ARTERIAL BLOOD-GAS TENSION CHANGES AT THE START OF EXERCISE IN CHRONIC OBSTRUCTIVE PULMONARY-DISEASE

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Abstract
In a previously reported study of normal subjects, large decreases in arterial O2 tension (PaO2) of as much as 37 mm Hg were measured during the first 90 s of slow stair-climbing exercise (chosen as a common daily exertion). The changes in PaO2, arterial CO2 tension (PaCO2) and ventilation in 7 patients with chronic obstructive pulmonary disease and resting hypoxemia during the first 90 s of similar exercise were reported. The patient group showed significantly smaller unsteady-state decreases in PaO2 starting from a smaller resting value (patient group, 72 .+-. 2.6 mm Hg, mean .+-. SE; normal group, 92 .+-. 2.0 mm Hg; P < 0.001) and decreasing to a similar smallest value (patient group, 58 .+-. 3.8 mm Hg; normal group, 65 .+-. 3.4 mm Hg; P > 0.05). PaCO2 tended to oscillate around the resting value in both the patient group and the normal group, and the rates of increase in ventilation in the 2 groups were similar. The physiologic processes that could limit the unsteady-state decrease in PaO2 in the patient group are analyzed, the analysis suggesting that a slower rate of increase in tissue consumption of O2 is most likely to account for the smaller decrease in PaO2.

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