Validity of a noninvasive estimation of deep body temperature when wearing personal protective equipment during exercise and recovery

Abstract

Background: Deep body temperature is a critical indicator of heat strain. However, direct measures are often invasive, costly, and difficult to implement in the field. This study assessed the agreement between deep body temperature estimated from heart rate and that measured directly during repeated work bouts while wearing explosive ordnance disposal (EOD) protective clothing and during recovery.

Methods: Eight males completed three work and recovery periods across two separate days. Work consisted of treadmill walking on a 1% incline at 2.5, 4.0, or 5.5 km/h, in a random order, wearing EOD protective clothing. Ambient temperature and relative humidity were maintained at 24 °C and 50% [Wet bulb globe temperature (WBGT) (20.9 ± 1.2) °C] or 32 °C and 60% [WBGT (29.0 ± 0.2) °C] on the separate days, respectively. Heart rate and gastrointestinal temperature (T_GI) were monitored continuously, and deep body temperature was also estimated from heart rate (ECTemp).

Results: The overall systematic bias between T_GI and ECTemp was 0.01 °C with 95% limits of agreement (LoA) of ±0.64 °C and a root mean square error of 0.32 °C. The average error statistics among participants showed no significant differences in error between the exercise and recovery periods or the environmental conditions. At T_GI levels of (37.0-37.5) °C, (37.5-38.0) °C, (38.0-38.5) °C, and > 38.5 °C, the systematic bias and ± 95% LoA were (0.08 ± 0.58) °C, (- 0.02 ± 0.69) °C, (- 0.07 ± 0.63) °C, and (- 0.32 ± 0.56) °C, respectively.

Conclusions: The findings demonstrate acceptable validity of the ECTemp up to 38.5 °C. Conducting work within an ECTemp limit of 38.4 °C, in conditions similar to the present study, would protect the majority of personnel from an excessive elevation in deep body temperature (> 39.0 °C).

Keywords: Body core temperature; Explosive ordnance disposal; Heat strain; Heat stress; Kalman filter; Protective clothing.

Fig. 1

Individual traces of T_GI (blue line), ECTemp (orange line), and heart rate (green line) in WBGT 21 °C (a) and 29 °C (b) conditions. P1-P8 represent each participant, 1 to 8. RMSE: Root mean squared error; ECTemp: Estimated core temperature; WBGT: Wet bulb globe temperature

Fig. 2

Scatterplot (left), frequency distribution (middle), and Bland-Altman plot (right) of T_GI and ECTemp throughout both exercise and recovery periods in conditions of WBGT 21 °C (Top) and 29 °C (Bottom). The difference was calculated as ECTemp minus T_GI