Regarding lung volumes, which of the following is true: March 2009

Ans. B: Residual volume keeps alveoli inflated between breaths The amount of air that moves into the lungs with each inspiration (or the amount that moves out with each expiration) is called the tidal volume (500 ml). The air inspired with a maximal inspiratory effo in excess of the tidal volume is the inspiratory reserve volume. (3000 ml) The volume expelled by an active expiratory effo after passive expiration is the expiratory reserve volume (1200 ml), and the air left in the lungs after a maximal expiratory effo is the residual volume (1200 ml). The space in the conducting zone of the airways occupied by gas that does not exchange with blood in the pulmonary vessels is the respiratory dead space. The vital capacity (4700 ml), the largest amount of air that can be expired after a maximal inspiratory effo, is frequently measured clinically as an index of pulmonary function. It gives useful information about the strength of the respiratory muscles and other aspects of pulmonary function (ERV+TV+IRV) The fraction of the vital capacity expired during the first second of a forced expiration (FEV1, timed vital capacity) gives additional information; the vital capacity may be normal but the FEV1 reduced in diseases such as asthma, in which airway resistance is increased because of bronchial constriction. The amount of air inspired per minute (pulmonary ventilation, respiratory minute volume) is normally about 6 L (500 mL/ breath x 12 breaths/ min). The maximal voluntary ventilation (MVV), or, as it was formerly called, the maximal breathing capacity, is the largest volume of gas that can be moved into and out of the lungs in 1 minute by voluntary effo. The normal MVV is 125-170 L/ min. Inspiratory Capacity (TV + IRV) = 3500 ml Functional Residual Capacity (RV + ERV) = 2400 ml Total Lung capacity (RV + VC) = 5900 ml