AIMTo study the relationships between dyspnea and respiratory drive or respiratory muscle function in COPD.

METHODSThirty-one patients with COPD and 26 normal subjects were involved in the study. Routine pulmonary function, pulmonary diffusing capacity, P0.1, PI(max) were measured at rest. Oxygen consumption (VO2), carbon dioxide production (VCO2), minute ventilation (VE) etc were observed during exercise test. Dyspnea was assessed with Borg Scale (BS) simultaneously. Arterial blood gas measured before and after exercise.

RESULTS(1) PI(max) of COPD (5.33 +/- 1.95) kPa decreased compared with the normal subjects (7.02 +/- 2.53) kPa, P < 0.05, P0.1 of COPD (0.37 +/- 0.12) kPa increased compared with the normal subjects (0.26 +/- 0.09) kPa, P < 0.05, inspiratory drive efficacy (V(T)/P0.1) of COPD (1.6 +/- 0.31) L/kPa decreased than that of the normal subjects (2.1 +/- 0.53) L/kPa, P < 0.05. P0.1/PI(max) of COPD (0.069 +/- 0.021) was higher than that of the normal individuals (0.037 +/- 0.009), P < 0.01. (2) Peak exercise dyspnea was correlated with dyspnea at rest and P0.1/PI(max) (r = 0.41, P < 0.05 and r = 0.48, P < 0.05, respectively), and P0.1/PI(max) was also positively correlated with the change in BS from rest to maximal exercise (deltaBS) (r = 0.44, P < 0.05) in COPD patients.

CONCLUSIONIn COPD, breathlessness during exercise is not simply related to hyperinflation and the damaged gas exchange, but also to the relatively increased respiratory drive and dysfunction of respiratory muscle.