Hemodynamic characteristics of the intrahepatic portal vascular bed over an extended flow range: a study in the isolated perfused rat liver.

The relationship between the perfusion pressure (P) and resistance (R) of the intrahepatic portal vascular bed was determined in isolated rat liver preparations perfused with fresh, heparinized rat blood (hematocrit 30%), with rat blood containing a vasodilator agent (sodium nitroprusside, 1 X 10(-3) mol/L), or with 2.5% bovine serum albumin in Krebs-Henseleit buffer (BSA-KH). Pressure-flow curves were constructed over an extended range of portal venous inflow (0 to 70 mL.min-1, corresponding to a flow rate per gram liver wet weight, Q, of approximately 0 to 7 mL.min-1.g-1). Subsequent analysis showed that two mathematical expressions adequately described the data over the full range of flow. Thus, the pressure-flow curve could be represented by (a) the sum of a linear plus a hyperbolic function, i.e., P = Q.R' + Pmax.Q/(Q + Km), where R', Pmax, and Km are constants, or (b) by the simple equation G = C.P, where G is the conductance (Q/P), and C is a conductivity constant. The values of R', Pmax, Km, and C were significantly different under each of the circumstances investigated, but the form of the curve was not altered. Hence, it is proposed that these parameters can be used to describe the fundamental hemodynamic properties of the portal vascular bed of the isolated rat liver. The results are discussed in terms of the microvascular recruitment and distensible resistance vessel models of the hepatic microcirculation.