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 pressure (Pv) on interstitial fluid hydrostatic (Pi) and colloid osmotic pressure (COPi) in rats. The Pv 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 Pi was measured by a modified Scholander technique. When the Pv was increased from 3 to 12 mm Hg, the COPi fell from 9 to 4 mm Hg. The Pi averaged -1 mm Hg under control conditions and was unchanged when the Pv 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 Pi increased to +1 to 2mm Hg. The results show that the fall in COPi is an important edema-preventing factor during increased venous pressure, whereas a rise in Pi only seems to oppose further increase of an already existing edema.

Transcapillary fluid flux and inflammatory response during neonatal therapeutic hypothermia: an open, longitudinal, observational study

“…A small, but detectable, fall in COP i compared with COP p is maintained by removal of albumin or other proteins comparable in size from the interstitium. The reduced COP i and COP p during TH in asphyxiated neonates and the ability of TH to oppose changes in capillary filtration by COP in IF is an edema preventive mechanism demonstrated in animal [ 33 ] and human [ 34 ] studies.…”

Isolation of interstitial fluid from skeletal muscle and subcutis in mice using a wick method

“…Although the importance of the absolute value for COP i is debated in relation to filtration across single capillaries, there is no doubt that this parameter is one of the predictors for the edema-preventive capacity of a tissue (3,6). In rat skin and muscle, edema does not develop until the COP i is reduced from normal values of ϳ10 to ϳ2 mmHg (4,19), which suggests that a decrease in COP i could counteract an increase in capillary pressure or a reduction in COP p of 8 -10 mmHg. An important implication of the present study is that the interstitium in skeletal muscle is able to compensate for a significantly higher increase in net filtration pressure than in skin or subcutis.…”

“…Their absolute mean value for COP i in subcutis was slightly but not significantly lower than our value of 9.1 mmHg for the same tissue. Because COP i varies as a function of COP p (4,11,17), a comparison of the COP i /COP p ratio is more relevant. If related to COP p , their COP i /COP p ratio of 0.42 is significantly lower than our corresponding ratio of 0.49.…”