Pulmonary function tests: Lung volumes and capacities

These are boundaries of lung volume within which tidal volume can vary. A lung capacity is a combination of more than one lung volume. TLC, for example, is the combination of FRC plus IC (or the combination of RV, ERV, VT, and IRV). TLC, RV, and their ratio provide the most information about restrictive lung disease and help differentiate between restrictive and obstructive disorders. However, TLC and RV are effort-dependent, so an evaluation of strength and/or effort is needed. In contrast, the FRC is effort-independent.