Noninvasive Measurement of Core Body Temperature from the Human Forearm

The human core body temperature (CBT) is one of the most fundamental indications for determining a subject’s health condition [1]. The traditional invasive method of measuring CBT is inserting a temperature probe into specific sites of the human body (<i>e.g.</i>, esophagus, rectum, axilla, and tympanic membrane). To overcome the downsides of invasive methods like discomfort and poor standards of hygiene, researchers have developed noninvasive CBT sensors including the zero-heat-flux sensor and the double sensor. The major drawback of these noninvasive CBT sensors is that they hinder the subject’s operative capabilities as they must be attached to regions close to the internal organs (<i>e.g.</i>, forehead and thorax). In this study, we present a noninvasive method of determining the subject’s CBT by gathering certain thermophysical data at the forearm (<i>i.e.</i>, the skin temperature, heat flux, and blood perfusion rate). Under a thermoneutral state, experimental data show that the CBT region extends out to the extremities, which includes the large arteries at the forearm. We have measured the surface temperature and heat flux with a resistance temperature detector and a thermopile heat flux sensor, respectively. Also, we have incorporated a way to measure the blood perfusion rate thermally <i>via</i> sinusoidal heating. With the measured data, solving the Pennes’ bioheat equation in a heterogeneous medium to account for variability in tissue layers allows for the estimation of CBT within a few degrees. The study was performed on human subjects for a period of approximately forty minutes. One subject showed promising results with estimated average range of CBT of 0.73°C. For periods where the subject’s actual CBT (axillary temperature) did not fall within the estimated range, the average deviation away from the actual CBT was only 0.24°C. This study leaps towards a more convenient way of gaining the subject’s health condition.<br/><br/>[1] G. Park, J. Kim, S. Woo, J. Yu, S. Khan, S.K. Kim, H. Lee, S. Lee, B. Kwon, W. Kim, <i>Applied Energy</i> <b>323</b>, 119609 (2022)