Which statement defines residual volume (RV)?

Which statement defines residual volume (RV)?

• A. Residual volume is the maximum amount of air in the lungs at the end of maximal inspiration.
• B. The amount of air remaining in the lungs after maximum expiration that cannot be voluntarily exhaled.
• C. The maximum amount of air that can be inhaled following a normal expiration.
• D. The amount of air remaining in the lungs after a normal expiration.

Answer: (B)

Residual volume is the amount of air left in the lungs after a maximal expiration that cannot be voluntarily exhaled. This air keeps the airways open and prevents alveolar collapse between breaths, so some gas exchange can continue even between breaths. That makes it the best definition among the options. The other statements describe different lung volumes. The amount of air in the lungs at the end of a maximal inspiration is the total lung capacity, not residual. The maximum air that can be inhaled after a normal expiration is inspiratory capacity, not the residual. And the air remaining after a normal expiration is the functional residual capacity, which equals the sum of expiratory reserve volume and residual volume, not just the residual alone.

Residual volume is the amount of air left in the lungs after a maximal expiration that cannot be voluntarily exhaled. This air keeps the airways open and prevents alveolar collapse between breaths, so some gas exchange can continue even between breaths. That makes it the best definition among the options.

The other statements describe different lung volumes. The amount of air in the lungs at the end of a maximal inspiration is the total lung capacity, not residual. The maximum air that can be inhaled after a normal expiration is inspiratory capacity, not the residual. And the air remaining after a normal expiration is the functional residual capacity, which equals the sum of expiratory reserve volume and residual volume, not just the residual alone.