Which statement best describes high vs low lung compliance?

• A. High compliance means easier to fill; Low compliance requires greater force to fill
• B. High compliance means lungs fill easily; Low compliance means easier to fill
• C. High compliance indicates reduced elasticity and high recoil
• D. High compliance only occurs in diseased lungs

Answer: (A)

Lung compliance reflects how easily the lungs expand for a given pressure change. It’s the change in volume per unit change in transpulmonary pressure. When compliance is high, the lungs stretch easily, so a small pressure increase yields a large volume change and filling is easy. When compliance is low, the lungs are stiff and require a much larger pressure change to achieve the same volume change, making inflation harder and requiring more force. So the best description is that high compliance means the lungs fill easily, while low compliance requires greater force to fill. High compliance is associated with reduced elastic recoil; low compliance with increased elastic recoil. Emphysema increases compliance; fibrosis decreases it. The other statements mix up these relations or claim limits to disease, which isn’t accurate.