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 blood now rate is introduced. The measurements were performed with a transcutaneous (tc) PO2-electrode that is capable of heating and measuring local temperature, and it is constructed with a thermostatically controlled cap. The probe was heated electrically to a selected temperature 2-10 degrees above normal skin temperature. When the temperature was stable, the heating element was turned off, and the temperature was registered every 10 s until a stable baseline temperature, T-b, was obtained. T-b was subtracted from the registered temperatures giving Delta Ts that were plotted in a semi-logarithmic diagram. The heat-washout was monoexponential, and the slope was used for calculating blood flow rate in accordance with the principle of Kety, using a known partition coefficient. The method was applied to the forearm in two subjects, and the results were compared to blood flow rates obtained simultaneously 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 coefficient was 0 . 986 at temperature levels of 37-45 degrees C. In the pulp of the thumb, blood flow rates, in arteriovenous anastomoses, were estimated in two subjects by subtracting the capillary blood flow rate, measured by Xe-133-washout, from the total cutaneous blood flow rate, measured 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.