Thermal fields and heat generation effects in tissue, awake and under halothane anesthesia

In order to further document the heat generation terms used in models predicting heat transmission in tissue, a series of temperature fields were generated and measured in cat brain with an implantable cylindrical source and thermocouple apparatus. The experimental technique allowed measurements to be made under fully awake in vivo conditions as well as for 3 to 45% levels of halothane anesthesia. Fields resulting from probe forcing function temperatures of 4 degrees C, 18 degrees C, and 28 degrees C were warmer in the anesthetized tissue indicating an increase in heat generation resulting from blood flow and metabolic heat. Values of the heat generation were obtained by applying the Bio-Heat Equation directly to the experimental data. A simple blood flow heat generation model gave a reasonable prediction of the heat generation in a temperature range lower than 3 to 4 degrees C below the inlet blood temperature, and with a Q10 equals 3 variation of blood flow rate with temperature. Results also indicate that the heat generation effect under halothane anesthesia conditions are such that the use of the apparent property concept in thermal modeling may not be valid.