AJP - Heart and Circulatory Physiology, Vol 266, Issue 6 2268-H2278, Copyright © 1994 by American Physiological Society
Blood volume redistribution from a passive elastic permeable microcirculation due to hypovolemia
A. J. LaForte, L. P. Lee, G. F. Rich, T. C. Skalak and J. S. Lee
Department of Biomedical Engineering, University of Virginia, Charlottesville 22908.
We measured the variations in blood and plasma density for a cyclic
hemorrhage protocol in conscious rabbits to calculate delta Vf [the volume
of fluid restituted into the circulation from the time the blood volume was
at its control to that after the hemorrhage of a blood volume (delta V)]
and delta Vs (the volume shift from micro- to macrocirculation over the
same time interval). We found that delta Vf is 7% of delta V and delta Vs
60% of delta V. They combine to reduce the effect of hemorrhage on
macrovascular volume by 67% of delta V. Based on a two-resistor circulation
model, the change in microcirculatory pressure (delta Pmic) from control to
hemorrhage was estimated from the measured cardiac outputs and arterial and
venous pressures. The computations indicate that delta Vs (or delta Vf) is
linearly related to delta Pmic. With one relation fitting all data of
rabbits that were conscious, infused with hexamethonium, and anesthetized
with pentobarbital sodium, we concluded that the two short-term volume
redistributions are not direct neural control or local regulation, but the
response of a passive, permeable microcirculation to delta Pmic. From the
linear relations, we obtained 0.88 ml.mmHg-1.kg-1 as the compliance of the
rabbit microcirculation and 0.21 ml.min-1.mmHg-1.kg-1 as its filtration
coefficient.
