Oral hydralazine therapy for primary pulmonary hypertension.

To evaluate the hemodynamic effects of hydralazine in four patients with primary pulmonary hypertension, we catheterized the right side of the heart before and 48 hours after starting therapy with oral hydralazine, 50 mg every six hours. Data were obtained at rest in four patients and also during exercise in three. After hydralazine, total pulmonary resistance at rest fell from 17.5 to 7.7 U, and pulmonary arteriolar resistance from 15.6 to 7.1 U; cardiac output increased from 3.8 to 7.1 liters per minute, and the arteriovenous oxygen difference narrowed from 7.8 to 5.4 ml per deciliter. Mean pulmonary and systemic arterial pressures were unchanged. Hydralazine also caused total pulmonary resistance during exercise to fall from 15.7 to 10.2 U, and cardiac output to rise from 4.7 to 7.0 liters per minute. Treatment was continued, and on repeat catheterizations three to six months later the hemodynamic effects persisted. These data suggest that hydralazine can reduce pulmonary resistance in some patients with idiopathic pulmonary hypertension.