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Rationale: Several studies in mild chronic obstructive pulmonary disease (COPD) have shown a higher than normal ventilatory equivalent for carbon dioxide (e/co₂) during exercise. Our objective was to examine pulmonary gas exchange abnormalities and the mechanisms of high e/co₂ in mild COPD and its impact on dyspnea and exercise intolerance.

Methods: Twenty-two subjects (11 patients with GOLD [Global Initiative for Chronic Obstructive Lung Disease] grade 1B COPD, 11 age-matched healthy control subjects) undertook physiological testing and a symptom-limited incremental cycle exercise test with arterial blood gas collection.

Measurements and Main Results: Patients (post-bronchodilator FEV₁: 94 ± 10% predicted; mean ± SD) had evidence of peripheral airway dysfunction and reduced peak oxygen uptake compared with control subjects (80 ± 18 vs. 113 ± 24% predicted; P < 0.05). Arterial blood …