Independence of Oxygen Consumption and Systemic Oxygen Transport in Patients with Either Stable Pulmonary Hypertension or Refractory Left Ventricular Failure

Recent studies have suggested that oxygen consumption (VO2) may be dependent on systemic oxygen transport (SOT) in patients with the adult respiratory distress syndrome. To evaluate this relationship in patients with chronically impaired SOT, 2 groups underwent control right heart catheterization. Twenty-six patients with pulmonary hypertension (Group I) were then reevaluated after 48 h of treatment with a vasodilator, either hydralazine or nifedipine. Nine patients with refractory left ventricular failure (Group II) were first studied using nitroprusside, and 24 h later were begun on a double-blind drug protocol using either minoxidil or hydralazine. A significant correlation existed between control SOT and VO2 in both groups (r = 0.65, p less than 0.001). There were no changes in either group, however, in VO2 with vasodilator therapy, despite significant increases in cardiac output and SOT. We conclude that although resting oxygen consumption may be correlated with systemic oxygen transport when SOT is at low levels in stable patients with chronically impaired SOT, VO2 appears to be independent of SOT when oxygen delivery is increased by the administration of vasodilators.