Inspiratory reserve volume, or IRV, is the air a person can forcefully inhale following a normal quiet breath, which is about 2.5 to 3.5 liters, according to class notes from the College of Science and Mathematics at James Madison University. It is the additional amount of air a person can bring into his lungs upon inhaling deeply.
The process of respiration includes air moving in and out of the lungs. This air is measured in volume. As a person inhales, his thoracic cavity expands, which sucks air into the lungs. As a person exhales, air is pushed out of the lungs. The air that moves in and out of the lungs during normal inspiration, such as when a person is at rest, is called tidal volume. Tidal volume is about 0.5 liters, explains class notes from the College of Science and Mathematics at James Madison University.
In addition to the tidal volume, a person is able to force about 2.5 to 3.5 more liters of air into the lungs by breathing in more deeply. This extra volume of air is the inspiratory reserve volume. When a person breathes out, he is able to force out approximately 1 more liter of air. This extra volume of air is called the expiratory reserve volume. There is always some air in the lungs, even after a forceful expiration. This is called the residual volume and it is about 1 liter, states class notes from the College of Science and Mathematics at James Madison University.