Respiratory Volumes and Capacities

Four basic respiratory volumes are recognised. Tidal volume (TV) is the volume of air moved in or out with each normal, quiet breath - about 500 mL, giving a normal adult a total air movement of roughly 6000-8000 mL per minute; during vigorous exercise, tidal volume can rise to 4-10 times this value. Inspiratory reserve volume (IRV) is the extra air (about 2500-3000 mL) that can still be pulled in by a maximal forced inspiration after a normal tidal inspiration. Expiratory reserve volume (ERV) is the extra air (about 1000-1100 mL) that can still be pushed out by a maximal forced expiration after a normal tidal expiration. Residual volume (RV) is the air (about 1100-1200 mL) that always remains in the lungs even after the most forceful possible expiration, since the lungs can never be completely emptied.

Respiratory capacities are simply sums of two or more of these volumes. Vital capacity (VC = TV + IRV + ERV) is the maximum volume that can be moved in a single breath after a maximal inspiration followed by a maximal expiration. Inspiratory capacity (IC = TV + IRV) is the total volume that can be inhaled starting from the end of a normal, quiet expiration. Expiratory capacity (EC = TV + ERV) is the total volume that can be exhaled starting from the end of a normal, quiet inspiration. Functional residual capacity (FRC = ERV + RV) is the volume remaining in the lungs after a normal, quiet expiration. Total lung capacity (TLC = VC + RV), about 6000 mL, is the maximum volume the lungs can hold after the deepest possible inspiration. …