QUANTITATIVE EFFECTS OF SODIUM-NITROPRUSSIDE ON CORONARY HEMODYNAMICS AND LEFT-VENTRICULAR FUNCTION IN DOGS

The authors studied the effects of nitroprusside on left ventricular contractility, coronary blood flow, and coronary vascular resistance in dogs during right heart bypass in which stroke volume, aortic pressure, and heart rate were controlled. Intravenous nitroprusside increased coronary blood flow and decreased coronary vascular resistance but did not change left ventricular end-diastolic pressure or maximum dP/dt when aortic pressure was held constant. When aortic pressure was allowed to fall during intravenous nitroprusside infusion, coronary flow increased slightly as coronary resistance decreased, but left ventricular contractility increased (left ventricular end-diastolic pressure fell at constant maximum dP/dt). After β-adrenergic blockade, intravenous nitroprusside decreased maximum dP/dt, coronary flow, and coronary resistance when aortic pressure fell during intravenous nitroprusside infusion. When the coronary and systemic circulations were separated and coronary pressure was kept constant, intravenous nitroprusside did not change coronary flow or coronary resistance, but maximum dP/dt decreased when aortic pressure fell. Conversely, intracoronary nitroprusside increased coronary flow and decreased coronary resistance but did not change left ventricular end-diastolic pressure or maximum dP/dt. We conclude that nitroprusside dilates coronary arteries but has no direct effect on left ventricular contractility. When mean aortic pressure is decreased by nitroprusside, β-adrenergic stimulation results in increased left ventricular contractility and indirect coronary dilation.