What is the term for the air remaining in the lungs after forced expiration?

The correct choice refers to residual volume, which is the amount of air that remains in the lungs after a person has exhaled forcefully. This volume is crucial for maintaining some level of gas exchange and preventing the lungs from collapsing by ensuring that the alveoli are always partially inflated. Residual volume plays a vital role in sustaining oxygen levels in the blood and is a necessary component of lung function.

While tidal volume refers to the amount of air inhaled or exhaled during a normal breath, functional residual capacity includes both the residual volume and the expiratory reserve volume (the extra air that can be expelled after a normal expiration). Vital capacity, on the other hand, measures the maximum amount of air that can be exhaled after maximum inhalation and does not account for the air left in the lungs after forced expiration. Thus, residual volume is specifically focused on what remains in the lungs after exhalation, distinguishing it from these other respiratory volume measures.