The total lung capacity of a patient is 5.5 liters. Find the patient’s inspiratory reserve volume if the patient’s vital capacity was 4.2 liters, the tidal volume was 500 ml, and the expiratory reserve volume was 1.2 liters. Solution Answer: Inspiratory reseve volume (IRV )= VC - (TV + ERV) VC= Vital capacity TV= Tidal volume ERV= Expiratory reseve volume = 4.2- (0.5 + 1.2) = 2.5 Liters.