EFFECT OF NIFEDIPINE ON SPLANCHNIC AND PULMONARY VASCULAR CAPACITANCE

This study examines the hypothesis that nifedipine may increase splanc hnic vascular capacitance and thus change the distribution of blood be tween the splanchnic and pulmonary circulation in heart failure patien ts. Relative regional blood volumes were determined by equilibrium blo od pool scintigraphy during a 10 min baseline period and for 30 min af ter nifedipine 20 mg sublingually, with simultaneous recordings of sys temic and pulmonary arterial pressures, hepatic venous wedge pressure, and cardiac output. Eight patients with ischaemic heart failure recei ved nifedipine. Four patients served as controls. Nifedipine reduced m ean arterial pressure and systemic vascular resistance in every patien t. There were no significant changes in the relative blood volumes of the intestinal, hepatic, or splenic regions or in hepatic venous wedge pressure (reflecting portal venous pressure), suggesting unchanged sp lanchnic vascular pressure-volume relationship. Nifedipine caused a 6. 3+/-1.0% increase in relative pulmonary blood volume and a slight incr ease in pulmonary vascular distending pressure from 16.1+/-2.9 mmHg to 17.5+/-2.8 mmHg (P<0.05), suggesting that the increase in pulmonary b lood volume was passively mediated. In conclusion, nifedipine did not change splanchnic vascular capacitance, but caused a small increase in pulmonary blood volume, which probably was a passive response to incr eased distending pressure.