Peripheral circulatory effects of pump perfusion on cat skeletal muscle with and without prostacyclin

Reflection coefficient for albumin and capillary fluid permeability in cat calf muscle after traumatic injury

Surgery and traumatic injury are often followed by tissue oedema and a low plasma albumin concentration, indicating leakage of fluid and proteins from the intravascular to the interstitial space. Transcapillary leakage can be referred to as an increase in capillary hydraulic conductance and/or a decrease in the reflection coefficient for plasma macromolecules. This study evaluates if time-dependent variations in the reflection coefficient for albumin and capillary hydraulic conductance can be confirmed experimentally following a surgical trauma using a blood perfused cat skeletal muscle in vivo preparation. The hydraulic conductance was estimated by the capillary filtration coefficient, and was used to evaluate variation in capillary fluid permeability. According to the Starling fluid equilibrium, the ratio between the reflection coefficients for albumin on two occasions can be calculated from the maximum osmotic absorption rates induced by a fixed intravenous bolus infusion of albumin (0.5 g kg(-1)) and from the capillary filtration coefficients. We found a decrease in the reflection coefficient of about 30% up to 10 h after the preparation. The capillary filtration coefficient showed no significant change over time, but decreased by 5-10% following the albumin infusion. We conclude that: (1) the reflection coefficient for albumin is reduced after a trauma, whereas the effects on the capillary fluid permeability are small, (2) albumin in plasma contributes to preserve normal capillary fluid permeability and, (3) the model seems to be useful for evaluation of relative variations in the reflection coefficient for albumin.

The capillary filtration coefficient for evaluation of capillary fluid permeability in cat calf muscles

Measuring the capillary filtration coefficient (CFC) from the transvascular fluid filtration following a fixed increase in transcapillary hydrostatic pressure is a common method to estimate capillary hydraulic permeability (conductivity) in an organ. Constant flow pump perfusion with an artificial perfusate and a maximally dilated vascular bed are often used in CFC studies to avoid influence on CFC of variations in vascular tone, blood flow and perfusion pressure. The present study evaluates if capillary hydraulic conductivity can be estimated by the CFC method, when analyzed on a denervated cat skeletal muscle with quite well-preserved local vascular control and perfused with autologous blood. CFC was estimated by increasing venous pressure and by decreasing tissue pressure, and both during autoperfusion and pressure controlled pump perfusion. A constant filtration rate was achieved 3-4 min after the transcapillary pressure elevation, giving a CFC around 0.0090 mL min-1 mmHg-1 100 g. The CFC did not change with arterial pressure or with reduced vascular tone using the tissue pressure method, but decreased slightly with increased arterial pressure and reduced vascular tone using the venous pressure method. CFC variations with arterial pressure were larger during pump perfusion in which myogenic reactivity is depressed, indicating that influence of myogenic tone on CFC is small. We conclude that CFC can be used to evaluate capillary hydraulic conductivity, and also when arterial pressure, vascular tone and blood flow are altered within reasonable physiological limits during the experiment, and the tissue pressure method and autoperfusion is to be preferred.