Relationship Between Oxygen Uptake and Oxygen Transport in Stable Patients with Chronic Obstructive Pulmonary Disease

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Abstract
This study was designed to determine whether alterations in systemic oxygen transport induced by the use of vasodilators for pulmonary hypertension would simultaneously affect oxygen uptake in patients with chronic obstructive pulmonary disease (COPD). Six stable patients with moderate to severe COPD were studied during resting conditons, nitroprusside infusion, a second control period, and after administration of hydralazine. Systemic oxygen transport fell with nitroprusside infusion (523 ± 94 to 418 ± 78 ml/min/m2, p < 0.05). With this there was a fall in oxygen uptake (135 ± 11 to 119 ± 12 ml/min/m2, p < 0.05), but only a minimal increase in oxygen extraction. In contrast, systemic oxygen transport was augmented in all patients when hydralazine was administered (444 ± 121 to 840 ± 157 ml/min/m2, p < 0.05). There was also a net increase in oxygen uptake in these patients (122 ± 19 to 148 ± 21 ml/min/m2, p < 0.05). We postulate that these clinically stable patients have a resting oxygen uptake that may become dependent on systemic oxygen transport whenever the latter decreases. This phenomenon has been described previously only in patients with adult respiratory distress syndrome, and it is important to consider when designing studies of pharmacologic therapy for COPD complicated by pulmonary hypertension.