Effects of Anesthesia and Muscle Paralysis on the Mechanics of the Respiratory System

Abstract

Ventilation of the lungs depends on the duration and strength of efferent neural stimuli from the respiratory center, the contracting force of the respiratory muscles resulting from these stimuli, and the mechanical characteristics of the respiratory system. In studying the control of respiration during general anesthesia, changes in the force of contraction of the respiratory muscles and in the impedance of the respiratory system must be considered. For example, the performance of the diaphragm depends on lung volume. Hence, a reduction in functional residual capacity (FRC) , as occurs during general anesthesia, if accompanied by a change in the configuration of the diaphragm, may increase the efficiency of the diaphragm as a pressure generator, and the ventilatory response to a given neural stimulus may be increased. If the impedance of the respiratory system increases during general anesthesia, a decrease of ventilation for a given pressure change may be expected. Recently, it was suggested that much of the decrease in ventilation during general anesthesia with methoxyflurane is caused by the increased impedance of the respiratory system¹.