Transcapillary Exchange Rates of Deuterium Oxide and Thiocyanate in the Forearm of Man

Abstract

A method is described for estimating the exchange rates of labeled filterable substances through capillary walls. The method was applied in studying the transcapillary exchange rates of deuterium oxide and thiocyanate ion, and indicated that approx. 95% of the heavy water and 50% of the thiocyanate ion transferred out of the blood in a single circulation through the forearm. The major portion of the deuterium oxide which passed through the capillary walls of the forearm did not return rapidly to the circulation. The rapidity and magnitude of the water exchange across capillary walls observed in these expts. suggest that simple diffusion rather than hydrostatic and osmotic pressures is the major influence governing such fluid transfer.