Evaluation of structural and thermophysical effects on the measurement accuracy of deep body thermometers based on dual-heat-flux method

Skin-Inspired Thermometer Enabling Contact-Independent Temperature Sensation via a Seebeck-Resistive Bimodal System

Tactile sensation is a powerful method for probing the temperature of an arbitrary object due to its intuitive operating mechanism. However, the disruptive interface commonly formed between the thermometer and the object gives rise to thermal contact resistance, which is the primary source of measurement inaccuracy. Here, we develop a bioinspired bimodal temperature sensor exhibiting robust measurement accuracy by precisely decoupling contact resistance from the associated thermal circuit. In our sensors, a micropatterned resistive thermometer is placed underneath a thermoelectric heat fluxmeter, which resembles thermoreceptors located in human biomembranes. The object temperature is probed by modulating the thermometer temperature within the sensor system and precisely extrapolating the zero-heat flux point of the Seebeck voltage developed across the fluxmeter. At this zero-heat flux point, the object and thermometer temperatures coincide with each other regardless of the contact resistance formed at the fluxmeter-object interface. An experimental study shows that our sensors display excellent measurement accuracy within ∼0.5 K over a wide range of contact resistance values. Our work opens up new avenues for highly sensitive tactile thermal sensation in thermal haptics, medical devices, and robotics if combined with flexible devices.

Wearable Personal Core Body Temperature Measurement Considering Individual Differences and Dynamic Tissue Blood Perfusion

Accurate and continuous measurement of the human core body temperature by a wearable device is of great significance for human health care and disease monitoring. The current wearable thermometers ignore the physiological differences between individuals and the role of blood perfusion in thermoregulation, resulting in insufficient accuracy and limitations in terms of the measurement sites. This study proposed a novel personal model for measuring core body temperature by taking dynamic tissue blood perfusion and individual differences into consideration. The technique facilitates possible accurate core body temperature measurements from the skin surface of the wrist and forehead. First, the personal core body temperature model was established based on the thermal equilibrium between the human body and the measurement device, in which the tissue blood perfusion changes dynamically with tissue temperature. Then, the parameters of the personal model that imply individual physiological differences were obtained based on personal data collected daily. The results show that with the developed personal model, the accuracy of the measured body temperature from the wrist is close to that of the forehead model. The wrist model and the forehead model have a mean absolute error of 0.297 (SD=0.078) C and 0.224 (SD=0.071) C, respectively, which meets the accuracy and robustness requirements of practical applications. The personal models significantly improve the accuracy compared with that of the group model, especially for the wrist model.

Non-invasive and wearable thermometer for continuous monitoring of core body temperature under various convective conditions

We describe the design of a thermometer that can be worn during everyday activities for monitoring core body temperature (CBT) at the skin surface. This sensor estimates the CBT by measuring the heat flux from the body core based on a thermal conductive model. The heat flux is usually affected by the ambient convective conditions (e.g. air conditioner or posture), which in turn affects the model's accuracy. Thus, we analytically investigated heat conduction and designed a sensor interface that would be robust to convection changes. We performed an in vitro experiment and a preliminary in vivo experiment. The accuracy of CBT in an in vitro experiments was 0.1°C for convective values ranging from 0 to 1.2 m/s. The wearable thermometer has high potential as non-invasive CBT monitor.

Evaluation of a noninvasive deep body thermometer in measurement of specific positions

This study tried to address the theoretical issue of a noninvasive deep body thermometer based on dual-heat-flux method about what depth does the thermometer measure and to what extent can it reflect the change of the real core body temperature (CBT). Authors built up two elaborate 3D models incorporated with the statistics of clinical studies and minute description of blood perfusion to mimic the situations when the thermometer was applied to forehead and thorax, respectively. The results based on finite element analysis show that the thermometer can approximate to the frontal bone and reach to the sternum. For the range from 34 to 40 °C, the measuring depth was stable and hardly be influenced by central thermoregulatory system. Furthermore, it is also suggested that the forehead may be suited for intensive CBT monitoring and the thorax is feasible for daily healthcare application.

Wearable deep body thermometers and their uses in continuous monitoring for daily healthcare

This paper introduces noninvasive deep body thermometers suitable for continuous deep body temperature (DBT) measurement. On the basis of their features, they were used in DBT monitoring for daily healthcare. A thermometer based on the dual-heat-flux method (T_DHFM), and an aural canal thermistor (ACT), were used in two studies of daily healthcare. The medical device CoreTemp by Terumo, based on the zero-heat-flux method, was also used for a DBT reference. The first study focused on preventing heat stroke in a high-temperature and high-humidity environment, while the other focused on the temperature monitoring of patients with spinal cord injuries. In the first study, CoreTemp and T_DHFM were used, whereas T_DHFM and ACT were used in the second study. Using the results from these two studies, we discuss the availability and performance of each thermometer and indicate the necessity of an appropriate method of measuring DBT.

A Wearable Thermometry for Core Body Temperature Measurement and Its Experimental Verification

A wearable thermometry for core body temperature (CBT) measurement has both healthcare and clinical applications. On the basis of the mechanism of bioheat transfer, we earlier designed and improved a wearable thermometry using the dual-heat-flux method for CBT measurement. In this study, this thermometry is examined experimentally. We studied a fast-changing CBT measurement (FCCM, 55 min, 12 subjects) inside a thermostatic chamber and performed long-term monitoring of CBT (LTM, 24 h, six subjects). When compared with a reference, the CoreTemp CM-210 by Terumo, FCCM shows 0.07 °C average difference and a 95% CI of [-0.27, 0.12] °C. LTM shows no significant difference in parameters for the inference of circadian rhythm. The FCCM and LTM both simulated scenarios in which this thermometry could be used for intensive monitoring and daily healthcare, respectively. The results suggest that because of its convenient design, this thermometry may be an ideal choice for conventional CBT measurements.

Use of finite element analysis to optimize probe design for double sensor method-based thermometer

Body temperature is an essential vital sign for assessing physiological functions. The double sensor method-based thermometer is a promising technology that may be applicable to body temperature monitoring in daily life. It continuously estimates deep tissue temperature from the intact skin surface. Despite its considerable potential for monitoring body temperature, its key design features have not been investigated. In this study, we considered four design factors: the cover material, insulator material, insulator radius, and insulator height. We also evaluated their effects on the performance of the double sensor thermometer in terms of accuracy, initial waiting time, and the ability to track changes in body temperature. The probe material and size influenced the accuracy and initial waiting time. Finite element analysis revealed that four thermometers of different sizes composed of an aluminum cover and foam insulator provided high accuracy (<0.1°C) under various ambient temperatures and blood perfusion rates: R=20mm, H=5mm; R=15mm, H=10mm; R=20mm, H=10mm; and R=15mm, H=15mm. The initial waiting time was approximately 10min with almost the same traceability of temperature change. Our findings may provide thermometer manufacturers with new insights into probe design and help them fabricate thermometers optimized for specific applications.