stimulated as "Cutaneous stimulation."
[0230] Interoceptive sensations arise from signals sent by parasympathetic
and sympathetic afferent nerves. The latter are considered to be the
primary culprit for pain and other unpleasant emotional feelings, but
parasympathetic afferents also contribute. Among afferents whose cell
bodies are found in the dorsal root ganglia, the ones having type B cell
bodies are most significant, which terminate in lamina I of the spinal
and trigeminal dorsal horns. Other afferent nerves that terminate in the
deep dorsal horn provide signals related to mechanoreceptive,
proprioceptive and nociceptive activity.
[0231] Lamina I neurons project to many locations. First, they project to
the sympathetic regions in the intermediomedial and intermediolateral
cell columns of the thoracolumbar cord, where the sympathetic
preganglionic cells of the autonomic nervous system originate (See FIG.
12). Second, in the medulla, lamina I neurons project to the A1
catecholaminergic cell groups of the ventrolateral medulla and then to
sites in the rostral ventrolateral medulla (RVLM) which is interconnected
with the sympathetic neurons that project to spinal levels. Only a
limited number of discrete regions within the supraspinal central nervous
system project to sympathetic preganglionic neurons in the
intermediolateral column (see FIG. 12). The most important of these
regions are the rostral ventral lateral medulla (RVLM), the rostral
ventromedial medulla (RVMM), the midline raphe, the paraventricular
nucleus (PVN) of the hypothalamus, the medullocervical caudal pressor
area (mCPA), and the A5 cell group of the pons. The first four of these
connections to the intermediolateral nucleus are shown in FIG. 12 [STRACK
A M, Sawyer W B, Hughes J H, Platt K B, Loewy A D. A general pattern of
CNS innervation of the sympathetic outflow demonstrated by transneuronal
pseudorabies viral infections. Brain Res. 491(1, 1989): 156-162].
[0232] The rostral ventral lateral medulla (RVLM) is the primary regulator
of the sympathetic nervous system, sending excitatory fibers
(glutamatergic) to the sympathetic preganglionic neurons located in the
intermediolateral nucleus of the spinal cord. Vagal afferents synapse in
the NTS, and their projections reach the RVLM via the caudal
ventrolateral medulla. However, resting sympathetic tone also comes from
sources above the pons, from hypothalamic nuclei, various hindbrain and
midbrain structures, as well as the forebrain and cerebellum, which
synapse in the RVLM. Only the hypothalamic projection to the RVLM is
shown in FIG. 12.
[0233] The RVLM shares its role as a primary regulator of the sympathetic
nervous system with the rostral ventromedial medulla (RVMM) and medullary
raphe. Differences in function between the RVLM versus RVMM/medullary
raphe have been elucidated for cardiovascular control, but are not well
characterized for control of other organs such as those of the gut.
Differential control of the RVLM by the hypothalamus may also occur via
circulating hormones such as vasopressin. The RVMM contains at least
three populations of nitric oxide synthase neurons that send axons to
innervate functionally similar sites in the NTS and nucleus ambiguus.
Circuits connecting the RVMM and RVLM may be secondary, via the NTS and
hypothalamus.
[0234] In the medulla, lamina I neurons also project another site, namely,
to the A2 cell group of the nucleus of the solitary tract, which also
receives direct parasympathetic (vagal and glossopharyngeal) afferent
input. As indicated above, the nucleus of the solitary tract projects to
many locations, including the parabrachial nucleus. In the pons and
mesencephalon, lamina I neurons project to the periaqueductal grey (PAG),
the main homeostatic brainstem motor site, and to the parabrachial
nucleus. Sympathetic and parasympathetic afferent activity is integrated
in the parabrachial nucleus. It in turn projects to the insular cortex by
way of the ventromedial thalamic nucleus (VMb, also known as VPMpc). A
direct projection from lamina I to the ventromedial nucleus (VMpo), and a
direct projection from the nucleus tractus solitarius to the VMb, provide
a rostrocaudally contiguous column that represents all contralateral
homeostatic afferent input. They project topographically to the
mid/posterior dorsal insula (See FIG. 12).
[0235] In humans, this cortical image is re-represented in the anterior
insula on the same side of the brain. The parasympathetic activity is
re-represented in the left (dominant) hemisphere, whereas the sympathetic
activity is re-represented in the right (non-dominant) hemisphere. These
re-representations provide the foundation for a subjective evaluation of
interoceptive state, which is forwarded to the orbitofrontal cortex (See
FIG. 12).
[0236] The right anterior insula is associated with subjective awareness
of homeostatic emotions (e.g., visceral and somatic pain, temperature,
sexual arousal, hunger, and thirst) as well as all emotions (e.g., anger,
fear, disgust, sadness, happiness, trust, love, empathy, social
exclusion). This region is intimately interconnected with the anterior
cingulate cortex (ACC). Unpleasant sensations are directly correlated
with ACC activation [KLIT H, Finnerup N B, Jensen T S. Central
post-stroke pain: clinical characteristics, pathophysiology, and
management. Lancet Neurol 8(9, 2009):857-868]. The anterior cingulate
cortex and insula are both strongly interconnected with the orbitofrontal
cortex, amygdala, hypothalamus, and brainstem homeostatic regions, of
which only a few connections are shown in FIG. 12.
[0237] Methods of the present invention comprise modulation of resting
state networks containing or interacting with the insula using vagus
nerve stimulation. A first method directly targets the front end of the
interoceptive pathways shown in FIG. 12 (nucleus tractus solitarius, area
postrema, and dorsal motor nucleus). The second method targets the distal
end of the interoceptive pathways (anterior insula and anterior cingulate
cortex).
