What is functional residual capacity?

What is functional residual capacity?

• A. End of maximal inspiration.
• B. Air at the end of normal respiration.
• C. The amount of air in the lungs after a full expiration.
• D. Volume moved per minute.

Answer: (B)

Functional residual capacity is the amount of air left in the lungs after a normal, quiet exhalation. It represents the resting lung volume where the inward recoil of the lungs and the outward recoil of the chest wall balance each other, and it equals the expiratory reserve volume plus the residual volume. This description matches “Air at the end of normal respiration,” making it the best choice. After a maximal inhalation you reach total lung capacity, not FRC; after a full expiration you approach residual volume; and volume moved per minute refers to ventilation rate, not a static lung volume.

Functional residual capacity is the amount of air left in the lungs after a normal, quiet exhalation. It represents the resting lung volume where the inward recoil of the lungs and the outward recoil of the chest wall balance each other, and it equals the expiratory reserve volume plus the residual volume. This description matches “Air at the end of normal respiration,” making it the best choice. After a maximal inhalation you reach total lung capacity, not FRC; after a full expiration you approach residual volume; and volume moved per minute refers to ventilation rate, not a static lung volume.