Effect of Increased Venous Pressure on the Hydrostatic and Colloid Osmotic Pressure in Subcutaneous Interstitial Fluid in Rats: Edema-Preventing Mechanisms

Abstract

The purpose of the present experiments was to study the effect of a rise in local venous pressure (P_v) on interstitial fluid hydrostatic (P_i) and colloid osmotic pressure (COP_i) in rats. The P_v of the hind limb was increased by ligating the iliac veins and the inferior caval vein. Interstitial fluid for protein and COP determination was sampled from subcutaneous tissue of the hind limbs by a wick technique, and the P_i was measured by a modified Scholander technique. When the P_v was increased from 3 to 12 mm Hg, the COP_i fell from 9 to 4 mm Hg. The P_i averaged -1 mm Hg under control conditions and was unchanged when the P_v was elevated to 12 mm Hg. No edema was detected. Higher rises in venous pressures resulted in further but less pronounced falls in interstitial fluid COP. Edema developed and the P_i increased to +1 to 2 mm Hg. The results show that the fall in COP_i is an important edema-preventing factor during increased venous pressure, whereas a rise in P_i only seems to oppose further increase of an already existing edema.

Key Words:

• Capillary filtration
• tissue pressure
• transcapillary fluid balance
• wick method