[The central and peripheral components of respiratory muscle fatigue during inspiratory resistive loading in cats].

In 18 anesthetized cats, electrical activity of diaphragmatic nerve, external intercostal muscles and diaphragm, was monitored. Starting from a certain level of inspiratory load, the transdiaphragmatic pressure and the diaphragm EMG decreased, the efferent activity of diaphragmatic nerve remaining the same. This data suggests a peripheral character of diaphragmatic muscle exhaustion related to disorders in neuromuscular transmission. Further exposure to hard mechanical load entails a decrease in diaphragmatic nerve electrical activity, too, thus indicating a development of central exhaustion of respiratory muscles, diaphragm in particular. The decrease in diaphragmatic nerve electrical activity may be related to excessive afferentation from the respiratory muscles mechanoreceptors, peripheral and central chemoreceptors leading to a "satiation" of inspiratory neurons of dorsal respiratory muscles; the hypoxic factor and the effect of endogenous physiologically active substances cannot be excluded either.