Which property describes the lungs' tendency to return to their original shape after expansion?

• A. Elastance
• B. Compliance
• C. Baseline Pressure
• D. Tissue Resistance

Answer: (A)

Elastance is the lungs’ tendency to snap back to their original shape after expansion. It describes how much pressure is needed to return a given amount of stretched volume, and it’s the reciprocal of compliance. A high elastance means the lungs recoil strongly and are stiff, so they tend to return to resting volume quickly after inflation. Compliance, by contrast, is about how easily the lungs expand for a given pressure, i.e., their distensibility, not how they recoil. Baseline pressure refers to the resting airway pressure at end expiration and isn’t a measure of recoil, while tissue resistance describes how strongly air flow is opposed by the airways and tissues, not the lung’s elastic return. So the property that captures the curl-back of the lung after expansion is elastance.