Validity and reliability of a protocol to establish human critical environmental limits (PSU HEAT Project)

Abstract

The PSU HEAT protocol has been used to determine critical environmental limits, i.e., those combinations of ambient temperature and humidity above which heat stress becomes uncompensable and core temperature rises continuously. However, no studies have rigorously investigated the reliability and validity of this experimental protocol. Here, we assessed the (1) between-visit reliability and (2) validity of the paradigm. 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. After an equilibration period, either dry-bulb temperature (Tdb) was increased every 5 min while ambient water vapor pressure (Pa) was held constant (Tcrit experiments) or Pa was increased every 5 min while Tdb was held constant (Pcrit experiments) until an upward inflection in gastrointestinal temperature (Tgi) was observed. For reliability experiments, 11 subjects repeated the same protocol on a different day. For validity experiments, 10 subjects performed a Tcrit experiment at their previously determined Pcrit or vice versa. The between-visit reliability (intraclass correlation coefficient, ICC) for critical environmental limits was 0.98. Similarly, there was excellent agreement between original and validity trials for Tcrit (ICC = 0.95) and Pcrit (ICC = 0.96). Further, the wet-bulb temperature at the Tgi inflection point was not different during reliability (p = 0.78) or validity (p = 0.32) trials compared to original trials. These findings support the reliability and validity of this experimental paradigm for the determination of critical environmental limits for maintenance of human heat balance.

Utility of the Heat Index in defining the upper limits of thermal balance during light physical activity (PSU HEAT Project)

“…The ambient T db and P a at the time of T c inflection were considered the critical environmental limits for heat stress compensability below, which subjects are in thermally safe conditions and above which their bodies no longer have the ability to physiologically maintain a stable core temperature. We have demonstrated excellent validity and reliability of this experimental protocol (Cottle et al 2021). There was no solar radiation substitute or forced air movement inside the environmental chamber during experimental trials, though both do impact the human heat balance (Foster et al 2022a(Foster et al , 2022b.…”

Do one-hour exposures provide a valid assessment of physiological heat strain?

“…Studies employing short observation periods (1 h) or progressive stress protocols for detecting the ULPZ (Fig. 1) with exercising (Bernard et al 2008) or sedentary participants (Gagnon et al 2016;Ravanelli et al 2015) will have to scrutinize their protocols for validity and reliability (Cottle et al 2022), especially concerning the time course of the physiological response under constant heat stress conditions for ensuring the establishment of a steady-state. Otherwise, these procedures may underestimate the strain level.…”

A Novel Conceptual Model for Human Heat Tolerance

“…An example time course for T c is shown in Figure 2. We previously have reported excellent reliability and validity of this protocol to identify CELs (37).…”