The role of pulmonary stretch receptor activation during cough in dogs.

The role of pulmonary stretch receptors in the modulation of expiratory muscle activity during cough is controversial. To evaluate their potential influence on expiratory effort during cough, we compared expiratory muscle activity during unobstructed cough to that during obstructed cough in which the trachea was occluded at the end-inspiration and maintained throughout the subsequent expiration. Cough was evoked by mechanical stimulation of the intrathoracic trachea in 9 anesthetized, tracheotomized dogs. Peak triangularis sterni (TS), internal intercostal (IIC) and transversus abdominis (TA) muscle EMG were monitored to assess both rib cage and abdominal muscle activation during expiration. During cough, expiratory activity increased and peak activity shifted from Stage II to Stage I expiration. Peak expiratory muscle activation during unobstructed and occluded coughs were not significantly different: during unobstructed coughs, peak EMG's (mean +/- SE as percent of resting breathing) were TS, 212 +/- 18; IIC, 425 +/- 72; TA, 406 +/- 66; and during obstructed cough: TS, 188 +/- 24; IIC, 365 +/- 44; TA, 387 +/- 77 (n = 9). These data indicate that enhanced vagal stimulation resulting from airway occlusion does not affect expiratory activity during cough. We suggest that during cough, the expiratory muscles are activated in a stereotypical pattern by the neural network generating the cough and this pattern of activation is not affected by phasic vagal input.