The inspiratory reserve volume measures the
amount of air remaining in the lung after a maximal exhalation
amount of air that the lung holds
amount of air the can be further exhaled after a normal breath
amount of air that can be further inhaled after a normal breath

Amount of air that can be further inhaledafter a normal breath

Explanation:

The medical definition for inspiratory reserve volume or IRV is: "Amount of air that can be further inhaled after a normal inhalation".

As a color date, the mean IRV for adult men is 3.1lt, meaning more than the 50% for the lung capacity!

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