Anesthesia and Changes in Lung Volume

Abstract

Perhaps the most fundamental effect of anesthesia on the respiratory system is the decrease of the functional residual capacity. The cause of this change probably lies in the effect of anesthesia on the respiratory muscles. During normal breathing by the conscious subject in the supine position, the diaphragm retains considerable tone at the end of expiration. This holds the lung volume above that which it would attain if determined solely by the equilibration of elastic forces. This may well be a special mechanism to prevent the weight of the viscera pushing the diaphragm too far into the chest in the supine position. Muller and his colleagues (1) have used diaphragmatic electromyography to demonstrate that this residual end-expiratory tone is lost during anesthesia with halothane.