Interstitial fluid pressure.

Fluid movement through the capillary membrane has been measured in the lower legs of dogs by using implanted, perforated capsules as internal plethysmographs. Utilizing this procedure it was possible to compare the effects of changes in interstitial fluid pressure with the effects of changes in venous pressure and arterial pressure on movement of fluid through the capillary membrane. A decrease in interstitial fluid pressure of 1 mm Hg increased the filtration of fluid out of the capillaries 1.20 as much as did 1 mm Hg increase in venous pressure. The filtration coefficient for fluid movement through the capillary wall per unit change in interstitial fluid pressure was 0.058 yxliter/min per mm Hg per g of tissue. This value is in the same range as filtration coefficients that others have determined following changes in capillary pressure. ADDITIONAL