Functional residual capacity is defined as which of the following?

Functional residual capacity is defined as which of the following?

• A. The total amount of air in the lungs after maximal inspiration
• B. The volume of air remaining after maximal expiration
• C. The volume in the lungs at the end of a normal exhalation (ERV + RV)
• D. The air moved in and out during a normal breath

Answer: (C)

Functional residual capacity is the amount of air left in the lungs after you exhale normally. This resting volume exists because the lungs tend to recoil inward while the chest wall tends to spring outward, creating a balance point. FRC equals the expiratory reserve volume plus the residual volume, so after a normal exhale you have ERV + RV in the lungs. That’s why the volume at the end of a normal exhalation is FRC. The other terms describe different lung volumes: the total air after a maximal inspiration is the total lung capacity, the volume remaining after a maximal expiration is the residual volume, and the air moved in and out during a normal breath is the tidal volume.

Functional residual capacity is the amount of air left in the lungs after you exhale normally. This resting volume exists because the lungs tend to recoil inward while the chest wall tends to spring outward, creating a balance point. FRC equals the expiratory reserve volume plus the residual volume, so after a normal exhale you have ERV + RV in the lungs. That’s why the volume at the end of a normal exhalation is FRC. The other terms describe different lung volumes: the total air after a maximal inspiration is the total lung capacity, the volume remaining after a maximal expiration is the residual volume, and the air moved in and out during a normal breath is the tidal volume.