Question

Functional residual capacity is the volume of air in the lungs measured?

• A. After normal inspiration
• B. After normal expiration
• C. After forceful expiration
• D. After forceful inspiration

Hint:

FRC is the resting lung volume left at the end of a quiet, passive breath out.

Answer 1

The Correct Option is B

Step 1: Functional residual capacity (FRC) is the volume of air remaining in the lungs at the end of a normal, passive (quiet) expiration.
Step 2: At this point the inward elastic recoil of the lung is balanced by the outward recoil of the chest wall, so it is the resting equilibrium volume of the respiratory system. FRC equals expiratory reserve volume plus residual volume.
Step 3: Therefore FRC is measured after a normal (tidal) expiration - option b.
Step 4: After normal inspiration (a) gives a larger volume, not FRC. After forceful expiration (c) gives the residual volume only. After forceful inspiration (d) gives total lung capacity. The defining point for FRC is the end of quiet expiration.