Postinspiratory-ramp activity of diaphragn under inspiratory resistive load

Abstract

Inspiratory ramp activity, postramp acitivity (PRA) of diaphragm and respiratory flow were studied in anesthetized rabbits and conscious humans under inspiratory resisitive load. Under load with chloralose-urethane anesthesia neural inspiration lasted 124±12 msec more than under control conditions and end of mechanical inspiration lagged behind that of neural inspiration by 114±4 msec. With pentobarbital-urethane anesthesia corresponding changes under load were 67±18 msec and 44±6 msec; after SO 2 block of slowly adapting stretch receptors in bronchi corresponding changes under load were nil and 65±7 msec. In human corresponding changes under load were about 192 and 127 msec. Both in rabbits and humans time course of PRA under load was essentially unchanged. Hence, under load a considerable part of PRA (or all of it under pentobarbital-urethane anesthesia without SO 2 block) occured during inspiration and that occuring during expiration was smaller than under control conditions. Consequently, under load braking of expiratory flow was smaller and peak expiratory flow occured earlier than under control conditions.