Compliance is defined as:

• A. the ability for the alveoli to expand during inhalation
• B. the movement of gas from high to low concentration
• C. the exchange of gases between blood and tissues
• D. the amount of expired carbon dioxide

Answer: (A)

Compliance reflects how easily the lungs can expand during inhalation. The best description is the alveoli’s ability to expand, which shows lung distensibility and how much volume you get for a given pressure change. Diffusion is about gas moving from high to low concentration, not about how stretchy the lung tissue is. Gas exchange between blood and tissues involves perfusion and diffusion at the tissue level, not lung stretch. The amount of expired carbon dioxide measures ventilation and CO2 elimination, not structural stretch of the lungs. In practice, higher or lower compliance affects how much air you can deliver with a given pressure, influencing how you manage ventilation during airway procedures.