Methodology for Calibration and Use of Heat Flux Transducers

摘要

The direct assessment of heat flux from the body is a basic measurement inthermal physiology. Heat flux transducers (HFTs) are being used increasingly for that purpose under different environmental conditions. However, questions have been raised regarding the accuracy of the manufacturer's constant of calibration, and also about the effect of the thermal resistance of the device on the true thermal flux from the skin. Two different types of waterproofed HFTs were checked for their calibration using the Rapid-k thermal conductivity instrument. A detailed description of the methodology used during the calibration is given. A model capable of simulating a large range of tissue insulation was used to study the effect of the underlying tissue insulation on the relative error in thermal flux due to the thermal resistance of the HFTs. The data show that the deviation from the true value of thermal flux increases with the reciprocal of the underlying tissue insulation (r = 0.99, p < 0.001). The underestimation of the heat flux through the skin measured by an HFT is minimal when the device is used on vasoconstricted skin in cool subjects (3 to 13% error), but becomes important when used on warm vasodilated subjects (29 to 35% error), and even more important on metallic skin mannequins (> 60% error). In order to optimize the accuracy of the heat flux measurements by HFTs, it is important to recalibrate the HFTs and to correct the heat flux values for the thermal resistance of the HFT when used on vasodilated tissues.