Which of the following statements is true about Residual Volume (RV)?

Residual Volume (RV) refers to the amount of air that remains in the lungs after a person has exhaled as forcefully as possible. This volume is important because it prevents the alveoli (air sacs in the lungs) from collapsing completely and ensures that there is always some air in the lungs available for gas exchange.

The statement that RV is the air left after Expiratory Reserve Volume (ERV) has been used accurately reflects this concept. Expiratory Reserve Volume is the additional amount of air that can be exhaled after a normal tidal expiration. After using up the ERV, the volume of air that remains in the lungs is the Residual Volume. This understanding is crucial for evaluating lung function and overall respiratory health, especially in clinical settings.

The incorrect options present misunderstandings about RV's role and quantification in lung physiology. For instance, while it is true that RV exists in the lungs after exhaling, it is not defined as the amount that can be forcefully exhaled, nor does it constitute a specific percentage of Total Lung Capacity. Furthermore, RV cannot be voluntarily exhaled; it is inherently non-exchangeable air that remains in the lungs regardless of respiratory effort. This distinction emphasizes the unique role