What lung volume is measured during a lung function test to assess reserve capacity?

Functional Residual Capacity (FRC) is the lung volume measured to assess reserve capacity. FRC represents the volume of air that remains in the lungs at the end of a normal expiration. This volume includes both the expiratory reserve volume and the residual volume. Assessing FRC is important because it provides insight into the lungs' ability to sustain gas exchange and maintain adequate oxygenation. An appropriate FRC allows for a reserve of air to be available during periods of increased respiratory demand.

In contrast, Inspiratory Reserve Volume (IRV) refers to the maximum volume of air that can be inhaled beyond a normal tidal breath, which does not reflect the lung's reserve under normal conditions. Tidal Volume (TV) is simply the amount of air inhaled or exhaled during a normal breath and does not provide a measure of reserve. Vital Capacity (VC) measures the maximum amount of air that can be exhaled after a maximum inhalation, representing the total capacity available for breathing but not specifically addressing reserve capacity like FRC does.