What volume is measured when a patient maximally exhales after passively exhaling normal tidal volume?

The volume measured when a patient maximally exhales after passively exhaling their normal tidal volume is known as the expiratory reserve volume (ERV). This volume represents the amount of air that can be forcibly exhaled from the lungs following a normal passive exhalation.

In the context of lung volumes, tidal volume refers to the amount of air inhaled or exhaled during normal breathing. After completing a normal tidal exhalation, the patient can then exhale forcefully, which quantifies the expiratory reserve volume. This volume is important in assessing respiratory function, particularly in conditions that affect the mechanics of ventilation.

Other lung volumes mentioned in the options are distinct from ERV. Vital capacity (VC) includes tidal volume, inspiratory reserve volume, and expiratory reserve volume but not the residual volume or any air remaining in the lungs after maximal exhalation. Total lung capacity (TLC) encompasses all the volumes of air in the lungs, and functional residual capacity (FRC) consists of the volume of air remaining in the lungs after normal exhalation, which includes both the expiratory reserve volume and the residual volume.