Effects of oral hydralazine on gas exchange in patients with cor pulmonale

Vasodilators lower total pulmonary vascular resistance in some patients with pulmonary hypertension, but if vasodilators worsen arterial oxygenation in cor pulmonale, as they do in some patients with left ventricular failure, the benefits of a decrease in vascular resistance would be offset by a lack of change or a deterioration in systemic oxygen delivery. Measurement was made of arterial and mixed venous blood gases, minute ventilation, shunt fraction, alveolar-arterial oxygen difference, pulmonary arterial pressures, and cardiac output before and four hours after a single dose of hydralazine, 75 mg orally, in six patients (Group I) and before and after 48 hours of hydralazine, 50 to 75 mg orally, every six hours in 10 patients (Group II). Cardiac output increased 36 percent in Group I and 48 percent in Group II. In both groups total pulmonary vascular resistance decreased (8.0 +/- 2.8 to 6.1 +/- 2.6 units in Group I, p less than 0.01; 9.7 +/- 3.7 to 5.6 +/- 2.1 units in Group II, p less than 0.01). Arterial PO2 increased significantly both in Group I (61 +/- 8 to 67 +/- 10 torr, p less than 0.05) and Group II (50 +/- 13 to 54 +/- 13, p less than 0.05); however shunt fraction and alveolar-arterial oxygen difference were unchanged. The ratio of dead space to tidal volume decreased slightly in both groups, and minute ventilation increased significantly. Systemic oxygen delivery was increased by 39 and 51 percent in Groups I and II, respectively. Thus, gas exchange may be preserved or improved when hydralazine is used in the treatment of cor pulmonale.