The interaction of extravascular pressure fields and fluid exchange in capillary networks

A previously developed model [4] is extended to include capillary networks of realistic three-dimensional architecture, and used to examine the interaction of the local tissue pressure field with fluid exchange. Fluid-flux calculations using this model show that interaction, which reduces the predicted amount of fluid exchanged below that predicted by the classical Starling's hypothesis, increases with increasing numbers of capillary segments. Fluid filtration from one capillary is affected by the local pressure fields of other capillaries, resulting in a capillary-capillary interaction. This interaction increases with increasing values of the ratio of endothelial to tissue hydraulic conductivities. For large values of the ratio, the model predicts a fluid flux almost 90% less than that calculated by Starling's hypothesis. It is shown, however, that at even the smallest physiologically reasonable value of this ratio, interaction still has a significant effect in reducing the predicted fluid exchange in large networks.