American Review of Respiratory Disease

Oxygen (O2) has been reported to improve exercise tolerance in some patients with chronic obstructive pulmonary disease (COPD) despite only mild resting hypoxemia (PaO2 > 60 mm Hg). To confirm these prior studies and evaluate potential mechanisms of benefit, we measured dyspnea scores by numeric rating scale during cycle ergometry endurance testing and correlated the severity of dyspnea with right ventricular systolic pressure (RVSP) measured by Doppler echocardiography during a separate supine incremental exercise test. Both sets of exercise were performed according to a randomized double-blind crossover protocol in which patients breathed compressed air or 40% O2. We studied 12 patients with severe COPD (FEV1 0.89 ± 0.09 L [mean ± SEM], FEV1/FVC 37 ± 2%, DlCO 9.8 ± 1.5 ml/min/mm Hg [47% of predicted], PaO2 71 ± 2.6 mm Hg). With endurance testing on compressed air, PaO2 did not change significantly in the group as whole (postexercise PaO2 63 ± 5.1 mm Hg, p = NS), but did fall to less than 55 mm Hg in four patients from this group. Duration of exercise increased on 40% O2 from 10.3 ± 1.6 to 14.2 ± 1.5 min (p = 0.005), and the rise in dyspnea scores was delayed. Oxygen delayed the rise in RVSP with incremental exercise in all patients and lowered the mean RVSP at maximum exercise from 71 ± 8 to 64 ± 7 mm Hg (p < 0.03). Improvement in duration of exercise correlated with decrease in dyspnea (r2 = 0.66, p = 0.001) but not with decreases in heart rate, minute ventilation, or RVSP. Four patients more than doubled their duration of exercise on 40% O2, but only two of these four desaturated while exercising on compressed air. We conclude that supplemental O2 improves dyspnea and exercise tolerance in patients with COPD who have only mild hypoxemia at rest, and that the Improvement may be dramatic even in the absence of exercise-induced oxyhemoglobin desaturatlon.

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