Functional residual capacity is composed of which of the following?

Functional residual capacity is composed of which of the following?

• A. Expiratory Reserve Volume and Residual Volume
• B. Inspiratory Reserve Volume and Residual Volume
• C. Expiratory Reserve Volume and Tidal Volume
• D. Expiratory Capacity and Tidal Volume

Answer: (A)

Functional residual capacity is the lung volume after a passive, normal exhalation. It comprises the air that remains in the lungs after that exhale (the residual volume) plus the extra air you could still exhale if you pushed out more air after the normal exhale (the expiratory reserve volume). So FRC = expiratory reserve volume + residual volume. Understanding the components helps: residual volume is the air that always stays in the lungs and cannot be measured by standard spirometry, while expiratory reserve volume is the additional amount you can forcibly exhale beyond a normal breath. The other options mix volumes that do not define this resting lung volume—such as inspiratory reserve volume, which is the extra air you can inhale after a normal inhalation, or tidal volume, which is the amount of air moved with a normal breath. Adding ERV to tidal volume gives expiratory capacity, not functional residual capacity.

Functional residual capacity is the lung volume after a passive, normal exhalation. It comprises the air that remains in the lungs after that exhale (the residual volume) plus the extra air you could still exhale if you pushed out more air after the normal exhale (the expiratory reserve volume). So FRC = expiratory reserve volume + residual volume.

Understanding the components helps: residual volume is the air that always stays in the lungs and cannot be measured by standard spirometry, while expiratory reserve volume is the additional amount you can forcibly exhale beyond a normal breath. The other options mix volumes that do not define this resting lung volume—such as inspiratory reserve volume, which is the extra air you can inhale after a normal inhalation, or tidal volume, which is the amount of air moved with a normal breath. Adding ERV to tidal volume gives expiratory capacity, not functional residual capacity.