EFFECTS OF COLD ON MICROVASCULAR FLUID MOVEMENT IN THE CAT LIMB

We investigated the effects of low temperatures down to approximately 5-degrees-C on postcapillary resistance (Rv) and isogravimetric capillary pressure (Pci) in the isolated constant-flow-perfused cat hindlimb to see if a low-temperature-induced increase in Rv and decrease in Pci could lead to an increase in filtration pressure and edema formation. A low-viscosity perfusate (20% cat plasma, 80% albumin-electrolyte solution; viscosity approximately 1 cP) was used. Isoproterenol (10(-7) M) was added to vasodilate the limb and achieve normal microvascular permeability. Rv and Pci were estimated from the slope and zero-flow intercept, respectively, of the straight-line fit to the isogravimetric venous pressure vs. flow data. Rv and Pci were determined in each experiment at an initial 37-degrees-C control, at a lowered temperature (30, 23, 15, or 5-10-degrees-C), and then at 37-degrees-C again. The ratio of Rv at the low temperatures relative to the initial 37-degrees-C control increased almost linearly as temperature was reduced. The increase was 3.4 times control at the lowest temperature. Pci decreased significantly from control only in the lowest temperature group where the change was -5.4 mmHg. Analysis of our data with the low-viscosity perfusate shows that the limb can become edematous if temperature is lowered to approximately 5-degrees-C unless venous pressure (PV) is lowered to venous collapse and flow reduced to less than approximately 20 ml.min-1.100 g-1. Extrapolation of our results to a high viscosity perfusate (whole blood; viscosity > 3 cP at 37-degrees-C) at approximately 5-degrees-C shows that Pv must be reduced to venous collapse and flow to less than approximately 6 ml.min-1.100 g-1 to maintain isogravimetric conditions. Hence, a high Rv and reduced Pci due to perfusion with viscous fluids at low temperature can lead to edema under constant-flow conditions.