Mechanics of fluid movement across single capillaries in the rabbit

Abstract

An analysis was made of the factors involved in the net movement of fluid through the walls of single capillaries. The method, as originally developed by Landis, utilized the movement of red blood cells in capillaries immediately after temporary occlusion with a glass microneedle as an indication of the relative predominance of either hydrostatic or colloid osmotic pressures. Comparison of transcapillary fluid movement before and after known osmotic transients with intravenous albumin made it possible to calculate the filtration constant and the net or effective driving pressure in selected capillaries. The filtration constant in the omental capillaries was lowest on the arterial side (2 to 8 × 10 −3 μ/sec) and highest on the venous side (16 to 25 × 10 −3 μ/sec). The effective hydrostatic pressure in the capillaries varied between 28−22 cm H 2O, well above the colloid osmotic pressure of the plasma proteins. The findings reaffirm the need to reconsider the precise application of the linear, constitutive relationship governing transcapillary fluid movement as postulated by Starling.