Effect of variable hydraulic conductivity on transcapillary fluid exchange: Application to the microcirculation of rat intestinal muscle

A theoretical model has been developed to study the influence of variable hydraulic wall conductivity of single capillaries on transmural fluid exchange. A systematic study has been carried out to examine the factors which determine the direction of transcapillary fluid flow; i.e., filtration or absorption. One important result of this study is that, in addition to capillary pressure and plasma protein concentration, the shape of the axial distribution of the hydraulic conductivity of the capillary wall can affect the direction of transmural fluid movement. The experimental data for the axial distribution of the hydraulic conductivity of single capillaries in the rat intestinal muscle of R. W. Gore, W. Schoknecht, and H. G. Bohlen (In “Microcirculation,” J. Grayson and W. Zingg, eds., Vol. 1, pp. 331–332, Plenum, New York) were employed in the present model in order to predict axial and radial fluid flow. The comparison of the results with experimental data for capillary pressure and transmural flux at four axial positions showed excellent agreement. The results of the present model support the experimental finding of Gore et al. that the capillary bed in the rat intestinal muscle is absorptive.