The role of hydralazine therapy for pulmonary arterial hypertension of unknown cause.

Hydralazine was administered acutely to 12 patients who had pulmonary arterial hypertension of unknown cause. All of the patients were studied at rest and nine during exercise. On the basis of hydralazine response at rest, the patients were divided in two groups. In six patients (group A), pulmonary arteriolar resistance (Rp) decreased from 8.4 +/- 1.4 to 4.8 +/- 1.4 U/m2 (p less than 0.001), cardiac index (CI) increased from 3.47 +/- 0.3 to 5.86 +/- 0.5 1/min/m2 (p less than 0.005) and systemic resistance (Rs) decreased from 25 +/- 4 to 14 +/- 2 U/m2 (p less than 0.01). The Rp/Rs ratio did not change significantly after hydralazine (0.32 +/- 0.03 vs 0.33 +/- 0.07, NS). In the other six patients (group B), Rs decreased from 25 +/- 2 to 17.0 +/- 1 U/m2 (p less than 0.01), but the other variables did not change significantly. Our results suggest that the pulmonary vasodilatory effect of hydralazine caused a marked reduction in right ventricular afterload in group A. In group B, a marked systemic vasodilatory effect occurred and right ventricular afterload was not reduced. On the basis of the previous hemodynamic response, only group A patients were treated with oral hydralazine (50 mg every 6 hours). Hemodynamic measurements were repeated 48 hours after hydralazine, both at rest and during exercise, as well as 8 months later in five of the six patients in whom the beneficial hemodynamic effects persisted. These data suggest that hydralazine can reduce Rp in selected patients (pulmonary arterial pressure less than 60 mm Hg, Rp less than 15 U/m2 and Rp/Rs ratio less than 0.7) with pulmonary hypertension of unknown cause.