How is functional residual capacity calculated?

Functional residual capacity (FRC) is a key measurement in respiratory physiology that represents the volume of air remaining in the lungs at the end of a normal expiration. It is calculated by adding the residual volume (RV) to the expiratory reserve volume (ERV).

Residual volume is the amount of air that remains in the lungs after a forceful expiration and cannot be exhaled. On the other hand, expiratory reserve volume is the additional air that can be forcibly exhaled after the end of a normal tidal expiration. When these two volumes are combined, they provide a comprehensive measure of the air that is available in the lungs for gas exchange after passive breathing has taken place.

This measurement is crucial for assessing lung function and can provide insights into various pulmonary conditions. The other options refer to combinations of volumes that do not yield FRC, as they involve tidal volume (TV) or inspiratory capacity (IC), which are not components in the definition of functional residual capacity.