Does expiratory muscle activity influence dynamic hyperinflation and exertional dyspnea in COPD?

Increased expiratory muscle activity is common during exercise in patients with COPD but its role in modulating operating lung volumes and dyspnea during incremental cycle ergometry is currently unknown. We compared gastric (Pga) and esophageal (Pes) pressures, operating lung volumes and qualitative descriptors of dyspnea during exercise in 12 COPD patients and 12 age- and sex-matched healthy controls. Pes- and Pga-derived measures of expiratory muscle activity were significantly (p<0.05) greater in COPD than in health during exercise. End-expiratory lung volume (EELV) increased by 0.8L, independent of increased expiratory muscle activity in COPD. Dynamic function of the diaphragm was not different in health and COPD throughout exercise. In both groups, dyspnea descriptors alluding to increased work and inspiratory difficulty predominated whereas expiratory difficulty was rarely reported, even at the limits of tolerance. In conclusion, increased expiratory muscle activity did not mitigate the rise in EELV, the relatively early respiratory mechanical constraints or the attendant perceived inspiratory difficulty during exercise in COPD.