[Exercise tolerance in relation to ventilatory drive and respiratory muscle function in COPD].

OBJECTIVE

To assess the relationships between exercise tolerance and respiratory drive and respiratory muscle function in COPD.

METHODS

28 patients with COPD and 26 normal subjects were involved in the study. Routine pulmonary function, pulmonary diffusing capacity, P0.1, PImax were measured at rest. Oxygen consumption (VO2), carbon dioxide production (VCO2), minute ventilation (VE) etc were measured during exercise testing. Borg Scale was recorded simultaneously. Arterial blood gases were measured before and after exercise.

RESULTS

(1) PImax in COPD group (40 +/- 15 mm Hg) was significantly lower than that in the normal group [(53 +/- 19) mm Hg, P < 0.05]. P0.1 in COPD group [(2.8 +/- 0.9) mm Hg] was significantly higher than that in the normal group [(2.0 +/- 0.7) mm Hg, P < 0.05]. Inspiratory drive efficacy (VT/P0.1) in COPD group [(0.21 +/- 0.04) L/mm Hg] was significantly lower than that in the normal group [(0.28 +/- 0.07) L/mm Hg, P < 0.05]. P0.1/PImax in COPD group was (0.069 +/- 0.021), significantly higher than that in the normal group [(0.037 +/- 0.009), P < 0.01]. (2) VO2max was correlated with P0.1/Pimax and Borg Scale in COPD patients (r = 0.66, P < 0.01, and r = 0.53, P < 0.05 respectively). Borg Scale was also positively correlated with P0.1/PImax in COPD group (r = 0.49, P < 0.05).

CONCLUSION

In addition to airway obstruction and the damaged gas exchange, exercise intolerance in COPD may also be related to the increased respiratory drive and dysfunction of respiratory muscle.