Validity of a wearable core temperature estimation system in heat using patch-type sensors on the chest

This study aimed to evaluate the reliability of a patch-type sensor on the upper chest region that uses a dual-heat-flux method to estimate core temperature under various heat conditions. The participants' esophageal and rectal temperatures (T_eso and T_rec) were measured with real-time monitoring of predicted core temperature (T_pre) using the patch. Twenty-one volunteers wearing work clothes and nine volunteers wearing protective clothing walked (5.0 km/h) for an hour at 35 °C. During exercise, T_eso increased to 37.9 ± 0.3 °C and 38.2 ± 0.2 °C for each group, respectively. The root mean squared errors (RMSEs) were 0.18 ± 0.05 °C and 0.25 ± 0.08 °C between T_eso and T_pre and were 0.31 ± 0.10 °C and 0.34 ± 0.11 °C between T_rec and T_pre in each clothing condition, respectively. In addition, 11 volunteers walked for an hour at 30 °C or 40 °C. The T_eso during exercise increased to 37.7 ± 0.3 °C and 38.2 ± 0.3 °C, respectively. The RMSEs were 0.23 ± 0.10 °C and 0.18 ± 0.05 °C between T_eso and T_pre in each ambient temperature condition, respectively. Furthermore, eight volunteers performed an arm-cranking exercise (60 W) for 30 min at 35 °C. The T_eso increased to 37.9 ± 0.2 °C during exercise. The RMSEs were 0.22 ± 0.07 °C between T_eso and T_pre. The proportions of all paired measurements differing by less than the predefined threshold for validity of ≤ 0.3 °C were 85 ± 18% between T_eso and T_pre. These data indicate that the patch is capable of providing a moderate estimate of core temperature during low-intensity and acute exercise under heat conditions.