[0238] According to the first method, electrical stimulation of A and B
fibers alone of a vagus nerve causes increased inhibitory
neurotransmitters in the brainstem, which in turn inhibits signals sent
to the parabrachial nucleus, VMb and VMpo. The stimulation uses special
devices and a special waveform (described above), which minimize effects
involving C fibers that might produce unwanted side-effects. The
electrical stimulation first affects the dorsal vagal complex, which is
the major termination site of vagal afferent nerve fibers. The dorsal
vagal complex consists of the area postrema (AP), the nucleus of the
solitary tract (NTS) and the dorsal motor nucleus of the vagus. The AP
projects to the NTS and dorsal motor nucleus of the vagus bilaterally. It
also projects bilaterally to the parabrachial nucleus and receives direct
afferent input from the vagus nerve. Thus, the area postrema is in a
unique position to receive and modulate ascending interoceptive
information and to influence autonomic outflow [PRICE C J, Hoyda T D,
Ferguson A V. The area postrema: a brain monitor and integrator of
systemic autonomic state. Neuroscientist 14(2, 2008):182-194].
[0239] Projections to and from the locus ceruleus are particularly
significant in the present invention because they are also used in the
second method that is described below. The vagus nerve transmits
information to the locus ceruleus via the nucleus tractus solitarius
(NTS), which has a direct projection to the dendritic region of the locus
ceruleus. Other afferents to, and efferents from, the locus ceruleus are
described by SARA et al, SAMUELS et al, and ASTON-JONES [SARA S J, Bouret
S. Orienting and Reorienting: The Locus Coeruleus Mediates Cognition
through Arousal. Neuron 76(1, 2012):130-41; SAMUELS E R, Szabadi E.
Functional neuroanatomy of the noradrenergic locus coeruleus: its roles
in the regulation of arousal and autonomic function part I: principles of
functional organisation. Curr Neuropharmacol 6(3):235-53; SAMUELS, E. R.,
and Szabadi, E. Functional neuroanatomy of the noradrenergic locus
coeruleus: its roles in the regulation of arousal and autonomic function
part II: physiological and pharmacological manipulations and pathological
alterations of locus coeruleus activity in humans. Curr. Neuropharmacol.
6(2008), 254-285; Gary ASTON-JONES. Norepinephrine. Chapter 4 (pp. 47-57)
in: Neuropsychopharmacology: The Fifth Generation of Progress (Kenneth L.
Davis, Dennis Charney, Joseph T. Coyle, Charles Nemeroff, eds.)
Philadelphia: Lippincott Williams & Wilkins, 2002].
[0240] In addition to the NTS, the locus ceruleus receives input from the
nucleus gigantocellularis and its neighboring nucleus
paragigantocellularis, the prepositus hypoglossal nucleus, the
paraventricular nucleus of the hypothalamus, Barrington's nucleus, the
central nucleus of the amygdala, and prefrontal areas of the cortex.
These same nuclei receive input from the NTS, such that stimulation of
the vagus nerve may modulate the locus ceruleus via the NTS and a
subsequent relay through these structures.
[0241] The locus ceruleus has widespread projections throughout the cortex
[SAMUELS E R, Szabadi E. Functional neuroanatomy of the noradrenergic
locus coeruleus: its roles in the regulation of arousal and autonomic
function part I: principles of functional organisation. Curr
Neuropharmacol 6 (3):235-53]. It also projects to subcortical regions,
notably the raphe nuclei, which release serotonin to the rest of the
brain. An increased dorsal raphe nucleus firing rate is thought to be
secondary to an initial increased locus ceruleus firing rate from vagus
nerve stimulation [Adrienne E. DORR and Guy Debonnelv. Effect of vagus
nerve stimulation on serotonergic and noradrenergic transmission. J
Pharmacol Exp Ther 318(2, 2006):890-898; MANTA S, Dong J, Debonnel G,
Blier P. Enhancement of the function of rat serotonin and norepinephrine
neurons by sustained vagus nerve stimulation. J Psychiatry Neurosci 34(4,
2009):272-80]. The locus ceruleus also has projections to autonomic
nuclei, including the dorsal motor nucleus of the vagus, as shown in FIG.
1A [FUKUDA, A., Minami, T., Nabekura, J., Oomura, Y. The effects of
noradrenaline on neurones in the rat dorsal motor nucleus of the vagus,
in vitro. J. Physiol., 393 (1987): 213-231; MARTINEZ-PENA y Valenzuela,
I., Rogers, R. C., Hermann, G. E., Travagli, R. A. (2004) Norepinephrine
effects on identified neurons of the rat dorsal motor nucleus of the
vagus. Am. J. Physiol. Gas-trointest. Liver Physiol., 286, G333-G339;
TERHORST, G. J., Toes, G. J., Van Willigen, J. D. Locus coeruleus
projections to the dorsal motor vagus nucleus in the rat. Neuroscience,
45(1991): 153-160].
[0242] The above-mentioned circuits shown can be represented in terms of
functional resting state networks that may also contain various
components that are shown in FIG. 12. A simplified representation of
those networks is shown in FIG. 13. For purposes of discussion, we adopt
the set of resting state networks identified by L I et al, with the
understanding that according to the above-cited publications, a more or
less detailed set could also be adopted [LI R, Wu X, Chen K, Fleisher A
S, Reiman E M, Yao L. Alterations of Directional Connectivity among
Resting-State Networks in Alzheimer Disease. AJNR Am J Neuroradiol. 2012
Jul. 12. [Epub ahead of print, pp. 1-6]. A similar set of resting state
networks is described by DING et al [DING J R, Liao W, Zhang Z, Mantini
D, Xu Q, Wu G R, Lu G, Chen H. Topological fractionation of resting-state
networks. PLoS One 6(10, 2011):e26596, pp. 1-9]. FIG. 13 also shows
connections between the networks, with the larger arrows indicating
stronger connections. Solid and dashed arrows are, respectively, for
positive and negative connections.
