By Kathe G. Henke, PhD, and Amanda J. Piper, PhD
Use of continuous positive airway pressure to splint open the upper airway in patients with obstructive sleep apnea may seem obvious and routine to those of us now working in the area of sleep and breathing. But two decades ago, effective treatment for OSA was limited to tracheostomy.
On the 20th anniversary of the invention of CPAP, we spoke to Colin Sullivan, PhD, BSc(Med), MB, FRACP, of Sydney, Australia, who first conceived of using nasal CPAP for treating obstructive sleep apnea, to see how it all started. This is how he remembers it:
Q: How did you first come up with the idea for nasal CPAP?
A: "After working with sleep researcher Eliot Phillipson in Toronto, I returned to Australia in 1979 and continued work on the upper airway using the dog model. I had a long-time interest in the upper airway, in particular its potential role in cot [crib] death.
"When I returned to Australia, my initial research focus was on measuring and comparing responses to nasal and tracheal occlusion in this animal model. As a consequence of performing these studies, we had become quite skilled in molding snout masks out of fiberglass for the dogs, and used a Silastic™ material to hold them in place. A little later on, I was joined by Faiq Issa and Michael Berthon-Jones, who worked with me on human subjects, looking at occlusion and ventilatory responses during sleep.
"In 1980, we had a meeting in Sydney that brought together researchers and clinicians from around the world to discuss the latest issues surrounding sleep and breathing. It was at that meeting that sleep pioneers Elliot Weitzman and Christian Guilleminault independently had produced really nice pictures, using fiber-optic scopes, of the upper airway closing during sleep. These pictures stimulated a great deal of discussion at this meeting as to whether we were seeing passive collapse or an active contraction of the upper airway muscles during sleep. We didn't have the answers, but I found the question fascinating.
"Over the next few weeks the mechanism behind upper airway obstruction during sleep really stayed on my mind. We continued our experiments on occlusion in sleeping humans during NREM and REM sleep, as well as studying ventilatory responses before and after tracheostomies.
"Then, one afternoon we were setting up for a nighttime study on a patient with severe OSA who was scheduled for a tracheostomy. He was participating in a series of nightly studies before and after the procedure to measure breathing during sleep. Discussing the issues with me, the patient was eager to know if there was anything else that might work. I suppose I was thinking out loud, looking at the mask and all the tubing sitting around for the experimental procedure, when it occurred to me that putting pressure in the upper airway might just hold it open.
"The patient was keen to give it a try, and so at [3:30 p.m.] we started searching around for equipment that we could use. We had large bore tubing into which we cut holes for nasal prongs to fit into. We then used plenty of Silastic glue to hold the nasal piece in place. Our next problem was sourcing a blower to create an appropriate pressure. We had a blower we used to calibrate the Fleish pneumotach and thought that might work. So, in a couple of hours, the first nasal CPAP device for OSA was born.
"We were very tentative going into this, not knowing what would happen, how the patient might respond or even if we might 'blow the patient up.' Our initial plans were simply to record sleep and breathing for a short time with the blower on to see what would happen and then continue with the scheduled experiments.
"What we weren't prepared for was how quickly and easily we were able to unblock the upper airway obstruction. As we turned the pressure up, the obstruction disappeared, and the patient went immediately into REM. We then reduced the pressure and recreated the classic obstructive pattern that we had seen the night before. Turning the pressure up again relieved the obstruction.
"After a few runs of switching the apnea on and off by changing the pressure level, we realized what a fantastic physiological tool we now had to study obstructive sleep apnea and mechanisms. However, it wasn't obvious to me at this stage that this could be a long-term treatment for the patient. I was excited by all the experiments we could now perform.
"Although we initially had planned to use the pressurized system for just a short time during that first night, the impressive response in terms of sleep quality and respiratory, as well as the patient's tolerance to it, made me decide to continue on for the whole night. After all, just because it worked for five minutes, it didn't mean it would work for five hours.
"You have to remember, 20 years ago we knew the airway was collapsing, but no one knew why. Was this passive collapse, or was it an active response? I reasoned that if what we were seeing was a reflexive response, then adaptation to the continuous pressure would occur over time. On the other hand, if it was a physical problem of passive collapse, then CPAP would act as a splint and no adaptation would be seen.
"I realized that we could answer that question by the end of the night. So we continued with pressurization for the rest of the night. And we had an extremely satisfied and rested patient next morning. The results we saw were absolutely clear-cut, and I knew straight away that the upper airway obstruction was a passive process simply by how easy it was to unobstruct the airway."
Q: At the time, did you realize just how revolutionary these findings were?
A: "I was really excited that first night. By [4 a.m.] I'd already drafted a case report, ready to get it off to a journal the next day. But a little later I realized the potential significance of our finding and decided to wait until we had the opportunity to gather more data.
"Initially, I saw this whole technique as a phenomenal research tool, giving us the opportunity to turn upper airway obstruction on and off at will, and measuring various responses to it, without invasively altering the airway itself. So, to begin with, we simply went head-on into the experimental side of things, and it took several patients before we realized that this could be something they would be willing to use longer-term at home.
"In fact, the first patient we sent home on the treatment was really a result of the patient's own insistence that he be allowed to give it a try. He had loved it during the experimental procedures and wanted to try anything rather than undergo a tracheostomy. So it was really the patients who showed us they would be willing to use this long-term, and our job was to work out how to do that. So CPAP moved from being just an interesting and powerful experimental tool to an effective and acceptable home treatment.
"Despite the cumbersome nature of the early equipment we put together, the concept of gluing a mask on the face and attaching it to a blower at home was well received by most patients. After all, no matter how funny it looked at 10 p.m., the patient could remove it all the next morning with no sign of what had gone on. The alternative for them was a permanent tracheostomy. We initially told patients we didn't know how long this therapy would work and that surgery in the future was still an option."
Q: What kind of equipment was first used?
A: "We actually made the first blowers using a two-stage vacuum cleaner motor that we modified for home use. We tried a whole range of head harnesses, but one of the earliest setups that worked was using the inside of a bicycle helmet to hold the mask in place. We also individually molded masks and provided patients with large pots of Silastic paste and catalyst to glue the masks on. We later accessed the Vortex blower motor, which was designed for dental drills, and these worked really well for home use and were easily accessible.
"In 1981, Jim Bruderer, a Swiss-born toolmaker, joined our team, and he was responsible for many of the technological improvements in the equipment and mask for home use. By 1984, we were beginning to move away from the individually molded masks. From just a couple of patients on home treatment in 1980, by 1985 we had more than 100 patients at home on CPAP therapy."
CPAP has come a long way since those first research nights in 1980. Improvements in mask and machine design have increased patient comfort and acceptance of CPAP. Other technological advancements such as bilevel pressure, auto-adjusting CPAP, humidification and compliance monitoring have expanded the usefulness of CPAP for the clinician as well as for individuals with sleep apnea.
Authors' note: The original paper describing these first individuals treated with nasal CPAP was published in: Sullivan CE, Issa FG, Berthon-Jones M, Eves L. Reversal of obstructive sleep apnea by continuous positive airway pressure applied through the nares. Lancet. 1981;1:862-65.
A member of the American Sleep Apnea Association board of directors, Dr. Henke is at the Sleep Disorders Center of Virginia and did her post-doctoral training with Dr. Sullivan. Dr. Piper is senior physiotherapist, Centre for Respiratory Failure and Sleep Disorders at the University of Sydney, Australia.
Sleep Tracks, Advance for Managers of Respiratory Care, December, 2001.
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