Ventilatory cost of exercise in chronic obstructive pulmonary disease.

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Abstract
The O2 cost of increased ventilation was measured at rest and during exercise in 11 normal subjects and 17 patients with chronic obstructive pulmonary disease (COPD). The O2 cost of increased ventilation in normal subjects was 1.96 ml/liter of ventilation at rest and 4.2 ml/liter during exercise. In patients with COPD the O2 cost of increased ventilation was 6.3 ml/liter of ventilation at rest and 9.3 ml/liter during exercise. In normal subjects, the requirements of the respiratory muscles during exercise represented only a small proportion of the total O2 consumption, and therefore is probably not a factor in limiting exercise performance. In patients with COPD, on the other hand, there was a disproportionate increase in ventilation for a given mechanical work load and O2 consumption during exercise. As a result of this and the high O2 cost of increased ventilation, a large proportion of the total O2 consumption during exercise was utilized by the respiratory apparatus, leaving a decreased amount available for nonrespiratory muscles. The O2 cost of increased ventilation during exercise may be an important factor limiting the physical performance of patients with COPD.