A new noninvasive technique for heat-flux-based deep body thermometry together with possible estimation of thermal resistance of the skin tissue

A new noninvasive core-thermometry technique, based on the use of two heat flux sensors with different very low thermal resistances, is proposed. Thermodynamically derived equations, using a pair of skin temperatures and heat fluxes detected from the sensors, can give the estimated deep body temperature (DBT) together with thermal resistance of the skin tissue itself. The validity and accuracy of this method are firstly investigated through in vitro experiments using a tissue phantom model and, secondly, as in vivo comparisons with sublingual ( T sub ) or rectal temperature ( T rec ) measurements in 9 volunteers, attaching the sensors around the upper sternum or the nape. Model experiments showed a good agreement between the measured and estimated temperatures, ranging from approximately 36 to 42 ℃. In vivo experiments demonstrated linear correlations between the estimated DBT and both T sub and T r ec values, though the estimated DBT was 0.13 ℃ higher than T sub and 0.42 ℃ lower than T rec on average. The results also strongly suggested the possibility to estimate the tissue thermal resistance; this is discussed herein. Although further in vivo experiments under various environmental conditions are necessary, this method appears highly promising as an accurate, useful and convenient core-thermometry system for medical and healthcare settings. Graphical Abstract Overview drawing of a new deep body thermometry technique from the skin surface using two heat flux sensors with different very low thermal resistances shown in the upper left part. In vivo experiments demonstrated a good agreement between the measured (sublingual and rectal) and estimated temperatures shown in right upper part. The results also strongly suggested the possibility to estimate the skin tissue thermal resistance and this is described in detail in this paper. The present method is highly promising as an accurate, useful and convenient core-thermometry system for medical and healthcare settings and could be used in daily life through further development as shown in the lower right part.