The Opposing Force of Pulmonary Elastance or Compliance
The lung is an elastic structure with an anatomical organization that promotes its collapse to essentially zero volume, much like an inflated balloon. The term elastic means a material deformed by a force tends to return to its initial shape or configuration when the force is removed. While the elastic properties of the lung are important to bring about expiration, they also oppose lung inflation. As a result, lung inflation depends upon contraction of the inspiratory muscles. How easily a lung inflates will relate to the compliance of the lung. Recall that the resistance to deformation (inflation) is termed elastance. However, compliance is the preferred term to describe the elastic properties of the lung. Compliance, as the recripocal of elastance, is a measure of the ease of deformation (inflation) (see animation).