Functional residual capacity is best described as which of the following?

Functional residual capacity is best described as which of the following?

• A. Air at the end of normal respiration.
• B. Air remaining after maximal exhale.
• C. The volume exhaled in the first second.
• D. The volume that cannot be exhaled.

Answer: (A)

Functional residual capacity is the volume of air remaining in the lungs after a normal exhalation. At the end of a regular breath out, the lungs hold a stable amount of air because the outward recoil of the chest wall balances the inward recoil of the lungs. This resting lung volume equals the sum of the expiratory reserve volume (air you could exhale with a strong effort) and the residual volume (air that cannot be exhaled). Why the other descriptions don’t fit: after a maximal exhale you still have air left—the residual volume—but that isn’t FRC. the volume exhaled in the first second describes the rate of expulsion (FEV1), not the resting lung volume. and the volume that cannot be exhaled is the residual volume, not FRC.

Functional residual capacity is the volume of air remaining in the lungs after a normal exhalation. At the end of a regular breath out, the lungs hold a stable amount of air because the outward recoil of the chest wall balances the inward recoil of the lungs. This resting lung volume equals the sum of the expiratory reserve volume (air you could exhale with a strong effort) and the residual volume (air that cannot be exhaled).

Why the other descriptions don’t fit: after a maximal exhale you still have air left—the residual volume—but that isn’t FRC. the volume exhaled in the first second describes the rate of expulsion (FEV1), not the resting lung volume. and the volume that cannot be exhaled is the residual volume, not FRC.