Effect of nifedipine on splanchnic and pulmonary vascular capacitance

This study examines the hypothesis that nifedipine may increase splanchnic vascular capacitance and thus change the distribution of blood between the splanchnic and pulmonary circulation in heart failure patients. Relative regional blood volumes were determined by equilibrium blood pool scintigraphy during a 10 min baseline period and for 30 min after nifedipine 20 mg sublingually, with simultaneous recordings of systemic and pulmonary arterial pressures, hepatic venous wedge pressure, and cardiac output. Eight patients with ischaemic heart failure received nifedipine. Four patients served as controls. Nifedipine reduced mean arterial pressure and systemic vascular resistance in every patient. 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 splanchnic vascular pressure-volume relationship. Nifedipine caused a 6.3 +/- 1.0% increase in relative pulmonary blood volume and a slight increase 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 blood 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 increased distending pressure.