Ability to Discriminate Between Sustainable and Unsustainable Heat Stress Exposures- Part 2: Physiological Indicators

作者：Garzon Villalba Ximena P; Wu Yougui; Ashley Candi D; Bernard Thomas E^*

来源：Annals of Work Exposures and Health, 2017, 61(6): 621-632.

DOI：10.1093/annweh/wxx035

• heat strain
• heat stress
• Physiological responses
• ROC
• sustainable
• unsustainable

Objectives: There are times when it is not practical to assess heat stress using environmental metrics and metabolic rate, and heat strain may provide an alternative approach. Heat strain indicators have been used for decades as tools for monitoring physiological responses to work in hot environments. Common indicators of heat strain are body core temperature (assessed here as rectal temperature T-re), heart rate (HR), and average skin temperature (T-sk). Data collected from progressive heat stress trials were used to (1) demonstrate if physiological heat strain indicators (PHSIs) at the upper limit of Sustainable heat stress were below generally accepted limits; (2) suggest values for PHSIs that demonstrate a Sustainable level of heat stress; (3) suggest alternative PHSIs; and (4) determine if metabolic rate was an effect modifier.
Methods: Two previous progressive heat stress studies included 176 trials with 352 pairs of Sustainable and Unsustainable exposures over a range of relative humidities and metabolic rates using 29 participants. To assess the discrimination ability of PHSIs, conditional logistic regression and stepwise logistic regression were used to find the best combinations of predictors of Unsustainable exposures. The accuracy of the models was assessed using receiver operating characteristic curves.
Results: Current recommendations for physiological heat strain limits were associated with probabilities of Unsustainable greater than 0.5. Screening limits for Sustainable heat stress were T-re of 37.5 degrees C, HR of 105 bpm, and T-sk of 35.8 degrees C. T-sk alone resulted in an area under the curve of 0.85 and the combination of T-sk and HR (area under the curve = 0.88) performed the best. The adjustment for metabolic rate was statistically significant for physiological strain index or Delta Tre-sk as main predictors, but its effect modification was negligible and could be ignored.
Conclusions: Based on the receiver operating characteristic curve, PHSIs (T-re, HR, and T-sk) can accurately predict Unsustainable heat stress exposures. T-sk alone or in combination with HR has a high sensitivity, and makes better discriminations than the other PHSIs under relatively constant exposure (metabolic rate and environment) for an hour or so. Screening limits with high sensitivity, however,have low thresholds that limit utility. To the extent that the observed strain is low, there is good evidence that the exposure is Sustainable.

• 出版日期2017-7