Journal of Applied Physiology, Vol 56, Issue 5 1389-1402, Copyright © 1984 by American Physiological Society
A model of unsteady-state transvascular fluid and protein transport in the lung
R. J. Roselli, R. E. Parker and T. R. Harris
Models of steady-state fluid and solute transport in the microcirculation
are used primarily to characterize filtration and permeability properties
of the transport barrier. Important transient relationships, such as the
rate of fluid accumulation in the tissue, cannot be predicted with
steady-state models. In this paper we present three simple models of
unsteady-state fluid and protein exchange between blood plasma and
interstitial fluid. The first treats the interstitium as a homogeneous
well-mixed compliant compartment, the second includes an interstitial gel,
and the third allows for both gel and free fluid in the interstitium.
Because we are primarily interested in lung transvascular exchange we used
the multiple-pore model and pore sizes described by Harris and Roselli (J.
Appl. Physiol.: Respirat . Environ. Exercise Physiol. 50: 1-14, 1981) to
characterize the microvascular barrier. However, the unsteady-state
transport theory presented here should apply to other organ systems and can
be used with different conceptual models of the blood-lymph barrier. For a
step increase in microvascular pressure we found good agreement between
theoretical and experimental lymph flow and lymph concentrations in the
sheep lung when the following parameter ranges were used: base-line
interstitial volume, 150-190 ml; interstitial compliance, 7-10 ml/Torr;
initial interstitial fluid pressure, -1 Torr; pressure in initial
lymphatics, -5 to -6 Torr; and conductivity of the interstitium and
lymphatic barrier, 4.25 X 10(-4) ml X s-1 X Torr-1. Based on these values
the model predicts 50% of the total change in interstitial water volume
occurs in the first 45 min after a step change in microvascular
pressure.(ABSTRACT TRUNCATED AT 250 WORDS)
