AJP - Regulatory, Integrative and Comparative Physiology, Vol 242, Issue 3 227-R236, Copyright © 1982 by American Physiological Society
Estimation of whole-body capillary transport parameters from osmotic transient data
M. B. Wolf
A mathematical model has been developed of short-term, extrarenal,
whole-body fluid volume regulation. The Kedem and Katchalsky equations are
used to describe rapid movements of crystalloid and colloid solutes and
water between five fluid compartments. Simulation results showing rapid
cell volume changes following a hyperosmotic crystalloid infusion
demonstrated the necessity of considering the effect of cellular water
shifts in osmotic transient experiments. From measurements of plasma volume
and osmolality in acutely nephrectomized dogs subjected to isosmotic and
hyperosmotic NaCl infusions and with the model, six parameters related to
capillary membrane transport of water and NaCl were estimated. The mean
capillary filtration capacity from six experiments was estimated as 0.01
ml.min-1.mmHg-1.100 g-1 of dog. This increased about threefold due to the
hyperosmolality. Mean values of capillary diffusion capacity and osmotic
reflection coefficient for NaCl were 0.37 cm3.s-1.100 g-1 and 0.087,
respectively. These results support the use of the osmotic transient
approach and a mathematical model to study the role of microvascular
transport in whole-body fluid volume regulation.
