Journal of Applied Physiology, Vol 54, Issue 2 475-482, Copyright © 1983 by American Physiological Society
Respiratory muscle function during CO2 rebreathing with inspiratory flow-resistive loading
M. Lopata, E. Onal and A. S. Ginzburg
We investigated the respiratory muscle contribution to inspiratory load
compensation by measuring diaphragmatic and intercostal electromyograms
(EMGdi and EMGic), transdiaphragmatic pressure (Pdi), and thoracoabdominal
motion during CO2 rebreathing with and without 15 cmH2O X l-1 X s
inspiratory flow resistance (IRL) in normal sitting volunteers. During IRL
compared with control, Pdi measured during airflow and during airway
occlusion increased for a given change in CO2 partial pressure and EMGdi,
and there was a greater decrease in abdominal (AB) end expiratory
anteroposterior dimensions with increased expiratory gastric pressure
(Pga), this leading to an inspiratory decline in Pga with outward AB
movement, indicating a passive component to the descent of the
abdomen-diaphragm. The response of EMGic to IRL was similar to that of
EMGdi, though rib cage (RC)-Pga plots did infer intercostal muscle
contribution. We conclude that during CO2 rebreathing with IRL there is
improved diaphragmatic neuromuscular coupling, the prolongation of
inspiration promoting a force-velocity advantage, and increased AB action
serving to optimize diaphragm length and configuration, as well as to
provide its own passive inspiratory action. Intercostal action provides
increased assistance also. Therefore, compensation for inspiratory
resistive loads results from the combined and integrated effort of all
respiratory muscle groups.
