Hepatic outflow resistance, sinusoid pressure, and the vascular waterfall.

MITZNER, WAYNE. Hepatic outJrow resistance, sinusoid pressure, and the vascular waterfall. Am. J. Physiol. 227(3): 513-519. 1974.The pressure-flow characteristics of the hepatic common outflow resistance were determined in five anesthetized dogs. These curves were shown to be nearly linear in the range of normal flows, but exhibited a moderate convexity toward the pressure axis at low flows. The estimated sinusoid pressure at zero hepatic flow was found to be higher than the outflow (hepatic venous) pressure. This “closing pressure” averaged 1.6 mmHg relative to the hepatic venous pressure. Because of this closing pressure, estimated hepatic sinusoid pressure was only slightly less than the portal pressure. For an average portal venous pressure of 7 mmHg, hepatic venous pressure of 1.6 mmHg, and portal venous and hepatic arterial flows of 16.4 and 12.6 ml/min-kg body wt, respectively, sinusoid pressure was estimated to be 6.1 mmHg. The significance of a closing pressure in the hepatic outflow tract and the interpretation of outflow resistance in light of this closing pressure are discussed in detail. Two possible models of the hepatic vasculature are presented.