What is the amount of gas that can be inhaled over and above that which is normally inhaled during quiet breathing?

The amount of gas that can be inhaled over and above what is normally inhaled during quiet breathing is referred to as Inspiratory Reserve Volume (IRV). During normal, quiet respiration, a person takes in a specific amount of air, known as tidal volume. IRV represents the additional air that can be inhaled after this tidal volume has been reached, emphasizing the capacity of the lungs to take in more air when needed, such as during physical activity or increased demand for oxygen.

In contrast, Expiratory Reserve Volume (ERV) pertains to the additional air that can be exhaled forcibly after a normal expiration. Functional Residual Capacity (FRC) indicates the volume of air remaining in the lungs after a normal expiration, consisting of both the ERV and Residual Volume. Vital Capacity (VC) is the total amount of air that can be exhaled after a maximum inhalation, incorporating tidal volume, IRV, and ERV.

Thus, the focus on IRV highlights its role in the lungs' ability to expand beyond normal quiet breathing to accommodate greater respiratory needs.