[0243] As described above, the dorsal attention network (DAN) and ventral
attention network (VAN) are two networks responsible for attentional
processing. The VAN is involved in involuntary actions and exhibits
increased activity upon detection of salient targets, especially when
they appear in unexpected locations (bottom-up activity, e.g. when an
automobile driver unexpectedly senses a hazard). The DAN is involved in
voluntary (top-down) orienting and increases activity after presentation
of cues indicating where, when, or to what individuals should direct
their attention [FOX M D, Corbetta M, Snyder A Z, Vincent J L, Raichle M
E. Spontaneous neuronal activity distinguishes human dorsal and ventral
attention systems. Proc Natl Acad Sci USA 103(2006):10046-10051; WEN X,
Yao L, Liu Y, Ding M. Causal interactions in attention networks predict
behavioral performance. J Neurosci 32(4, 2012):1284-1292]. The DAN is
bilaterally centered in the intraparietal sulcus and the frontal eye
field. The VAN is largely right lateralized in the temporal-parietal
junction and the ventral frontal cortex.
[0244] The sensory-motor network (SMN) is the network covering the
somatosensory, premotor, and supplementary motor cortices. Cutaneous
stimulation would preferentially activate the SMN, so the vagus nerve
stimulation may be directed to affect the SMN to enhance the cutaneous
signals. The lateral visual network (LVN) and medial visual network (MVN)
are two networks for visual processing and are respectively located in
the lateral and medial parts of the visual cortex. The auditory network
(AN) is responsible for auditory processing and is located in the
bilateral superior temporal gyrus and in the primary and secondary
auditory cortices. The LVN, MVN, AN, and SMN are four networks related to
sensory processing, and the DMN, SRN, DAN, and VAN are associated with
higher cognitive function.
[0245] The present invention modulates the activity of these resting state
networks via the locus ceruleus by electrically stimulating the vagus
nerve, as indicated in FIG. 13. Stimulation of a network by that route
may activate or deactivate a resting state network, depending on the
detailed configuration of adrenergic receptor subtypes within the network
and their roles in enhancing or depressing neural activity within the
network, as well as subsequent network-to-network interactions.
[0246] According to the invention, one key to preferential stimulation of
a particular resting state network, such as those involving the insula,
is to use a vagus nerve stimulation signal that entrains to the signature
EEG pattern of that network (see below and MANTINI D, Perrucci M G, Del
Gratta C, Romani G L, Corbetta M. Electrophysiological signatures of
resting state networks in the human brain. Proc Natl Acad Sci USA 104(32,
2007):13170-13175). By this EEG entrainment method, it may be possible to
preferentially activate, attenuate or deactivate particular networks,
such as DAN or VAN. Activation of another network such as the SMN, VAN or
DMN may also produce the same effect, via network-to-network
interactions. Although the locus ceruleus is presumed to project to all
of the resting networks, it is thought to project most strongly to the
ventral attention network (VAN) [CORBETTA M, Patel G, Shulman G L. The
reorienting system of the human brain: from environment to theory of
mind. Neuron 58(3, 2008):306-24; MANTINI D, Corbetta M, Perrucci M G,
Romani G L, Del Gratta C. Large-scale brain networks account for
sustained and transient activity during target detection. Neuroimage
44(1, 2009):265-274]. Thus, deactivation of a particular network may also
be attempted by activating another resting state network, because the
brain switches between them.
[0247] Stimulation waveforms may be constructed by superimposing or mixing
the burst waveform shown in FIGS. 11B and 11C, in which each component of
the mixture may have a different period T, effectively mixing different
burst-per-second waveforms. The relative amplitude of each component of
the mixture may be chosen to have a weight according to correlations in
different bands in an EEG for a particular resting state network. Thus,
MANTINI et al performed simultaneous fMRI and EEG measurements and found
that each resting state network has a particular EEG signature [see FIG.
3 in: MANTINI D, Perrucci M G, Del Gratta C, Romani G L, Corbetta M.
Electrophysiological signatures of resting state networks in the human
brain. Proc Natl Acad Sci USA 104(32, 2007):13170-13175]. They reported
relative correlations in each of the following bands, for each resting
state network that was measured: delta (1-4 Hz), theta (4-8 Hz), alpha
(8-13 Hz), beta (13-30 Hz), and gamma (30-50 Hz) rhythms. For
recently-identified resting state networks, measurement of the
corresponding signature EEG networks will have to be performed.
[0248] According to the present embodiment of the invention, multiple
signals shown in FIGS. 11B and 11C are constructed, with periods T that
correspond to a location near the midpoint of each of the EEG bands
(e.g., using the MINATI data, T equals approximately 0.4 sec, 0.1667 sec,
0.095 sec, 0.0465 sec, and 0.025 sec, respectively). A more comprehensive
mixture could also be made by mixing more than one signal for each band.
