Pressure-flow analysis of portal vein and hepatic artery interactions in porcine liver.

Interactions between the hepatic arterial and portal venous circulations were investigated in nine intact and eight isolated perfused porcine livers. Pressure-flow (P-Q) relationships were obtained in either the portal vein or hepatic artery with constant baseline or low flow in the other bed and a stable hepatic venous pressure (Phv). The slope was obtained by linear regression analysis of the P-Q relationship, and effective back pressure (Pback) was obtained from the pressure intercept for the portal vein and the measured zero-flow pressure for the hepatic artery. The Pback in the hepatic artery (13.4 +/- 1.5 mmHg) and the portal vein (4.6 +/- 0.3 mmHg) were higher than Phv (P < 0.05). Reducing portal vein flow (Qpv) produced an increase in hepatic artery flow (Qha) (P < 0.05) due only to a decrease in slope (P < 0.05). Decreasing Qha caused an identical change in Pback of the portal vein (P < 0.05) in the intact and isolated liver preparations. A change in Qpv alters the hepatic arterial resistance upstream from the site of a constant arterial Pback. Changes in total flow through the common sinusoidal compartment appear to alter the Pback of the portal vein via hydraulic mechanisms.