2007, Piran, Slovenia

Environmental Ergonomics XII
Igor B. Mekjavic, Stelios N. Kounalakis & Nigel A.S. Taylor (Eds.), © BIOMED, Ljubljana 2007
rest + 50min harvest work + 10min res; mean work rate 270 W). The subjects hydrated
enough before starting every experiment, and water intake was prohibited during
experimentation.
Rectal temperature (Tre) was measured using a portable thermometer (LT 8A, Gram Corp.,
Japan) at the depth of about 13 cm in the rectum. Skin temperatures (Tsk) were measured for
seven body parts using portable thermometers (LT 8A, Gram Corp., Japan): forehead,
abdomen, forearm, hand, thigh, calf, and foot. Mean skin temperature was calculated
according the Hardy and DuBois’ seven point equation. Heart rate (HR) was measured using
a portable HR monitor (Polar, Polar Electro 3000 INC., USA). The measurements above were
taken every minute. The change of total body mass (∆Wt) was calculated through the
difference between before and after semi-nude body weight using a weighing scale (Sartorius,
F150S, Germany; sensitivity 1g). Subjects recorded their own thermal sensations every ten
minutes using the ISO 9-point scale. The experiment stopped when Tre increased over 39 , Tre
increased more than 2 compared to Tre at the starting point, HR increased over 185 bpm, or
subjects wanted to stop. Body heat storage was derived using the Hardy and DuBois method
(Minard, 1970), and the physiological strain index (PSI: Moran et al., 1998) and modified
Craig index (Hall and Polte, 1960) were calculated:
Heat storage (HS, kcal/m 2 ) = 0.83×(0.8∆Tre+0.2∆mean Tsk) × Weight(kg)/BSA(m 2 )
PSI = 5(Tret Tre0) / (39.5 Tre0) + 5(HRt HR0) / (180 HR0)
Craig index (CI) = HRterminal/100 + ∆Tre + ∆Wt
RESULTS
Table 2 demonstrates the summary of thermal responses in the eight conditions. Rectal
temperature (Tre) was effectively maintained under 38 by wearing PCE. Mean skin
temperature ( _ ,Tsk) and heart rate (HR) also became more stable by wearing PCE. In
particular, when wearing the ‘Hat+ScarfB+Vest’, mean Tsk and HR quickly decreased to the
stable level during mid-rest time. The abdomen and thigh temperatures were significantly
lower in ‘Hat+ScarfB+Vest’, even though PCE were not in direct contact with the abdomen
or thigh. Total body mass loss (∆Wt) was divided into two groups (no cooling and 7 cooling
conditions) by Duncan’s post hoc test.
Also, we compared the efficacy of the different kinds of PCE with HS, PSI and CI (Figure 1).
As results shown in Table 2, there were significant differences between no cooling and the 7
cooling conditions. The heat strain order of the eight conditions were somewhat correlated to
the order of SAcooled. Among the seven cooling conditions, the conditions that included the
vest were the most effective in alleviating heat strain. Moreover, even in the case of wearing
scarf A with about 1% SAcooled a significant difference was found when compared to the case
without cooling. Heat storage was evaluated more specifically by PSI rather than by CI
(Figure 1).
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