VT + IRV equals the:

The sum of tidal volume (VT) and inspiratory reserve volume (IRV) represents the inspiratory capacity. Inspiratory capacity is defined as the maximum amount of air that can be inhaled after a normal expiration, and it consists of the tidal volume, which is the volume of air inhaled or exhaled during each breathing cycle, plus the inspiratory reserve volume, which is the additional air that can be inhaled with a deep breath beyond the normal tidal volume.

Understanding how these volumes relate is key in pulmonary function testing. Tidal volume is a measure of a single breath, while inspiratory reserve volume quantifies the extra air that can be inhaled. By combining the two, you get the total amount of air that can be inhaled within a single respiratory cycle after normal expiration, hence categorizing it under inspiratory capacity.

The other options do not accurately reflect this sum:

• Functional residual capacity (FRC) includes both expiratory reserve volume and residual volume, not the tidal volume or IRV.

• Tidal volume is just the amount of air exchanged in a normal breath, and does not encompass reserves.

• Expiratory reserve volume is the volume of air that can be forcibly exhaled after the end of