Importance of Tissue Pressure for the Fluid Equilibrium between the Vascular and Interstitial Compartments in the Small Intestine

Abstract

AbstractThe effect of prolonged elevation of venous outflow pressure on the intestinal filtration capacity was studied on cats. Increases of venous outflow pressure produced a filtration of fluid from the capillaries, but the filtration rate decreased gradually with time and often a new isovolumetric state was reached. In order to study the factors causing this decrease of filtration capacity, pointing to a shift of the Starling equilibrium, an indirect method was used, consisting of stepwise raising and lowering the venous pressure. During this procedure the rate of net fluid transfer upon a given venous pressure level could differ very much, depending on whether this pressure level was reached from a lower or from a higher venous outflow pressure. The transcapillary forces, responsible for these differences of net fluid transfer, amounted to often more than 10mm Hg. This means that some factor, or factors, involved in the Starling equilibrium, must have changed by this amount. It is suggested that increasing tissue pressure is the most important counterforce during outward filtration, caused by a sudden rise of the venous outflow pressure. Evidently, the small intestine is quite well protected against edema, in spite of a very big transcapillary filtration capacity.