These signals are then mixed, with relative amplitudes corresponding to
the weights measured for any particular resting state network, and the
mixture is used to stimulate the vagus nerve of the patient. Phases
between the mixed signals are adjusted to optimize the fMRI signal for
the resting state network that is being stimulated, thereby producing
entrainment with the resting state network. Stimulation of a network may
activate or deactivate a network, depending on the detailed configuration
of adrenergic receptors within the network and their roles in enhancing
or depressing neural activity within the network, as well as subsequent
network-to-network interactions. It is understood that variations of this
method may be used when different combined fMRI-EEG procedures are
employed and where the same resting state may have different EEG
signatures, depending on the circumstances [WU C W, Gu H, Lu H, Stein E
A, Chen J H, Yang Y. Frequency specificity of functional connectivity in
brain networks. Neuroimage 42(3, 2008):1047-1055; LAUFS H. Endogenous
brain oscillations and related networks detected by surface EEG-combined
fMRI. Hum Brain Mapp 29(7, 2008):762-769; MUSSO F, Brinkmeyer J,
Mobascher A, Warbrick T, Winterer G. Spontaneous brain activity and EEG
microstates. A novel EEG/fMRI analysis approach to explore resting-state
networks. Neuroimage 52(4, 2010):1149-1161; ESPOSITO F, Aragri A, Piccoli
T, Tedeschi G, Goebel R, Di Salle F. Distributed analysis of simultaneous
EEG-fMRI time-series: modeling and interpretation issues. Magn Reson
Imaging 27(8, 2009):1120-1130; FREYER F, Becker R, Anami K, Curio G,
Villringer A, Ritter P. Ultrahigh-frequency EEG during fMRI: pushing the
limits of imaging-artifact correction. Neuroimage 48(1, 2009):94-108].
Once the network is entrained, one may also attempt to change the
signature EEG pattern of a network, by slowly changing the frequency
content of the stimulation & EEG pattern of the network to which the
stimulator is initially entrained. An objective in this case would be to
modify the frequency content of the resting state signature EEG.
[0249] We conclude this section by noting that very few publications
discuss the relevance of resting state networks to biofeedback, and none
of them deal also with vagus nerve stimulation [R. Cameron CRADDOCK,
Jonathan Lisinski, Pearl Chiu, Helen Mayberg, Stephen LaConte. Real-time
tracking and biofeedback of the default mode network. Poster No. 648,
Jun. 11, 2012. In: Proc. 18th OHBM Meeting., Jun. 10-14, 2012. Beijing
China. Organization for Human Brain Mapping. 5841 Cedar Lake Road, Suite
204 Minneapolis, Minn. 55416, pp. 1-3]. As noted above, portions of fMRI
images have been used for region-of-interest fMRI neurobeedback, but they
are not concerned specifically with whole resting state networks.
Otherwise, fMRI imaging has been used only to see what portions of the
brain are activated during biofeedback [CRITCHLEY H D, Melmed R N,
Featherstone E, Mathias C J, Dolan R J. Brain activity during biofeedback
relaxation: a functional neuroimaging investigation. Brain 124(5,
2001):1003-1012].
[0250] Biofeedback and Automatic Stimulation Protocols
[0251] Methods for treating and training a patient according to the
present invention comprise stimulating the vagus nerve as indicated in
FIGS. 1C, 7 and 8, using the electrical stimulation devices and
stimulation waveforms that are disclosed here, such as those in FIGS. 3
and 11. Stimulation may be performed on the left or right vagus nerve, or
on both of them simultaneously or alternately. The position and angular
orientation of the device are adjusted at the preferred location on the
neck, above the vagus nerve, until the patient perceives stimulation when
current is passed through the stimulator electrodes. The applied current
is increased gradually, first to a level wherein the patient feels
sensation from the stimulation. The power is then increased, but is set
to a level that is less than one at which the patient first indicates any
discomfort. The correctness of the location of the stimulator on the
patient's neck may be verified by any of the methods disclosed in the
co-pending, commonly assigned application U.S. Ser. No. 13/872,116,
entitled DEVICES AND METHODS FOR MONITORING NON-INVASIVE VAGUS NERVE
STIMULATION, to SIMON et al., which is incorporated by reference].
Straps, harnesses, or frames may then be used to maintain the stimulator
in position (see FIG. 8).
[0252] Physiological sensors will be attached to the patient, and the
corresponding physiological measurements will then be made continuously,
as described in the section above entitled "Use of biofeedback and
automatic control theory methods to treat and train patients."
Ordinarily, one of those physiological signals will be used to construct
a biofeedback signal that is applied electrically to the skin of the
patient's neck. The appropriate range of that electrocutaneous
biofeedback signal will then be determined as described in the section
above entitled "Selection of the electrical stimulation waveform," with
the vagus nerve stimulation reduced to an amplitude that is not
sufficient to materially stimulate the vagus nerve. Other biofeedback
signal modalities could be used too, such as an audio or visual
biofeedback signal, but they are not used in the basic invention.
[0253] At this point, the patient will attempt to use biofeedback to
modify the relevant physiological signal, or will be trained to do so.
For example, the physiological signal could be an electrodermal sensor
for measuring galvanic skin response, a thermometer for measuring finger
temperature and the associated blood flow, or an EEG-derived signal.
Strategies for voluntarily modulating the biofeedback signal include
deliberately entering a particular emotional state or relaxing muscles.
The invention is intended to work with any of the biofeedback signals
that have been described in literature that is cited herein, and the
intended biomedical applications of such published biofeedback methods
apply as well to the present invention.
[0254] According to one view, individuals who learn to perform biofeedback
do so through a type of neural natural selection, in which pre-existing,
randomly-activated efferent neural circuit paths are consciously
selected, and the pool of possible circuit paths is measured by the
person-to-person lability of the corresponding physiological variable.
