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

Abstract

The heart rate thermal component ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>Δ</mml:mi><mml:mi>H</mml:mi><mml:msub><mml:mrow><mml:mi>R</mml:mi></mml:mrow><mml:mrow><mml:mi>T</mml:mi></mml:mrow></mml:msub></mml:math> ) can increase with body heat accumulation and lead to work metabolism (WM) overestimation. We used two methods (VOGT and KAMP) to assess <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>Δ</mml:mi><mml:mi>H</mml:mi><mml:msub><mml:mrow><mml:mi>R</mml:mi></mml:mrow><mml:mrow><mml:mi>T</mml:mi></mml:mrow></mml:msub></mml:math> of 35 forest workers throughout their work shifts, then compared <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>Δ</mml:mi><mml:mi>H</mml:mi><mml:msub><mml:mrow><mml:mi>R</mml:mi></mml:mrow><mml:mrow><mml:mi>T</mml:mi></mml:mrow></mml:msub></mml:math> at work and at rest using limits of agreement (LoA). Next, for a subsample of 20 forest workers, we produced corrected WM estimates from <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>Δ</mml:mi><mml:mi>H</mml:mi><mml:msub><mml:mrow><mml:mi>R</mml:mi></mml:mrow><mml:mrow><mml:mi>T</mml:mi></mml:mrow></mml:msub></mml:math> and compared them to measured WM. Although both methods produced significantly different <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>Δ</mml:mi><mml:mi>H</mml:mi><mml:msub><mml:mrow><mml:mi>R</mml:mi></mml:mrow><mml:mrow><mml:mi>T</mml:mi></mml:mrow></mml:msub></mml:math> time-related profiles, they yielded comparable average thermal cardiac reactivity (VOGT: 24.8 bpm °C^-1; KAMP: 24.5 bpm °C^-1), average <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>Δ</mml:mi><mml:mi>H</mml:mi><mml:msub><mml:mrow><mml:mi>R</mml:mi></mml:mrow><mml:mrow><mml:mi>T</mml:mi></mml:mrow></mml:msub></mml:math> (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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>Δ</mml:mi><mml:mi>H</mml:mi><mml:msub><mml:mrow><mml:mi>R</mml:mi></mml:mrow><mml:mrow><mml:mi>T</mml:mi></mml:mrow></mml:msub></mml:math> and improve WM estimation. <b>Practitioner summary:</b> We compared two methods for assessing the heart rate thermal component ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>Δ</mml:mi><mml:mi>H</mml:mi><mml:msub><mml:mrow><mml:mi>R</mml:mi></mml:mrow><mml:mrow><mml:mi>T</mml:mi></mml:mrow></mml:msub></mml:math> ), which is needed to produce a corrected HR profile for estimating work metabolism (WM). Both methods yielded similar <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>Δ</mml:mi><mml:mi>H</mml:mi><mml:msub><mml:mrow><mml:mi>R</mml:mi></mml:mrow><mml:mrow><mml:mi>T</mml:mi></mml:mrow></mml:msub></mml:math> estimates that allowed accurate estimations of heat stress and WM at the group level, but they were imprecise at the individual level. <b>Abbreviations:</b> 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; <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mover><mml:mrow><mml:mi>V</mml:mi></mml:mrow><mml:mo>̇</mml:mo></mml:mover><mml:msub><mml:mrow><mml:mi>O</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:math> : oxygen consumption in ml O₂ kg^-1 min^-1; <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mover><mml:mrow><mml:mi>V</mml:mi></mml:mrow><mml:mo>̇</mml:mo></mml:mover><mml:msub><mml:mrow><mml:mi>O</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:math> 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.