Real-time core body temperature estimation from heart rate for first responders wearing different levels of personal protective equipment

First responders often wear personal protective equipment (PPE) for protection from on-the-job hazards. While PPE ensembles offer individuals protection, they limit one's ability to thermoregulate, and can place the wearer in danger of heat exhaustion and higher cardiac stress. Automatically monitoring thermal–work strain is one means to manage these risks, but measuring core body temperature (T_c) has proved problematic. An algorithm that estimates T_c from sequential measures of heart rate (HR) was compared to the observed T_c from 27 US soldiers participating in three different chemical/biological training events (45–90 min duration) while wearing PPE. Hotter participants (higher T_c) averaged (HRs) of 140 bpm and reached T_c around 39°C. Overall the algorithm had a small bias (0.02°C) and root mean square error (0.21°C). Limits of agreement (LoA ± 0.48°C) were similar to comparisons of T_c measured by oesophageal and rectal probes. The algorithm shows promise for use in real-time monitoring of encapsulated first responders.