Postinspiratory-ramp activity of diaphragm under inspiratory resistive load

Inspiratory ramp activity, postramp activity (PRA) of diaphragm and respiratory flow were studied in anesthetized rabbits and conscious humans under inspiratory resistive 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 SO2 block of slowly adapting stretch receptors in bronchi corresponding changes under load were nil and 65 +/- 7 msec. In humans 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 SO2 block) occurred during inspiration and that occurring during expiration was smaller than under control conditions. Consequently, under load braking of expiratory flow was smaller and peak expiratory flow occurred earlier than under control conditions.