THE INFLUENCE OF ELEVATED VENOUS PRESSURE ON BLOOD-TISSUE EXCHANGE OF ^<22>Na IN PERFUSED HINDLIMBS OF DOGS
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概要
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In order to study the effect of the increase in venous pressure on the exchange of Na ion between the blood and tissue, the hindlimb of dog was perfused under the condition of constant venous outflow to measure the diffusion capacity (PS, the permeability-surface product) for ^22Na, using 'indicator diffusion' method (with RISA or Evans blue as indicators and ^22NaCl as test substance). As the results, the following findings were obtained; 1) The values of PS, resistance to blood flow, the recovery of indicator sub-stance and outflow-inflow ratio were found reproducible, with coefficient of variation of ±13%, ±16%, ±10%, and ±5%, respectively, in 3 determinations repeated in one and the same dog with normal venous pressure. 2) PS was reduced when the venous pressure was elevated to 200mmH_2O. PS was decreased by about 40% in those hindlimbs where venous congestion was produced with relatively fixed outflow-inflow ratio and indicator recovery fixed at normal levels, namely, a circumstance where the same capillary bed is thought to be subjected to isotope studies in the control state as well as during venous congestion. A comparable decrease in PS occurred even in case of venous congestion associated with a decrease in indicator recovery. 3) Resistance to blood flow was not influenced by venous congestion. 4) In view of these results, it is nearly certain that PS is reduced during venous congestion. It is suggested that the venous congestion leads to a closure of precapillary sphincters, with associated re-distribution of blood flow, in the areas of circulation subjected to a high venous pressure. It is probable that, while the blood flows mainly through nutrient capillaries with higher PS in the control state, the blood flow is re-distributed in favor of vessels with lower PS, such as throughfare channels, during venous congestion.
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