Efficacy of vasodilator therapy in canine model of acute pulmonary hypertension.

This study was performed to determine 1) the effects of acute pulmonary embolization (induced by injection of autologous muscle) on right ventricular (RV) performance, coronary hemodynamics, and gas exchange; and 2) the efficacy of subsequent administration of nitroglycerin, prostaglandin E1, and hydralazine with regard to improvement in RV function and gas exchange in eight open-chest dogs. After embolization, pulmonary artery (PA) pressure and vascular resistance (PVR) increased three- to fivefold without changes in RV end-diastolic dimensions (ultrasonic dimension technique) or pressure. However, systolic dimensions increased, and stroke volume (SV) fell. Gas exchange, lung compliance, and pH worsened. Subsequent administration of nitroglycerin (5 micrograms.kg-1.min-1) and prostaglandin E1 (0.2 micrograms.kg-1.min-1) caused further decreases in SV and pH. In contrast, hydralazine (mean 0.15 mg/kg) improved myocardial segment shortening, SV, PVR, pulmonary artery flow, and gas exchange. Coronary blood flow increased by 110%. Thus in this canine model of combined pulmonary hypertension and respiratory insufficiency, nitroglycerin and prostaglandin E1 exerted no beneficial cardiopulmonary effects. In contrast, hydralazine improved regional and global RV performance and gas exchange.