What is the equation for vital capacity (VC)?

Vital capacity (VC) refers to the maximum amount of air that can be exhaled after a maximum inhalation. It is an important measure in assessing lung function and consists of three key components of lung volume: tidal volume (VT), inspiratory reserve volume (IRV), and expiratory reserve volume (ERV).

Tidal volume (VT) is the amount of air inhaled or exhaled during regular breathing. Inspiratory reserve volume (IRV) represents the additional amount of air that can be inhaled after a normal inhalation, while expiratory reserve volume (ERV) is the additional air that can be forcibly exhaled after a normal exhalation. The equation for vital capacity is the sum of these three volumes:

VC = VT + IRV + ERV.

This sum captures the full range of ventilatory capacity available to an individual, thereby providing a useful indication of respiratory health. Other volumes included in the options, such as residual volume (RV) or functional residual capacity (FRC), do not contribute to vital capacity, as residual volume refers to the air remaining in the lungs after maximal exhalation and is not actively involved in the exchange of gases during breathing. Thus, the components correctly adding up to