Fluid exchange in skeletal muscle with viscoelastic blood vessels.

A mathematical model of capillary-tissue fluid exchange in a viscoelastic blood vessel is presented, and the Landis occlusion experiment is simulated. The model assumes that the fluid exchange is governed by Starling's law and that the protein and red blood cells are conserved in the capillary. Before occlusion, in the steady flow state, the pressure in the capillary decreases from the arterial to venous end due to viscous dissipation. After occlusion a constant pressure is established along the capillary. We assume the capillary to be distensible with viscoelastic wall properties. Immediately following occlusion an instantaneous distension of the capillary occurs. The vessel continues to expand viscoelastically while fluid is filtered for a period of several minutes, until it reaches an equilibrium state. A full numerical solution of the governing equations has been obtained. We use this model to compute the distance variation between two labeled erythrocytes as obtained in the Landis occlusion experiment and compare the results with experimental data obtained recently for the spinotrapezius muscle in our laboratory. The new model can fit the experimental data better than previous models that neglect the distensibility of the capillaries.