Regarding functional residual capacity, which statement is true?

Regarding functional residual capacity, which statement is true?

• A. FRC equals RV + ERV.
• B. FRC equals TV + IRV.
• C. FRC equals RV + VC.
• D. FRC equals TLC.

Answer: (A)

Functional residual capacity is the amount of air remaining in the lungs after a normal exhalation. It consists of the air you cannot exhale (residual volume) plus the extra air you could exhale if you were to force a deeper expiration after a normal breath (expiratory reserve). Because of this, FRC equals RV plus ERV. The other expressions mix different lung-volume components: tidal volume plus inspiratory reserve is the inspiratory capacity, not FRC; residual volume plus vital capacity would be a larger total than FRC; and total lung capacity is the volume after a maximal inhalation, not the volume after a normal exhalation.

Functional residual capacity is the amount of air remaining in the lungs after a normal exhalation. It consists of the air you cannot exhale (residual volume) plus the extra air you could exhale if you were to force a deeper expiration after a normal breath (expiratory reserve). Because of this, FRC equals RV plus ERV.

The other expressions mix different lung-volume components: tidal volume plus inspiratory reserve is the inspiratory capacity, not FRC; residual volume plus vital capacity would be a larger total than FRC; and total lung capacity is the volume after a maximal inhalation, not the volume after a normal exhalation.