[Ventilatory response at maximal exercise in patients with chronic obstructive pulmonary disease].

OBJECTIVE: To 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. METHODS: Forty 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)]. RESULTS: The 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). CONCLUSION: Increased V(D)/V(T) may play an important role causing increase in EqCO(2) during exercise in patients with COPD.

[Measurement of alveolar-arterial partial pressure of oxygen difference in patients with chronic obstructive pulmonary disease both at rest and during maximal exercise].

OBJECTIVE: To investigate the change of alveolar-arterial partial pressure of oxygen (PO2) difference [P (A-a) O2)] at rest and during exercise in patients with chronic obstructive pulmonary disease (COPD). METHODS: Cardiopulmonary exercise testing was performed in 47 COPD male patients aged (66 +/- 8) at stable stage to measure the oxygen uptake (VO2) and carbon dioxide output (VCO2) continuously in a breath-by-breath mode. Arterial blood samples were drawn both at rest and during maximal exercise. P(A-a) O2 is computed by the equation: PAO2-PaO2. RESULTS: The PaO2 level during exercise was (89 +/- 14) mm Hg, a little bit, however, not significantly, lower than that at rest [(92 +/- 9) mm Hg, P = 0.506]. The PaCO2 during exercise was 43 +/- 3 mm Hg, significantly higher than that at rest (41 +/- 4 mm Hg, P = 0.003). The patients were divided into two groups according to lung diffusing capacity for carbon monoxide (DLco). There was a significant increase in P(A-a) O2 from (16 +/- 8) mm Hg at rest to (42 +/- 9) mm Hg during maximal exercise in the DLco < 80% group (P = 0.005); however, in the DLco >80% group the P(A-a) O2 level during maximal exercise was (26 +/- 6) mm Hg, not significantly different from that at rest [(20 +/- 6) mm Hg, P = 0.106]. The P(A-a)O2 level of the DLco <80% group during maximal exercise was (42 +/- 9) mm Hg, significantly higher than that at rest [(16 +/- 8) mm Hg, P = 0.005]. The P(A-a)O2 was significantly negatively correlated with the forced vital capacity (r= -0.581, P = 0.037) and DLco (r = -0.671, P = 0.012). CONCLUSION: The increase in P (A-a) O2 during exercise in the COPD patients is mainly due to the limited diffusing capacity of the lung.