According to this view, an individual with little lability will have few
circuit paths from which to select, and will therefore be disadvantaged
in terms of his or her potential to learn biofeedback skills. That is to
say, by measuring the natural, unprovoked physiological variability in
the physiological signal that is used for biofeedback, i.e., the
magnitude of apparent "noise" in the signal about a baseline, one might
be able to infer the likelihood that the individual will be able to learn
to perform biofeedback [R. Sergio GUGLIELMI and Alan H. Roberts.
Volitional vasomotor lability and vasomotor control. Biological
Psychology 39(1994):29-44].
[0255] This view is sometimes referred to as an efferent or so-called
"feedforward" mechanism of biofeedback learning. Note that use of the
term "feedforward" in this sense refers to the efferent direction and has
nothing to do with the above-mentioned use of the term "feedforward" in
engineering control theory. According to the present invention, if the
vagus nerve is even stimulated with a sequence of randomly selected
stimulation parameters so as to indirectly and artificially increase the
lability of the physiological signal, this alone may increase the
likelihood that the patient may learn to perform biofeedback [Thomas G.
DUNN, Scott E. Gillig, Sharon E. Ponsor, Nolan Weil, and Sharon Williams
Utz. The learning process in biofeedback: is it feedforward or feedback?
Biofeedback and Self-Regulation 11(2, 1986):143-156; Sharon Williams UTZ.
The effect of instructions on cognitive strategies and performance in
biofeedback. Journal of Behavioral Medicine 17(3, 1994):291-308; J. M.
LACROIX. The acquisition of autonomic control through biofeedback: the
case against an afferent process and a two-process alternative.
Psychophysiology 18(5, 1981):573-587].
[0256] An alternate, and not mutually exclusive, view of biofeedback
learning is that the acquisition of voluntary visceral control is
dependent upon the ability to perceive or discriminate changes in
visceral function. According to this view, biofeedback enhances
discrimination of interoceptive events by providing additional
exteroceptive cues. Thus, the individual must learn to discriminate
interoceptive cues related to the target response and to develop skills
so as to attain control of the response, including possibly the
development of new sensory abilities during the training process. This
view of biofeedback learning is sometimes known as an "afferent"
mechanism, to distinguish it from the "efferent" mechanism described in
the previous paragraph.
[0257] The present invention provides another mechanism whereby such
discrimination can occur. Instead of, or in addition to, providing the
additional exeroceptive cues, the present invention is novel in that it
provides additional interoceptive clues. These cues are indicated in FIG.
1C as "interoceptive sensation." The figure refers not to naturally
occurring interoceptive signals, but instead to interoceptive signals
that are produced artificially as a result of the vagus nerve
stimulation. They correspond to the stimulation of afferent vagus nerve
fibers that convey a sense of their excitation to regions of the brain
that could result in the conscious but artificial awareness of the
viscera, particularly the anterior insula (see FIG. 12) [CRITCHLEY H D,
Wiens S, Rotshtein P, Ohman A, Dolan R J. Neural systems supporting
interoceptive awareness. Nat Neurosci 7(2, 2004):189-195; CRAIG, A. D.
How do you feel? Introception: the sense of the physiological condition
of the body. Nat. Rev. Neurosci 3(2002):655-666; CRAIG AD. How do you
feel--now? The anterior insula and human awareness. Nat Rev Neurosci
10(1, 2009):59-70]. In one embodiment, the magnitude of stimulation of
those afferent fibers is made to increase or decrease according to the
corresponding level of the physiological signal that is being sensed. One
may regard that method as a type of augmented biofeedback that involves
interoceptive sensation, rather than exteroceptive sensation. This
stimulation of afferent vagal nerve fibers is also intended to simulate
the adaptation of interoceptors that may be required for the direct,
voluntary control of the viscera [Barry R. DWORKIN. Learning and
Physiological Regulation. Chicago: University of Chicago Press, 1993,
Chapter 8, pp. 162-185].
[0258] After determining whether and to what extent the patient is able to
consciously control the biofeedback signal, biofeedback will be suspended
and the parameters suitable for vagus nerve stimulation will then be
determined. Ordinarily, the amplitude of the stimulation signal is set to
the maximum that is comfortable for the patient, and then the other
stimulation parameters are adjusted. In general, the stimulator signal
may have a frequency and other parameters that are selected to produce a
therapeutic result in the patient, i.e., stimulation parameters for each
patient are adjusted on an individualized basis, in order to produce an
effect that is relevant to the condition that is being treated. The
parameter values may be selected in such a way as to activate or suppress
particular resting state networks of the brain that are relevant to the
patient's condition, as described in the section above entitled
"Selection of stimulation parameters to activate or suppress selected
resting state networks of the brain." Preliminary control theory
procedures, including tuning and the training of a support vector
machine, may also be performed in order to allow the system to vary its
stimulation parameters in response to fluctuating environmental and
sensed physiological signals, as described in the section "Use of
biofeedback and automatic control theory methods to treat and train
patients."
[0259] A typical stimulation waveform was shown in FIGS. 11B and 11C. As
seen there, individual sinusoidal pulses have a period of tau, and a
burst consists of N such pulses. This is followed by a period with no
signal (the inter-burst period). The pattern of a burst followed by
silent inter-burst period repeats itself with a period of T. For example,
the sinusoidal period tau may be 200 microseconds; the number of pulses
per burst may be N=5; and the whole pattern of burst followed by silent
inter-burst period may have a period of T=40000 microseconds, which is
comparable to 25 Hz stimulation. More generally, there may be 1 to 20
pulses per burst, preferably five pulses. Each pulse within a burst has a
duration of 1 to 1000 microseconds (i.e., about 1 to 10 KHz), preferably
200 microseconds (about 5 KHz). A burst followed by a silent inter-burst
interval repeats at 1 to 5000 bursts per second (bps), preferably at 5-50
bps, and even more preferably 10-25 bps stimulation (10-25 Hz). The
preferred shape of each pulse is a full sinusoidal wave, although
triangular or other shapes may be used as well.
