Prazosin and hydralazine in congestive heart failure. Regional hemodynamic effects in relation to dose.

Central hemodynamic variables and regional blood flow and vascular resistances were ascertained in patients with severe congestive heart failure before and after the oral administration of prazosin hydrochloride or hydralazine. Prazosin was administered in doses of 2, 5, and 10 mg and hydralazine, 75 and 100 mg. Although both agents significantly increased cardiac output and decreased vascular resistances, their effects on regional blood flow and vascular resistances were considerably different. Prazosin increased hepatic blood flow and reduced hepatic vascular resistance at lower doses; these changes decreased as prazosin was increased. Hydralazine did not significantly alter mean hepatic blood flow or vascular resistance. Prazosin did not affect renal blood flow or renal vascular resistance. In contrast, hydralazine significantly increased renal blood flow and reduced vascular resistance; the changes were dose related. Both drugs augmented limb blood flow and diminished limb vascular resistance; the magnitude of change was dose dependent.