What describes the amount of air remaining in the lungs after a forced exhalation?

Residual volume refers to the amount of air that remains in the lungs after a person has exhaled forcefully. This volume is crucial because it prevents the lungs from collapsing completely and ensures that gas exchange can continue even between breaths. By retaining a certain volume of air, the lungs maintain adequate levels of oxygen and help prevent fluctuations in the concentration of gases in the blood.

Other related terms include vital capacity, which is the maximum amount of air that can be exhaled after taking the deepest breath possible, and inspiratory reserve volume, which is the additional amount of air that can be inhaled after a normal inhalation. Dead space ventilation refers to air that does not participate in gas exchange because it resides in the trachea and bronchi, rather than the alveoli. Understanding these definitions highlights why residual volume specifically denotes the air left in the lungs after a forced exhalation.