• Qiu-Fen Xu, Hao-Yan Wang, Yao Xiao, Hai-Ju Ding, Jing Fan, and Ling Zhang.
• Department of Respiratory Medicine, Beijing Anzhen Hospital, Capital Medical University, Beijing 100029, China.
• Zhonghua Yi Xue Za Zhi. 2008 Aug 5;88(30):2108-11.

ObjectiveTo compare the difference in the ventilatory equivalent for carbon dioxide (EqCO(2)) between the patients with chronic obstructive pulmonary disease (COPD) and normal adults at maximal exercise, and to identify the factors inducing the abnormal change of EqCO(2) in COPD patients.MethodsForty male COPD patients and fifteen normal males underwent symptom-limited cardiopulmonary exercise testing. Oxygen uptake and carbon dioxide output were measured breath-by-breath. Arterial blood samples were collected at maximal exercise to undergo gas analysis so as to calculate the dead space/tidal volume ratios (V(D)/V(T)) and alveolar-arterial PO(2) difference [P((A-a))O(2)].ResultsThe maximal oxygen uptake, maximal carbon dioxide output, and arterial partial pressure of carbon dioxide (PaCO(2)) of the COPD patients were (14.8 +/- 3.6) ml x kg(-1) x min(-1), (19.4 +/- 5.9) ml x kg(-1) x min(-1), and (87.6 +/- 13.9) mm Hg respectively, all significantly lower than those of the normal controls [(18.9 +/- 4.2) ml x kg(-1) x min(-1), (25.3 +/- 7.1) ml x kg(-1) x min(-1), and (113.9 +/- 13.6) mm Hg respectively, all P < 0.01]; and the EqCO(2), PaCO(2), P((A-a))O(2), and V(D)/V(T) of the COPD patients at maximal exercise were 33.0 +/- 5.1, (43.5 +/- 3.1) mm Hg, (43.5 +/- 3.1) mm Hg, 0.33 +/- 0.12 respectively, all significantly higher than those of the normal controls [28.5 +/- 2.6, (39.6 +/- 4.9) mm Hg, (12.6 +/- 6.3) mm Hg, and 0.26 +/- 0.07 respectively, P < 0.01, P < 0.01, P < 0.01, P < 0.05]. Multiple regression analysis showed that EqCO(2) was significantly positively correlated with V(D)/V(T) at maximal exercise in the COPD patients (r = 0.57, P < 0.01).ConclusionIncreased V(D)/V(T) may play an important role causing increase in EqCO(2) during exercise in patients with COPD.

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