THE EFFECT OF AMINOPHYLLINE ON THE FORCE-LENGTH CHARACTERISTICS OF THE DIAPHRAGM

The aim of our study was to evaluate the effect of aminophylline on th e contractile function of the human diaphragm during varying muscle fi ber length. Ten healthy subjects were studied during maximal sniff man euvers and bilateral phrenic nerve twitch stimulations, with and witho ut intravenous infusion of aminophylline in a randomized fashion. The transdiaphragmatic pressures generated at various baseline lung volume s, from residual volume to 90% of total lung capacity, were recorded b efore and after the induction of diaphragm exhaustion. At all levels o f lung volume, aminophylline did not have an effect on the contractili ty of the fresh diaphragm. In the exhausted diaphragm, however, the pr essure values, induced by sniffs and twitch stimulations, were signifi cantly improved by aminophylline. This positive effect on diaphragm co ntractility was also impressive at 60, 75, and 90% of total lung capac ity. This indicates that aminophylline significantly improves the cont ractile function of the exhausted human diaphragm, even if the muscle fibers are shorter than optimal. This effect occurs regardless of the neuronal firing rate, whether it is low (twitch stimulation) or high ( sniff maneuver).