What is the result of adding Expiratory Reserve Volume (ER) and Residual Volume (RV)?

Combining Expiratory Reserve Volume (ER) and Residual Volume (RV) results in Functional Residual Capacity (FRC).

FRC is defined as the volume of air remaining in the lungs after a normal expiration. It reflects the amount of air that is available for gas exchange at the end of a tidal breath. Expiratory Reserve Volume is the additional amount of air that can be forcibly exhaled after the end of a normal expiration, while Residual Volume is the air that remains in the lungs after a person has exhaled as much as possible. When you add these two volumes together, you account for all the air that remains in the lungs after a standard expiration, aligning perfectly with the definition of FRC.

The other options represent different lung capacities: Total Lung Capacity (TLC) includes all lung volumes; Forced Vital Capacity (FVC) involves maximal inhalation followed by a forced exhalation, which does not directly involve the combination of ER and RV; and Residual Volume (RV) is just one component of FRC and does not take into account the added volume from the ER. Thus, the correct answer encapsulates the concept of lung volumes and their contribution to functional capacity within the respiratory system