Final answer:
The inspiratory reserve volume (IRV) is the extra volume that can be maximally inspired above quiet breathing.
Step-by-step explanation:
The inspiratory reserve volume (IRV) is the extra volume of air that can be maximally inspired above quiet breathing. It is produced by a deep inhalation, past a normal tidal inspiration. Unlike the tidal volume, which measures the amount of air entering/leaving the lungs during a single breath, the inspiratory reserve volume represents the extra amount of air that can be inhaled after a normal inhalation.