Pharmacological vs. mechanical reduction in portal pressure: a comparative study.

Previous studies have shown that decreasing blood flow in the superior mesenteric artery (SMA) by the infusion of intra-arterial vasopressin into or partial mechanical obstruction of the SMA by a balloon catheter (partial balloon obstruction) causes similar alterations in splanchnic hemodynamics, but divergent changes in systemic hemodynamics. The effects of these two methods of reducing SMA blood flow were compared in each of six anesthetized normal dogs. Vasopressin and partial balloon obstruction induce similar reductions in portal pressure (-54 +/- 12% vs. -46 +/- 11%), wedge hepatic vein pressure (-54 +/- 13% vs. -53 +/- 18%), and portal venous flow (-34 +/- 7% vs. -37 +/- 7%). Significantly different effects between intra-arterial vasopressin and partial balloon obstruction were observed, however, in cardiac output (a decrease of -24 +/- 5% vs. an increase of +12 +/- 4%) (P less than 0.001), heart rate (-8 +/- 3% vs. 0) (P less than 0.05), and systemic vascular resistance (+36 +/- 8% vs. -2 +/- 2%) (P less than 0.005), respectively. These results indicate that the two procedures are equally effective in reducing portal venous pressure and blood flow. Partial balloon obstruction, however, does not induce the potentially deleterious systemic hemodynamic effects seen with vasopressin infusion. In fact, some of the changes observed with partial balloon obstruction, especially the increase in cardiac output, are considered to be beneficial. In an additional five dogs, partial balloon obstruction was maintained for 5 hours. Throughout, the reduction in portal venous pressure (hepatic venous wedge minus hepatic venous free pressure) was maintained at less than half of the baseline levels (4.75 +/- 0.43 vs. 2.25 +/- 0.32 mm Hg), and the mean arterial pressure at baseline values. All of the dogs survived and were well at 1 week after the prolonged partial obstruction. No abnormalities were observed in the anatomical or histological studies of the small intestine. This study suggests that partial balloon obstruction of the SMA has theoretical therapeutic advantages over intra-arterial vasopressin for reducing portal venous pressure.