[0260] Such a signal may be constructed by circuits within the stimulator
housing (30 in FIG. 3), or it may be transmitted to the housing using
radio transmission from the base station or any of the other components
of the control unit (see FIG. 6). Compression of the signal is also
possible, by transmitting only the signal parameters tau, N, T, Emax,
etc., but in that case, the stimulator housing's control electronics
would then have to construct the waveform from the transmitted
parameters.
[0261] After the cutaneous and deep nerve stimulation waveform parameters
have been preliminarily selected, and it has been determined that the
patient can perform biofeedback, stimulation sessions can be initiated in
which the biofeedback and vagus nerve stimulation are performed
simultaneously. The duration of a stimulation session depends on the
physiological condition that is being treated, and success of the
stimulation may be judged in terms of whether the sensed physiological
signal is adjusted by the stimulation to be within a clinically desirable
range. Alternatively, other indices of clinical success may be made,
depending on the condition that is being treated.
[0262] The three mechanisms shown in FIG. 1C (biofeedback, artificial
interoceptive sensation, and direct stimulation via the vagus nerve to
effect automatic control) will collectively modulate the physiological
system, interacting with one another to determine the value of the sensed
physiological signal. Part of the interaction is determined by the manner
in which the nerve stimulator/biofeedback device/physiological controller
is programmed. For example, direct stimulation of the physiological
system via the vagus nerve may be programmed to follow and amplify
changes that occur as a result of biofeedback. An embodiment of that
example would occur when the individual uses galvanic skin response
biofeedback alone to consciously reduce sympathetic tone through muscular
and emotional modulation, whereupon the device senses that reduction
through its programming and then amplifies the effect by increasing
parasympathetic tone after a brief time delay, by directly stimulating
vagal parasympathetic efferent nerve fibers.
[0263] A similar example is when the patient is using heart rate
variability biofeedback alone to increase the amplitude of his or her
respiratory sinus arrhythmia, whereupon the device senses that increase
and then amplifies the effect by increasing parasympathetic tone after a
brief time delay, by directly stimulating vagal parasympathetic efferent
nerve fibers. In those examples, it is clear what the biofeedback effect
is initially, and the vagus stimulation is only applied thereafter to
amplify or enhance it. In other embodiments that are disclosed in the
section above, entitled "Use of biofeedback and automatic control theory
methods to treat and train patients," both biofeedback and vagus nerve
stimulation are performed simultaneously, and mathematical modeling is
used to infer the effects that are due to the biofeedback, thereby
allowing the device to infer the intentions of the individual and apply
the vagus nerve stimulation accordingly.
[0264] For the subset of individuals who are unable to control their
physiological signals adequately using biofeedback, even after multiple
training attempts, and even with amplification of the biofeedback effects
using vagus nerve stimulation as described above, the device shown in
FIG. 1C may also be programmed to use vagus nerve stimulation alone to
perform the control automatically.
[0265] We conclude this section by giving a few examples of the use of the
present invention. The first example involves individuals who are
paralyzed from the neck down, who suffer severe hypotension when they are
moved from a horizontal to an upright position. Despite their muscular
paralysis, some of them can learn to increase their blood pressure when
needed as a countermeasure, by deliberately getting angry. However, other
such individuals could benefit from an embodiment of the present device,
wherein the sensed physiological signals are the EEG and blood pressure,
and the applied vagus nerve stimulation is one that is designed to
increase blood pressure. In this embodiment, the EEG is used as a
brain-computer interface, possibly with visual or auditory biofeedback,
which uses the computer to control operation of the vagus nerve
stimulator [HADLER S, Agorastos D, Veit R, Hammer E M, Lee S, Varkuti B,
Bogdan M, Rosenstiel W, Birbaumer N, Kubler A. Neural mechanisms of
brain-computer interface control. Neuroimage 55(4, 2011):1779-1790]. Care
must be taken in selecting the parameters of vagus nerve stimulation,
which occurs after it is initiated by the patient through deliberate EEG
signaling to the computer, because some stimulation parameters will
increase blood pressure, but others could actually decrease the blood
pressure [Robert G. FELDMAN. A systematic study of parameters of afferent
vagal stimulation in the anesthetized dog: Blood pressure reflexes. Acta
Neurovegetativa 1962, Volume 25(1, 1962):134-143; BEN-ISHAY D, Grupp I L,
Grupp G. The "humoral" component of the pressor response to central vagal
stimulation and the identification of the "humor" as norepinephrine. J
Pharmacol Exp Ther 154(3, 1966):524-530; Dennis T. T. PLACHTA, Mortimer
Gierthmuehlen, Oscar Cota, Fabian Boeser and Thomas Stieglitz. BaroLoop:
Using a multichannel cuff electrode and selective stimulation to reduce
blood pressure. Proc. 35th Annual International Conference of the IEEE
EMBS, Osaka, Japan, 3-7 Jul., 2013, pp. 755-758].
