Journal of Applied Physiology, Vol 51, Issue 6 1574-1580, Copyright © 1981 by American Physiological Society
Deficiencies in pore-membrane models of microvascular fluid and solute transudation
R. Winn, B. Nadir, J. Gleisner, J. Stothert and J. Hildebrandt
We have attempted to determine the membrane parameters,
permeability-surface area product (PS) and reflection coefficient (sigma),
necessary to describe solute exchange in the pulmonary circulation.
Experimental lymph-to-plasma ratios were obtained for total protein (Rtot)
and albumin (Ralb) using lung lymph collected from goats with chronic lung
lymph fistulae. Lymph flow (QL) and solute flow (QS) were varied by
increasing microvascular pressure in a stepwise manner by inflating a
balloon in the left atrium. The increased QL and decreased Ralb from
multiple experiments in four goats were used to plot PS vs. sigma using the
equation of Patlak et al. (J. Theor. Biol. 5: 426-442, 1963). The region of
intersection of two or more such curves should identify the two membrane
constants. However, these curves rarely intersected suggesting that perhaps
the lung barrier was not adequately represented by a single homoporous
membrane. To evaluate heteroporosity, the three-pore model of Blake and
Staub (Microvasc. Res. 12: 197-220, 1976) was investigated. By use of their
pore sizes and relative pore distributions, values for the fluid filtration
coefficient, PS, and sigma of each pore type were calculated, and finally
QL and R were predicted at various microvascular pressures. When these
calculated values of QL and R were plotted using the equation of Patlak et
al., an equivalent homoporous PS and sigma could still be found. Therefore,
a heteroporous membrane does not appear to explain the failure of our data
plots to intersect. Possible alternative models are suggested.
