Nonlinear resistances in the hepatic microcirculation.
Maass-Moreno, Roberto, and Carl F. Rothe.
Indiana University School of Medicine, Dept. of Physiology and
Biophysics, Med.Sci. 376, 635 Barnhill Dr., Indianapolis, IN
46202
APStracts 2:0266H, 1995.
The liver provides a reservoir available for mobilizing large amounts
of blood but, if a change in downstream (outflow) pressure below a
certain magnitude (break pressure) does not change upstream
pressures, then blood volume redistribution may be limited. For
downstream pressures larger than the break pressure, the upstream
pressures change proportionately. We tested the hypothesis that this
nonlinear mode of pressure transmission could be found both from the
abdominal vena cava to the hepatic microcirculation and from the
hepatic microcirculation to the portal vein. We measured
microvascular pressures at the liver surface of rabbits using a
servo-null micropipette technique. In 16 of 30 measurements,
increasing the pressure at the liver outflow, by partially occluding
the caudal thoracic vena cava, caused an increase in hepatic venular
pressure only after the abdominal vena cava pressure exceeded a break
pressure of 2.85 +/- 0.92 mmHg. In 13 of 31 measurements, portal
venous pressure was not changed until the hepatic venular pressure
exceeded a break pressure of 3.36 +/- 0.54 mmHg. Similar behavior and
values were obtained for sinusoids and portal venules. When present,
the sharp inflection in the upstream-vs-downstream pressure plots
suggest that this may be caused by a Starling-resistor type
mechanism. When the break was absent, the downstream pressure may
have been larger that the break pressure. We conclude that
significant hepatic resistances with nonlinear characteristics exist
both upstream and downstream to the central venules, sinusoids and
portal venules.
Received 6 February 1995; accepted in final form 12 June 1995.
APS Manuscript Number H111-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 11 July 1995.