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Blunted maximum cardiac output and systemic O2 extraction could constitute primary limits to exercise in severe chronic obstructive pulmonary disease (COPD) or they could simply reflect cessation of exercise because of abnormal pulmonary mechanics. To determine which is the case, eight consecutive patients with severe COPD (FEV1 = 0. 56 +/- 0.04 L, mean +/- SEM), five of whom had alpha1-antiprotease deficiency, performed two incremental cycling tests while breathing N2-O2 or He-O2. Expired gases and V E were measured, and radial and pulmonary arterial blood was simultaneously sampled each minute. Peak exercise V E was higher with He-O2 than with N2-O2 (25.5 +/- 2. 2 versus 19.3 +/- 1.5 L/min, p = 0.002) and PaCO2 was lower (42 +/- 2 versus 46 +/- 2 mm Hg, p = 0.0003). V O2max improved only modestly (594 +/- 75 versus 514 +/- 54 ml/min, p = 0.04), and was accompanied by an increase in peak exercise CaO2 (18.7 +/- 0.9 versus 17.6 +/- 0. 9 ml/dl, p = 0.02). Peak Fick cardiac output was decreased (39 +/- 3% pred) and CvO2 was elevated (130 +/- 10% pred), and neither improved with He-O2 (p > 0.05 for each). Abnormal peak exercise cardiac output and systemic O2 extraction in severe COPD cannot be fully accounted for by limiting pulmonary mechanics and may contribute to exercise intolerance.

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