Wearable Multimodal Sensor Probe for Monitoring Core Body Temperature, Electrocardiogram, Heart Rate, and Sweat Rate

Global warming and the associated increase in heatwaves have made the prevention of heat-related illnesses such as heatstroke a critical global challenge. Monitoring physiological indicators such as core body temperature, heart rate, and sweat rate is beneficial for preventing excessive accumulation of heat stress and ensuring safe activities in hot environments. However, existing methods typically require multiple separate sensors, limiting their practicality for real-world applications. In this study, we describe the development of a compact and easy-to-use wearable multimodal sensor probe capable of simultaneously measuring the core body temperature, electrocardiogram, heart rate, and sweat rate. The prototype features an innovative design that integrates a heat flux probe for simultaneous measurement of the core body temperature and cardiac potentials with a computational model for estimating the sweat rate. Validation experiments were conducted with ten healthy adult men performing cycling exercises under controlled environmental conditions, with the accuracy of each measurement obtained from the prototype evaluated by comparison with reference values. The results showed root mean squared errors of 0.087°C for core body temperature and 131 g for total water loss, both surpassing the accuracy of previous studies. However, the prototype exhibited a tendency to overestimate the core body temperature and sweat rate during the exercise and post-exercise recovery phases compared to the resting condition before exercise. This was attributed to thermoregulatory responses, such as evaporative heat loss from sweating and increased skin blood flow, during exercise and recovery. Despite some remaining challenges in validation, this study represents a significant advancement in wearable sensor technology by offering a practical and comprehensive solution for real-time monitoring in hot environments. The proposed system has the potential to contribute to heat stress prevention in occupational, sports, and everyday settings.