Development of a perceptual hyperthermia index to evaluate heat strain during treadmill exercise

Abstract

Fire suppression and rescue is a physiologically demanding occupation due to extreme external heat as well as the additional physical and thermal burden of the protective garments. The hot environment challenges body temperature homeostasis inducing heat stress. Accurate field assessment of hyperthermia is complex and unreliable. Purpose: The present investigation developed a perceptually based hyperthermia metric to measure physiologic exertional heat strain during treadmill exercise. Methods:Sixty-five (28.88 ± 6.75 yrs) female (n=11) and male (n=54) firefighters and non-firefighting volunteers participated in four related thermal stress investigations performing treadmill exercise while wearing thermal protective clothing in a heated room. Physiological and perceptual responses (i.e. body core temperature, perceived exertion, and thermal sensation) were assessed at baseline, 20-mins exercise, and at termination. Results: Perceived exertion increased from baseline (0.24 ± 0.42) to termination (7.43 ± 1.86). Thermal sensation increased from baseline (1.78 ± 0.77) to termination (4.50 ± 0.68). Perceived exertion and thermal sensation were measured concurrently with body core temperature to develop a twodimensional graphical representation of three "colored" exertional heat strain zones. Each exertional heat strain zone was representative of a range of mean body core temperature responses such that green incorporated 36.0 to 37.4°C, yellow incorporated 37.5 to 37.9°C, and red incorporated 38.0 to greater than 40.5°C. Conclusions: A perceptual hyperthermia index (PHI) was developed using ratings of iii perceived exertion and thermal sensation. The PHI can provide a quick and easy momentary assessment of the level of risk for exertional heat strain for firefighters engaged in fire suppression and rescue. This metric may be beneficial in high risk environments that threaten the lives of firefighters.

Practical on-site measurement of heat strain with the use of a perceptual strain index

“…On this basis, the exposure limit of the PeSI ranging from 7 and 8 with the corresponding RPE-TS combinations towards the heavy level of physiological strain (3 < PSI HR ≤ 4) was obtained. Using the similar concept proposed by Gallagher et al (2012), RPE on the horizontal axis and TS on the vertical axis replacing the PeSI values were linked to each physiological strain level (Fig. 3).…”

Questionnaire on Firefighters’ Protective Clothing in China

“…When the core body temperature continues to rise, central nervous system dysfunction will appear. This phase is called heat stroke [21,22]. This section of the questionnaire was dedicated to gathering opinions about heat illness experienced during firefighting.…”

Characterizing a Firefighter’s Immediate Thermal Environment in Live-Fire Training Scenarios

“…Some studies have utilized training drills with environmental temperatures less than 100°C in a live-fire burn structure to simulate fire ground activities [18][19][20][21][22]. More commonly, research groups have used a treadmill protocol in a temperature-controlled ( 25°C to 50°C) room [23][24][25][26][27][28]. While Selkirk and McLellan have shown that the physiological responses to activity in fire fighting PPE is affected by the ambient temperature of the testing environment, there are limited data available upon which to base the representative thermal conditions.…”