Effect of Venous Pressure on Mean Capillary Pressure and Vascular Resistance in the Intestine

Abstract

Elevation of venous pressure in the intestine increases capillary pressure by amounts that average 62% of the venous pressure increment. The relation may be expressed as P_c = 9.7 + 0.62 P_v, where P_c represents the mean capillary pressure and P_v represents venous pressure (both expressed in mm Hg). The increase of capillary pressure is less than expected for a rigid system and less than reported for skeletal muscle. This attenuation of the effect of increments of venous pressure on capillary blood pressure is due to precapillary constriction and postcapillary dilation, with the latter playing the dominant role. Measurement of resistance in a segment of the venous vasculature confirmed this and also demonstrated that most of the reduction of resistance occurs in venous vessels with diameters greater than 0.5 mm.