Worker heat stress prevention and work metabolism estimation: comparing two assessment methods of the heart rate thermal component

Abstract

The heart rate thermal component ($\mathrm{\Delta }\mathrm{H}{\mathrm{R}}_{\mathrm{T}}$) can increase with body heat accumulation and lead to work metabolism (WM) overestimation. We used two methods (VOGT and KAMP) to assess $\mathrm{\Delta }\mathrm{H}{\mathrm{R}}_{\mathrm{T}}$ of 35 forest workers throughout their work shifts, then compared $\mathrm{\Delta }\mathrm{H}{\mathrm{R}}_{\mathrm{T}}$ at work and at rest using limits of agreement (LoA). Next, for a subsample of 20 forest workers, we produced corrected WM estimates from $\mathrm{\Delta }\mathrm{H}{\mathrm{R}}_{\mathrm{T}}$ and compared them to measured WM. Although both methods produced significantly different $\mathrm{\Delta }\mathrm{H}{\mathrm{R}}_{\mathrm{T}}$ time-related profiles, they yielded comparable average thermal cardiac reactivity (VOGT: 24.8 bpm °C⁻¹; KAMP: 24.5 bpm °C⁻¹), average $\mathrm{\Delta }\mathrm{H}{\mathrm{R}}_{\mathrm{T}}$ (LoA: 0.7 ± 11.2 bpm) and average WM estimates (LoA: 0.2 ± 3.4 ml O₂ kg⁻¹min⁻¹ for VOGT, and 0.0 ± 5.4 ml O₂ kg⁻¹min⁻¹ for KAMP). Both methods are suitable to assess heat stress through $\mathrm{\Delta }\mathrm{H}{\mathrm{R}}_{\mathrm{T}}$ and improve WM estimation.

Practitioner summary: We compared two methods for assessing the heart rate thermal component ($\mathrm{\Delta }\mathrm{H}{\mathrm{R}}_{\mathrm{T}}$), which is needed to produce a corrected HR profile for estimating work metabolism (WM). Both methods yielded similar $\mathrm{\Delta }\mathrm{H}{\mathrm{R}}_{\mathrm{T}}$ estimates that allowed accurate estimations of heat stress and WM at the group level, but they were imprecise at the individual level.

Abbreviations: AIC: akaike information criterion; bpm: beats per minute; CI: confidence intervals; CV: coefficient of variation in %; CV drift: cardiovascular drift; ΔHR_T: the heart rate thermal component in bpm; ΔHR_T: the heart rate thermal component in bpm; ΔΔHR_T: variation in the heart rate thermal component in bpm; ΔT_C: variation in core body temperature in °C; HR: heart rate in bpm; HRmax: maximal heart rate in bpm; Icl: cloting insulation in clo; KAMP: Kampmann et al. (2001) method to determe ΔHR_T; LoA: Limits of Agreement; PMV-PPD: the Predicted Mean Vote and Predicted Percentage Dissatisfied; PHS: Predicted Heat Strain model; RCM: random coefficients model; SD: standard deviation; TC: core body temperature in °C; TCR: thermal cardiac reactivity in bpm °C⁻¹; τ_ΔHRT: rate of change in the heart rate thermal component in bpm min⁻¹; τ_TC: rate of change in core body temperature in °C min⁻¹; t_α,n-1: Student’s t statistic with level of confidence alpha and n⁻¹ degrees of freedom; TWL: Thermal Work Limit model; $\dot{\mathrm{V}}{\mathrm{O}}_2$: oxygen consumption in ml O₂ kg⁻¹ min⁻¹; $\dot{\mathrm{V}}{\mathrm{O}}_2$ max: maximal oxygen consumption in ml O₂ kg⁻¹ min⁻¹; VOGT: Vogt et al. (1973) method to determine ΔHR_T; WBGT: Wet-Bulb Globe Temperature in °C; WM: work metabolism

Keywords:

• Heart rate thermal component
• work metabolism estimation
• field methodology
• forest work
• heat stress monitoring

Acknowledgements

The authors are grateful to the anonymous reviewers for their insightful and detailed comments. The authors wish to thank Dr. Luc Lebel for his assistance and technical advice regarding forest work operations and Dr. Mario Leone for his technical advice with oxygen consumption measurement with the K4b². They also thank Denise Tousignant (Direction de la recherche forestière) for English editing.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was funded by the Ministère des Forêts, de la Faune et des Parcs; the Fonds de recherche du Québec — Nature et technologies (FRQNT); and the Natural Science and Engineering Research Council of Canada (NSERC).