Abstract
Phase change material (PCM) cooling garments’ efficacy is limited by the duration of cooling provided. The purpose of this study was to evaluate the effect of replacing a PCM vest during a rest period on physiological and perceptual responses during explosive ordnance disposal (EOD) related activity. Six non-heat acclimated males undertook three trials (consisting of 2 × 3 × 16.5 min activity cycles interspersed with one 10 min rest period) in 40°C, 12% relative humidity whilst wearing a ≈38 kg EOD suit. Participants did not wear a PCM cooling vest (NoPCM); wore one PCM vest throughout (PCM1) or changed the PCM vest in the 10 min rest period (PCM2). Rectal temperature (Tre), mean skin temperature (Tskin), heart rate (HR), Physiological Strain Index (PSI), ratings of perceived exertion, temperature sensation and thermal comfort were compared at the end of each activity cycle and at the end of the trial. Data displayed as mean [95% CI]. After the rest period, a rise in Tre was attenuated in PCM2 compared to NoPCM and PCM1 (−0.57 [−0.95, −0.20]°C and −0.46 [−0.81, −0.11]°C, respectively). A rise in HR and Tskin was also attenuated in PCM2 compared to NoPCM and PCM1 (−23 [−29, −16] beats⋅min–1 and −17 [−28, −6.0] beats⋅min–1; −0.61 [−1.21, −0.10]°C and −0.89 [−1.37, −0.42]°C, respectively). Resulting in PSI being lower in PCM2 compared to NoPCM and PCM1 (−2.2 [−3.1, −1.4] and –0.8 [−1.3,−0.4], respectively). More favorable perceptions were also observed in PCM2 vs. both NoPCM and PCM1 (p < 0.01). Thermal perceptual measures were similar between NoPCM and PCM1 and the rise in Tre after the rest period tended to be greater in PCM1 than NoPCM. These findings suggest that replacing a PCM vest better attenuates rises in both physiological and perceptual strain compared to when a PCM vest is not replaced. Furthermore, not replacing a PCM vest that has exhausted its cooling capacity, can increase the level of heat strain experienced by the wearer.
Highlights
Wearing personal protective equipment (PPE) in hot environments and/or during high intensity activity can result in the body being unable to maintain thermal balance, which is termed as uncompensable heat strain (UHS; see Cheung et al, 2000 for a review)
Due to technical error and excessive measurement artifacts, one of the subjects heart rate (HR) recordings has been removed from the analysis, reducing the HR and physiological strain index (PSI)
Post hoc pairwise comparisons identified that Tre in PCM2 was lower than not wear a PCM cooling vest (NoPCM) and PCM1 at the end of the trial
Summary
Wearing personal protective equipment (PPE) in hot environments and/or during high intensity activity can result in the body being unable to maintain thermal balance, which is termed as uncompensable heat strain (UHS; see Cheung et al, 2000 for a review). Several cooling strategies have been developed and demonstrated to reduce or attenuate the level of heat strain experienced whilst wearing encapsulating protective clothing resulting in extended tolerance times and/or favorable thermal perceptions (McLellan et al, 1999; Cadarette et al, 2003; Kenny et al, 2011; Watkins et al, 2018; Bach et al, 2019; Maley et al, 2020) One such cooling strategy is personal microclimate cooling garments. When body surface area (BSA) coverage is similar, liquid and air-cooled garments generally provide superior cooling capacity and more favorable physiological responses to that of PCM garments when wearing PPE in hot environments or during high metabolic activities (Chan et al, 2015) Due to their complexity, heavy mass, restriction in mobility, and the cost to procure and maintain liquid and air-cooled garments, PCM garments are generally utilized in the field (Chan et al, 2015)
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