"Forward" and "backward" flow mechanisms of portal hypertension. Relative contributions in the rat model of portal vein stenosis.

The contribution of "forward" and "backward" flow mechanisms to the increased portal pressure observed in the rat model of portal vein stenosis was evaluated using experimental and theoretical data. The experimental data indicate that portal venous inflow, portasystemic shunting, and portal venous pressure are increased after 10 days of portal vein stenosis when compared with sham-operated controls. Furthermore, portal vascular resistance was 40% higher in portal hypertensive animals than in control animals. The elevated portal vascular resistance in the rat with portal vein stenosis was attributed to the high resistance of the portal venous collaterals. Incorporation of the experimental data into a mathematical model that simulated the changes induced by chronic portal vein stenosis allowed for fractionation of the "forward" and "backward" flow components involved in the pathogenesis of portal hypertension. Model predictions indicate that the "forward" and "backward" flow mechanisms account for 40% and 60% of the increase in portal pressure, respectively.