[0266] A second example involve the use of heart rate variability (HRV)
biofeedback to increase the amplitude of respiratory sinus arrhythmia
(RSA). The training is based on the existence of two prominent peaks in
the heart rate Fourier spectrum, one of which is related to respiratory
sinus arrhythmia, and the other of which is related to the baroreflex and
Mayer waves. As ordinarily practiced in HRV biofeedback, the individual's
breathing rate is deliberately reduced so as to move the respiratory
sinus arrhythmia peak close to the Mayer wave peak, in order to exploit a
resonance that causes the magnitude of the respiratory sinus arrhythmia
peak to increase [LEHRER P M, Vaschillo E, Vaschillo B. Resonant
frequency biofeedback training to increase cardiac variability: rationale
and manual for training. Appl Psychophysiol Biofeedback 25(3,
2000):177-191]. Greater flexibility is provided by an embodiment of the
present invention, in which a visual biofeedback representation of the
heart rate Fourier spectrum is provided to the patient, and the vagus
nerve is stimulated. As the patient reduces his or her breathing rate,
the device senses that the patient is attempting to move the location of
the respiratory sinus arrhythmia peak and begins to stimulate the vagus
nerve. As noted in the previous paragraph, depending on the parameters of
vagus nerve stimulation, the blood pressure may be caused to increase or
decrease, and in this embodiment of the invention, the increase and
decrease is caused to occur periodically with a frequency that is
generally different than the naturally occurring Mayer wave frequency.
The stimulation may also be performed during particular phases of the
respiratory cycle in order to give the method even more flexibility.
Resonances therefore occur through the interaction not only between the
RSA peak and Mayer wave peak, but also between those peaks and the
artificially produced blood pressure wave that is generated through vagus
nerve stimulation. The interaction is apparent to the patient for
purposes of biofeedback by viewing the current HRV spectrum, and the
patient may then find a breathing rate that not only is more comfortable
than the slow rate used for ordinary HRV biofeedback, but that also
produces an enhanced RSA amplitude relative to the one that is possible
using ordinary HRV biofeedback.
[0267] As a third example, consider use of an embodiment of the invention
to treat patients who suffer from migraine headaches. Electromyographic
(EMG) biofeedback is said to promote a general sense of relaxation within
the entire body, wherein the patient hears a tone through headphones,
with the audio frequency proportional to the EMG activity in the muscle
being monitored (most often the frontalis and/or trapezius muscle).
Muscle metabolism and the relative ischemia that results from compression
of blood vessels by the contracting muscle generate metabolic products,
particularly adenosine, which then activate chemo-sensitive afferent
nerves. These chemoreceptors constitute the afferent limb of a reflex
that results in sympathetic activation [COSTA F, Biaggioni I. Role of
adenosine in the sympathetic activation produced by isometric exercise in
humans. J Clin Invest.93(1994):1654-1660]. Such muscle contraction may
occur involuntarily in migraine patients, analogous to grimacing that
accompanies pain or its anticipation, resulting in sympathetic activation
and even more pain. Relaxation of muscles using EMG biofeedback methods
may therefore counteract such a migraine-promoting positive feedback loop
[William J. MULLALLY, Kathryn Hall M S, and Richard Goldstein. Efficacy
of Biofeedback in the Treatment of Migraine and Tension Type Headaches.
Pain Physician 12(2009):1005-1011; Yvonne NESTORIUC, Alexandra Martin,
Winfried Rief, Frank Andrasik. Biofeedback Treatment for Headache
Disorders: A Comprehensive Efficacy Review. Appl Psychophysiol
Biofeedback 33(2008):125-140].
[0268] The present invention may be used to amplify such
biofeedback-induced effects by first detecting the patient's attempted
muscular relaxation and the associated reduction in sympathetic tone, and
by then stimulating the vagus nerve to increase parasympathetic tone.
However, this is not the only positive feedback loop that one may hope to
prevent or break in migraine patients, and it may be desirable to
actually decrease parasympathetic tone in certain neuronal circuits. In
particular, a migraine-related pathway involves pre- and postganglionic
parasympathetic neurons in the superior salivatory nucleus (SSN) and
sphenopalatine ganglion (SPG), respectively. The SSN stimulates the
release of acetylcholine, vasopressin intestinal peptide, and nitric
oxide from meningeal terminals of SPG neurons, resulting directly or
indirectly in the migraine-related cascade of events that include the
dilation of intracranial blood vessels, plasma protein extravasation, and
local release of inflammatory molecules that activate adjacent terminals
of meningeal nociceptors. The SSN receives extensive input from more than
fifty brain areas, many of which may be modulated by the locus ceruleus.
[0269] When the locus ceruleus is activated through vagus nerve
stimulation, it will respond by increasing norepinephrine secretion,
which in turn will alter cognitive function through the prefrontal
cortex, increase motivation through nucleus accumbens, activate the
hypothalamic-pituitary-adrenal axis, and increase the sympathetic
discharge/inhibit parasympathetic tone through the brainstem. Such
inhibition of parasympathetic tone will specifically inhibit the
parasympathetic pathway via the superior salivatory nucleus, thereby
blocking the positive feedback loop that contributes to the maintenance
of migraine pain [Commonly assigned, co-pending patent application
US20110276107, entitled Electrical and magnetic stimulators used to treat
migraine/sinus headache, rhinitis, sinusitis, rhinosinusitis, and
comorbid disorders, to SIMON et al, which is hereby incorporated by
reference].
[0270] Tibial Nerve Stimulation in Conjunction with Biofeedback for
Urinary Incontinence
[0271] As a final example, we disclose another use of the device shown in
FIG. 1C, to illustrate stimulation of a nerve other than the vagus nerve.
