Acute hemodynamic effects of prostacyclin infusion

The hemodynamic effects of prostacyclin (PGI2) were studied in seven patients with severe or malignant hypertension. Blood pressure, cardiac output (Cardio-Green dilution method) and total blood volume (131/-Albumin dilution method) were measured before and during a PGI2 infusion, the effective dose ranging from 10 to 20 ng/kg/min. Cardiac index (C7) rose from 2-8 to 3-9 l/min/m2 and heart rate (HR) from 75 to 94 beats/min (P < 001). Mean blood pressure decreased from 154 to 120 mm Hg (P <0001) and total peripheral resistance from 4650 to 2540 dynes s cm~5 (P < 0001). The ratio: central blood volume/total blood volume increased from 0-21 to 0-26 (P < 0001). The decrease in blood pressure was related to the dose of prostacyclin (P < 0-001), but the vasodilatation was dose-dependent only from 5 to 12-5 ng\kg\min; for a higher dose, the decrease in blood pressure was related to the decrease in cardiac output as the heart rate was reduced. The results confirmed that PGI2 produces a potent vasodilatation of the arterial system; the decrease in blood pressure was limited by an increase in cardiac index mainly related to the tachycardia induced by prostacyclin; significant central translocation of blood suggested that PGI2 did not produce dilatation of the capacitance vessels. At low doses, the sympathetic nervous system was greatly stimulated by PGI2; at a higher dose, the vagal stimulation was predominant, inducing bradycardia and a fall in blood pressure. Since their discovery, prostaglandins have raise