Physiology, Residual Volume

Residual volume (RV) is the volume of air remaining in the lungs after maximum forceful expiration. In other words, it is the volume of air that cannot be expelled, thus causing the alveoli to remain open at all times. The residual volume remains unchanged regardless of the lung volume at which expiration was started. Reference values for residual volume are 1 to 1.2 L, but these values are dependent on factors including age, gender, height, weight, and physical activity levels.The residual volume is an important component of the total lung capacity (TLC) and the functional residual capacity (FRC). TLC is the total volume of the lungs at maximal inspiration which is about 6 L on average, though true values are dependent on the same factors that affect residual volume. FRC is the amount of air remaining in the lungs after a normal, physiologic expiration (Figure 1A). The TLC, FRC, and RV are absolute lung volumes and cannot be measured directly with spirometry. Instead, they must be calculated using indirect measurement techniques such as gas dilution or body plethysmography. Calculating the residual volume can give an indication of lung physiology and pathology.