In the example, the tibial nerve in the vicinity of the patient's ankle
is stimulated, for treatment of urinary incontinence. Urinary
incontinence is a common problem, and physical therapies, particularly
pelvic floor muscle exercise (commonly known as Kegel exercise), are the
mainstay of their conservative management. Depending on the type of
urinary incontinence, patients are taught to contract the pelvic floor
muscles, relax the detrusor and the abdominal muscles, and/or contract
the sphincters. Pelvic floor muscle exercise is particularly beneficial
in the treatment of urinary stress incontinence in females [PRICE N,
Dawood R, Jackson S R. Pelvic floor exercise for urinary incontinence: a
systematic literature review. Maturitas 67(4, 2010):309-315].
[0272] Kegel exercises are often used in conjunction with biofeedback
training that involves electromyographic measurement of pelvic floor
muscle activity, which provides awareness of the physiological action of
the muscles using visual, tactile or auditory biofeedback signals. Such
biofeedback training is commonly known as biofeedback-assisted pelvic
muscle training (BFB). It helps the patient identify their pelvic
muscles, measure the strength of pelvic muscles and provided a
quantitative measure of the effectiveness of the Kegel exercises. The
rationale for using biofeedback is as follows. Weak muscles give off only
weak propriceptive sensations, and the biofeedback is intended to
supplement those sensations. When the pelvic floor muscles are weak,
there is also a tendency to unintentionally substitute abdominal and
gluteal contractions, making the Kegel exercises useless, but which the
biofeedback makes apparent. Furthermore, the biofeedback signals give the
patient the satisfaction of actually witnessing
electromyographically-sensed improvements to the muscle. Often, the
design of the biofeedback probe calls for its placement into either the
vagina or anal canal. Another EMG electrode may be placed on the abdomen
to determine use of accessory or gluteus muscles and hip adductors
[GLAZER H I, Laine C D. Pelvic floor muscle biofeedback in the treatment
of urinary incontinence: a literature review. Appl Psychophysiol
Biofeedback 31(3, 2006):187-201].
[0273] Biofeedback for urinary incontinence is generally regarded as safe
and potentially effective and is considered medically necessary by most
medical insurers. However, there is a significant subpopulation of
individuals for whom biofeedback-assisted pelvic muscle training is only
marginally effective [RESNICK N M, Perera S, Tadic S, Organist L, Riley M
A, Schaefer W, Griffiths D. What predicts and what mediates the response
of urge urinary incontinence to biofeedback? Neurourol Urodyn 32(5,
2013):408-415]. For such individuals, stimulation of the tibial nerve
near the ankle for typically 5 minutes may help inhibit bladder
contractions, and that inhibition persists for up to an hour after
stimulation ceases. The posterior tibial nerve that is stimulated
contains mixed sensory motor nerve fibers that originate from the same
spinal segments as the innervations to the bladder and pelvic floor.
Mechanisms of action of the tibial nerve stimulation in regards to
urinary incontinence are disclosed in the co-pending, commonly assigned
patent application U.S. Ser. No. 13/279,437 (publication US20120101326),
entitled NON-INVASIVE ELECTRICAL AND MAGNETIC NERVE STIMULATORS USED TO
TREAT OVERACTIVE BLADDER AND URINARY INCONTINENCE, to SIMON et al, which
is hereby incorporated by reference.
[0274] FIG. 14 illustrates use of the device shown in FIG. 3 to stimulate
the posterior tibial nerve, in which the stimulator device 30 is applied
to a target location above the patient's ankle. The method stimulates the
posterior tibial nerve 60, which runs down the lower leg (crus) and into
the foot as indicated in the figure. To perform the stimulation, the
stimulator is first positioned approximately 3 finger breadths cephalad
from the protruding medial malleolus 61 and about 1 finger breadth
posterior from the edge of the tibia 62. In the present invention, the
stimulation may be performed in conjunction with the deliberate
contraction or relaxation of pelvic floor muscles, which may be sensed
using the same sensors that are used in connection with
biofeedback-assisted pelvic muscle training. Thus, the sensors are used
not only to generate a visual or audio biofeedback signal, but they are
also used to initiate and control stimulation of the tibial nerve
stimulator, as shown in FIG. 1C with "Vagus" replaced with "Tibial." The
"Cutaneous and Other Senses" in FIG. 1C are then concerned primarily with
the "Other Senses", namely, auditory and visual senses that sense a
conventional biofeedback signal. Similarly to the case of vagus nerve
stimulation that is used in conjunction with biofeedback, the tibial
nerve stimulation may be programmed to amplify the deliberate and
voluntary efforts of the patient, as evidenced by alteration of the
sensed electromyographic signals.
[0275] Although stimulation of the tibial nerve is a preferred embodiment
for combined biofeedback and automatic control of muscles involved in
urinary incontinence, it is understood that other nerves may be
stimulated as well. In other embodiments, nerves that may be stimulated
noninvasively comprise the pudendal nerve, sciatic nerve, superior
gluteal nerve, lumbo-sacral trunk, inferior gluteal nerve, common fibular
nerve, posterior femoral cutaneous nerve, obturator nerve, common
peroneal nerve, plantar nerve, sacral nerves S1, S2, S3, or S4, or nerves
of the S1, S2, S3, or S4 dermatome, and sacral anterior root nerves. The
invention also contemplates sites of stimulation that comprise
innervations of the urethral sphincter and pelvic floor muscles, the
suprapubic area, rectum or anus, vagina or clitoris, penis, and perineum.
[0276] Although the invention herein has been described with reference to
particular embodiments, it is to be understood that these embodiments are
merely illustrative of the principles and applications of the present
invention. It is therefore to be understood that numerous modifications
may be made to the illustrative embodiments and that other arrangements
may be devised without departing from the spirit and scope of the present
invention as defined by the appended claims.
* * * * *