Effect of extravascular pressure gradients on capillary fluid exchange

A mathematical model is developed to examine the effect of pressure gradients in the extravascular space on fluid exchange from capillaries. Starling's hypothesis describes fluid transport through the capillary wall, and D'Arcy's law governs flow in the tissue. Using physiologically reasonable values for the wall and tissue hydraulic conductivities and other parameters, it is shown that the tissue hydrostatic pressure is not uniform throughout the tissue space. The greatest deviations from the background pressure occur near the capillary, and the magnitude of deviations increases with increasing ratios of the two conductivities. The model also shows that the fluid exchange behavior is modified by the presence of other capillaries. This capillary-capillary interaction is influenced by the ratio of conductivities, capillary proximity, and the number of existing capillaries.