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

Abstract

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.

The effect of hepatocyte enlargement on the hemodynamic characteristics of the isolated perfused rat liver preparation

“…16 Regression analysis of this high-flow data was used to derive the zero-flow intercept, P 0 , as well as the gradient RЈ. It has also been shown previously that the reciprocal of RЈ provides an estimate of the maximal portal vascular conductance, G max .…”

“…It has also been shown previously that the reciprocal of RЈ provides an estimate of the maximal portal vascular conductance, G max . 16 …”

“…16,[18][19][20][21][22][23][24][25] At high-flow rates, the pressure-flow curves become linear, 16,19 a phenomenon which might be caused by either the microvascular bed becoming fully recruited, the vessels becoming relatively rigid as tissue elements become fully stretched, or a combination of both. 16,[18][19]24 That curve has a positive P 0 and has been described as a ''passive'' type pressure-flow curve. 24,26 The relative importance of vascular recruitment versus distension to the hepatic portal pressure-flow curve remains a matter of debate; however, it is possible to apply an empirical approach to the analysis of data obtained from the IPRL.…”

“…15 The liver was then isolated and perfused as described in detail in a previous paper. 16 Briefly, the portal vein was cannulated, and the liver was flushed with oxygenated buffer as it was rapidly excised. The preparation was then transferred to a temperature-controlled cabinet (37 Ϯ 0.5°C) and perfused via the portal vein with BSA-KH oxygenated with carbogen gas (95% O 2 , 5% CO 2 ).…”

“…Pressure-flow curves were subsequently constructed by adjusting the flow rate to 70 mL/min then by reducing the flow in steps to 1 mL/min. 16 At the end of the experiment, the liver was removed, blotted dry and weighed, and the flow rates were subsequently calculated as mL/min/g.…”