[Effect of gas exchange at maximal intensity on exercise capacity in patients with chronic obstructive pulmonary disease].

Objective: To investigate the effect of gas exchange at maximal intensity on exercise capacity in patients with chronic obstructive pulmonary disease (COPD).

Methods: Forty-two male patients with COPD and 26 normal subjects performed incremental exercise test on cycle ergometer. Oxygen uptake and carbon dioxide output were measured continuously on the breath-by-breath mode. Arterial blood samples were drawn at maximal exercise. PaO2, PaCO2, the actual dead space/tidal volume ratios (V(D)/V(T)) and the alveolar-arterial PaO2 difference [ P(A-a) O2 ] were measured and calculated. Comparisons between the two groups were performed using independent samples t test. Linear regression analyses were made between maximal oxygen uptake (VO2max) and blood gas variables.

Results: VO2max in patients with COPD [(16 +/- 4) ml kg(-1) min(-1)] was significantly lower than in normal subjects [(19 +/- 6) ml kg(-1) min(-1)]. P(A-a)O2, V(D)/V(T) and PaCO2 were greater in patients [(43 +/- 3) mm Hg, 1 mm Hg =0.133 kPa, 0.35 +/- 0.11, (33 +/- 11) mm Hg] than in normal subjects at peak exercise [(40 +/- 5) mm Hg, 0.27 +/- 0.08, (15 +/- 7) mm Hg]. VO2max correlated strongly with V(D)/V(T) at peak exercise in patients (r = -0.734, P < 0.01).

Conclusion: The increase in V(D)/V(T) inducing ventilatory inefficiency during exercise is one of the important causes for decreased exercise capacity in patients with COPD.