Effects of hydralazine and nitroprusside on cardiopulmonary function when a decrease in cardiac output complicates a short-term increase in pulmonary vascular resistance

Abstract

We investigated the short-term cardiopulmonary effects of nitroprusside and hydralazine when cardiac output (CO) was reduced by a short-term increase in pulmonary vascular resistance (PVR). In 6 anesthetized, ventilated dogs, small autologous blood clots, injected over 1 to 2 hr, increased right ventricular afterload. When CO had fallen approximately 40%, dogs were treated with nitroprusside and subsequently with hydralazine. Both drugs reduced biventricular filling pressures (p < .05), but only hydralazine increased CO and stroke volume (p < .05). Although mean blood pressure and pulmonary artery pressure remained constant with hydralazine, systemic vascular resistance and PVR decreased (p < .01). In contrast, although nitroprusside reduced blood pressure and systemic vascular resistance (p < .01), it did not affect PVR and pulmonary artery pressure. When CO is significantly reduced because of a short-term increase in PVR, hydralazine may be superior to nitroprusside in improving cardiopulmonary function.