HEAT-WASHOUT - A NEW METHOD FOR MEASURING CUTANEOUS BLOOD-FLOW RATE IN AREAS WITH AND WITHOUT ARTERIOVENOUS ANASTOMOSES

A new method, the heat-washout method, for measuring total cutaneous b lood now rate is introduced. The measurements were performed with a tr anscutaneous (tc) PO2-electrode that is capable of heating and measuri ng local temperature, and it is constructed with a thermostatically co ntrolled cap. The probe was heated electrically to a selected temperat ure 2-10 degrees above normal skin temperature. When the temperature w as stable, the heating element was turned off, and the temperature was registered every 10 s until a stable baseline temperature, T-b, was o btained. T-b was subtracted from the registered temperatures giving De lta Ts that were plotted in a semi-logarithmic diagram. The heat-washo ut was monoexponential, and the slope was used for calculating blood f low rate in accordance with the principle of Kety, using a known parti tion coefficient. The method was applied to the forearm in two subject s, and the results were compared to blood flow rates obtained simultan eously by the Xe-133-washout method in the same area. The equation of the regression line was y=2 . 5+0 . 968X and the correlation coefficie nt was 0 . 986 at temperature levels of 37-45 degrees C. In the pulp o f the thumb, blood flow rates, in arteriovenous anastomoses, were esti mated in two subjects by subtracting the capillary blood flow rate, me asured by Xe-133-washout, from the total cutaneous blood flow rate, me asured by heat-washout. Due to a relatively low diffusions coefficient for Xe-133 compared to heat, Xe-133 cannot be used for measurement of blood flow rate in arteriovenous anastomoses.