Decay rate of inspiratory muscle pressure during expiration in man

Abstract

Decay rate of inspiratory muscle pressure (Pmus 1) was studied in 4 subjects during post-inspiratory period of zero flow (T Ez) occuring discontinuous inspiratory elastic load (DIL). End-inspiratory pressure (Pmus eI) was increased by dead spaces or excercise. Decay rate was related to Pmus eI by a power function with exponent >1. It was not directly affected by concomitant changes of P CO 2 . It did not increase when an expiratory resistive load was added, i.e. when braking action of inspiratory muscles was no longer required. Time course of Pmus 1 during T Ez was more straight than exponential. Relative decay rate increased with Pmus eI and with decrease of inspiratory or expiratory time. Experiments with resistive loads suggest that relative rate is mainly related to timing factors. During voluntary inspiratory efforts with closed airways, relatively decay rate was not related to Pmus eI, while decay rate increased linearly with Pmus eI.