Effects of expiratory resistive load on respiratory motor output in conscious humans

We examined, in five conscious human subjects, the steady-state effects of expiratory resistive loading (ERL; R = 8 cmH2O.l-1.s) on the time course of inspiratory and postinspiratory muscle activities (IA and PIA, respectively) and ventilatory pattern during quiet breathing. Driving pressure (DP) was calculated by means of a respiratory neuromechanical model (J. Appl. Physiol. 51: 963-989, 1981) that permitted the derivation, from tidal volume and flow, of the occlusion pressure equivalent (at functional residual capacity) of respiratory neural output throughout the breath. ERL caused a prolongation of both neural inspiratory duration (12.2 +/- 6.9% SD) and expiratory duration (25.0 +/- 10.1%) and an increase in the amplitude of DP (16.5 +/- 10.2%) without any changes in the waveshape of IA and in end-expiratory level. The relative time course of PIA was not altered by ERL. Minute ventilation was depressed (-6.75 +/- 2.88%) during ERL with little change in alveolar PCO2. The results indicate that pulmonary gas exchange may be improved during ERL through increased tidal volume as well as delayed expiratory lung emptying secondary to sustained PIA.