STUDIES ON CAPILLARY PERMEABILITY WITH TRACER SUBSTANCES

Abstract

The unique advantages of the tracer technique for measuring capillary permeability have been clearly stated by Hahn and Hevesy (1941). Let us suppose that we wish to measure the rate of escape of the sodium ion from the blood plasma across the capillary wall into the extravascular fluid. We might propose to do this by injecting sodium chloride intravenously and by measuring the subsequent decline in concentration of sodium in the plasma. This approach would carry with it, however, two uncertainties. Unless the normal level of sodium in the plasma were considerably exceeded, quantitative analysis for excess sodium would present difficulties and excess sodium chloride in the plasma would likely be followed by a shift of water from the extravascular fluid into the plasma. Decrease in sodium concentration in the plasma would consequently be due to the additive effect of two rates, the rate of movement of water into the...