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Critical Environmental Limit Protocol: Validity and Reliability (PSU HEAT)
Author(s) -
Cottle Rachel M.,
Wolf S. T.,
Lichter Zachary S.,
Kenney W. L.
Publication year - 2022
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.2022.36.s1.r2411
Subject(s) - repeatability , heat stress , inflection point , reliability (semiconductor) , environmental stress , constant (computer programming) , chemistry , thermodynamics , environmental science , statistics , mathematics , atmospheric sciences , physics , computer science , power (physics) , geometry , environmental protection , programming language
With increasing average global temperatures and greater frequency, duration, and severity of heat waves, there is an urgent need to better understand the specific environmental temperatures that place humans at greater risk of heat‐related morbidity and mortality. An incremental heat stress protocol can be used to establish critical environmental limits for human heat exchange, i.e., those combinations of ambient temperature and humidity above which heat stress becomes uncompensable and, therefore, unsafe. However, no studies have rigorously investigated the reliability and validity of this experimental paradigm. PURPOSE Here, we assessed the (1) between‐visit repeatability and (2) validity of an experimental paradigm that either holds ambient vapor pressure (P a ) constant and incrementally increases dry‐bulb temperature (T db ) or vice versa. METHODS Twelve subjects (5M/7W; 25±4 yr) completed a progressive heat stress protocol during which they walked on a treadmill (2.2 mph, 3% gradient) in a controllable environmental chamber while gastrointestinal temperature (T gi ) was continuously monitored. After an equilibration period, the progressive heat stress protocol involved increasing T db every 5 min while P a was held constant (T crit experiments), or increasing P a every 5 min while T db was held constant (P crit experiments), until an upward inflection and continuous rise in T gi was observed. The T crit or P crit was identified as the average T db or P a , respectively, across the 2 min preceding the T gi inflection point. For repeatability experiments, 11 subjects returned to the lab to repeat the same protocol as their first visit. For validity experiments, 10 subjects returned to the lab for a progressive heat stress trial in which T db or P a was held constant at the T crit or P crit value from their first visit. RESULTS The between‐visit repeatability for critical environmental limits was excellent (ICC = 0.98). Similarly, there was excellent agreement between original and validity trials for T db (ICC = 0.95) and P a (ICC = 0.96) at the T gi inflection point. Furthermore, the wet‐bulb temperature at the T gi inflection point was not different during reliability (p = 0.78) or validity (p = 0.32) trials compared to original trials. CONCLUSION Together, these data provide strong evidence that this experimental paradigm is rigorous, reliable, and valid, supporting its use to investigate critical environmental limits to the maintenance of heat balance.