scholarly journals The Colloid Osmotic Pressure Across the Glycocalyx: Role of Interstitial Fluid Sub-Compartments in Trans-Vascular Fluid Exchange in Skeletal Muscle

Author(s):  
Fitzroy E. Curry ◽  
C. Charles Michel

The primary purpose of these investigations is to integrate our growing knowledge about the endothelial glycocalyx as a permeability and osmotic barrier into models of trans-vascular fluid exchange in whole organs. We describe changes in the colloid osmotic pressure (COP) difference for plasma proteins across the glycocalyx after an increase or decrease in capillary pressure. The composition of the fluid under the glycocalyx changes in step with capillary pressure whereas the composition of the interstitial fluid takes many hours to adjust to a change in vascular pressure. We use models where the fluid under the glycocalyx mixes with sub-compartments of the interstitial fluid (ISF) whose volumes are defined from the ultrastructure of the inter-endothelial cleft and the histology of the tissue surrounding the capillaries. The initial protein composition in the sub-compartments is that during steady state filtration in the presence of a large pore pathway in parallel with the “small pore” glycocalyx pathway. Changes in the composition depend on the volume of the sub-compartment and the balance of convective and diffusive transport into and out of each sub-compartment. In skeletal muscle the simplest model assumes that the fluid under the glycocalyx mixes directly with a tissue sub-compartment with a volume less than 20% of the total skeletal muscle interstitial fluid volume. The model places limits on trans-vascular flows during transient filtration and reabsorption over periods of 30–60 min. The key assumption in this model is compromised when the resistance to diffusion between the base of the glycocalyx and the tissue sub-compartment accounts for more than 1% of the total resistance to diffusion across the endothelial barrier. It is well established that, in the steady state, there can be no reabsorption in tissue such as skeletal muscle. Our approach extends this idea to demonstrate that transient changes in vascular pressure favoring initial reabsorption from the interstitial fluid of skeletal muscle result in much less fluid exchange than is commonly assumed. Our approach should enable critical evaluations of the empirical models of trans-vascular fluid exchange being used in the clinic that do not account for the hydrostatic and COPs across the glycocalyx.

1980 ◽  
Vol 238 (6) ◽  
pp. H886-H888
Author(s):  
J. L. Christian ◽  
R. A. Brace

Membrane osmometry was used to estimate the four transcapillary Starling pressures in subcutaneous tissue of rats, guinea pigs, and dogs. Isolated subcutaneous tissue samples were either placed on a large-pore or small-pore osmometer that measured the interstitial fluid pressure (Pif) and the difference between the interstitial fluid pressure and the interstitial protein osmotic pressure (Pif-pi if), respectively. The colloid osmotic pressure of the interstitial fluid (pi if) was obtained from the difference in these two pressures. A plasma sample placed on the small-pore osmometer yielded the colloid osmotic pressure of the plasma proteins (pi c). Finally the capillary pressure (Pc) was calculated from the three other Starling forces. In the rat, guinea pig, and dog, respectively, the estimated Starling forces were as follows: Pif -2.2, -2.1, and -4.8 mmHg; pi if, 7.3, 4.8, and 4.4 mmHg; pi c, 21.3, 19.5, and 19.2 mmHg; and Pc, 11.8, 12.6, and 10.0 mmHg. A comparison with data obtained in other studies using different methods shows good agreement and strongly supports membrane osmometry as a method for measuring the Starling pressures in subcutaneous tissue.


1993 ◽  
Vol 265 (6) ◽  
pp. R1318-R1323 ◽  
Author(s):  
M. T. Hamilton ◽  
D. S. Ward ◽  
P. D. Watson

Fluid redistribution in isolated perfused cat calf muscle caused by rapid increases in plasma osmolality was studied using NaCl or sucrose. Extracellular tracers (51Cr-labeled EDTA or [3H]mannitol) were added to the perfusate 90 min before solutes were added, and samples were taken from plasma immediately before osmolality was increased and 17, 40, and 65 min later. Interstitial fluid volume (IFV) was calculated as extracellular volume (ECV) minus plasma volume (Evans blue dye). Total tissue water changes (delta TTW) were measured by continuous recording of tissue weight. Change in intracellular volume (delta ICV) was obtained from delta TTW--delta IFV. TTW, IFV, ICV, and plasma osmolality were in steady state after 17 min. Changes in hydrostatic and colloid osmotic pressure were insignificant in comparison with small-molecule osmotic pressure changes. The apparent volume of TTW participating in the fluid shift averaged 65 +/- 1 ml/100 g (SE) over a wide range of osmolality increases. In contrast to the large changes in TTW, IFV was not altered by osmolality. Thus decreases in TTW were similar to cell dehydration. Hence, increases in plasma volume induced by hypertonic fluids may come entirely at the expense of cell volume, not interstitial volume.


Sign in / Sign up

Export Citation Format

Share Document