Transcapillary protein leakage and fluid movement: Effect of venous pressure

The effect of elevating venous pressure (ΔP_v) on the transcapillary escape of albumin (Q_T) in control and papverinized gracilis muscles perfused at constant flow was determined by means of direct monitoring of the rate of accumulation of tissue ¹²⁵I-labeled albumin radioactivity. Simultaneously, transcapillary fluid movement (FM) was assessed volumetrically. Under control isovolumetric conditions, Q_T = 2.25 mg/min · 100 g. In addition to causing an FM of 0.03 ml/min · 100 g · mm Hg, increasing P_v enhanced Q_T by 0.06 mg/min · 100 g · mm Hg. Papverinization itself decreased Q_T to 2.0 mg/min · 100 g and affected FM only slightly. However, the superposition of P_v elevation caused a FM of 0.008 ml/min · 100 g · mm Hg and resulted in Q_T increasing by 0.29 mg/min · 100 g · mm Hg. The results of this study indicate that Q_T is sensitive to changes in microvascular hemodynamics, and thus changes in microvascular pressure may affect FM in two ways, first by increasing the transcapillary pressure gradient and second by augmenting Q_T which may superimpose an oncotic adjunct to FM.