2007, Piran, Slovenia
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2007, Piran, Slovenia

2007, Piran, Slovenia 2007, Piran, Slovenia

lboro.ac.uk
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Environmental Ergonomics XII Igor B. Mekjavic, Stelios N. Kounalakis & Nigel A.S. Taylor (Eds.), © BIOMED, Ljubljana 2007 Experimental protocol: We modified the protocol of Mekjavic et al. (1996). Subjects donned a water perfused suit, comprised of three segments: trousers, shirt and hood (Figure 1). By perfusing the segments in parallel with water maintained at 25°C at a rate of 600 cc/min, mean skin temperature (Tsk) was maintained at 28°C. Following the recording of baseline values, subjects commenced exercising at 50% of their maximum work rate on a cycle ergometer. The exercise was terminated once the onset of sweating was observed, which occurred after 10-15 min of exercise. Thereafter, subjects remained seated on the ergometer for an additional 100 min. During this phase, the extraction of heat by water perfusing the suit initiated core cooling. Sweating abated, and eventually the shivering response was triggered. Figure 1. Diagram for the heating/cooling system. Measurements: Rectal (Tre) and skin (Tsk: arm, chest, thigh and calf) temperatures were monitored with thermistors and the values stored every ten seconds with a data logger system (Cadac2 model 9200A, Tokyo. Japan). Sweating rate was measured at the forehead with a sweat rate monitor (model SKD-4000, Skinos Co.). Oxygen uptake was monitored with a gas analyser (Respiromonitor RM-300i, Minato Med. Science, Co.). Maintenance of a normal skin temperature, while simultaneously extracting 120W/m 2 of heat was achieved by having subjects wear a Cool Tubesuit TM (Med-Eng Systems Inc., Ottawa, Ontario, Canada) water perfused suit. Water perfusing the suit was pumped at a rate of 600cc/min (Water Pump Model Super Tepcon, Terada, CITY, Japan) from a bath, in which the temperature of the water was maintained at 25 by a Cool Mate Model TE-105M heat exchanger (Toyo Seisakusho Co., CITY, Japan). Data Analysis: The boundaries of the zone where rectal temperatures coincided with the onset of shivering and sweating were determined. Whereas the onset of sweating is quite distinct, the shivering threshold was taken as the Tre, which coincided with a significant elevation in the oxygen above resting values. The sweating threshold was as the point at which sweating increased. Since we have demonstrated the experimental protocol with which to quantify the individual variability in the core and peripheral interthreshold zones (Kakitsuba et al. 2005), the main purpose of the present study was to examine whether non-thermal factors affect the interthreshold zones based on the data collected for the past three years. Correlation between the magnitudes of the interthreshold zone and non-thermal factors such as age, height, weight, body surface area, surface area-to mass ratio, adiposity and maximum work load in addition 250

Non-thermal factors to some categorized variables such as quality of sleep and sensitivity to the heat and cold was then confirmed. RESULTS AND DISCUSSION Example of the changes in Tre and mean skin temperature ( ,TSK) are indicated in Figure 2. During cooling periods, Tre decreased at a rate of 0.5°C per hour, which is about half that observed during water-immersion experiments (Mekjavic et al., 1991). Unfortunately, ,TSK could not be controlled consistently at 28°C due to indirect cooling with the water perfusing suit. It changed from 32°C during exercise to 30°C at the end of exposure. However, since the ,TSK changed in the same manner, regardless of subjects, the extent of its affect on the thresholds may be expected the same. Rectal temperature 38 37.5 37 36.5 36 35.5 Tr MST sweating threshold Null zone shivering threshold Exercise Subject B 0 20 40 60 80 100 120 140 160 time min Figure 2. An example of changes in rectal and mean skin temperatures during exercise and cool exposure with water perfusing suit. For some subjects, the threshold for shivering could not be identified clearly, since marked elevations of oxygen uptake were not observed. However, we could monitor a state that subjects started to regulate their body temperatures by increasing oxygen uptake. Based on the initial Tre, the temperature difference between the initial Tre and the threshold Tre was calculated, and these data are listed in Table 2. Since individual differences in Tre-sw and Tre-shivering can be observed, effects of non-thermal factors on those thermoregulatory responses were evaluated using the multiple regression analysis. The results indicated that the multiple regression equation may not be suitable for predicting the inter-threshold range. However, it was found that the magnitude of sensitivity to the cold (r=0.21), quality of sleep (r=0.26) and blood pressure (r=0.35) were relatively correlated with these ranges, as compared with other variables. As pointed by Mekjavic and Eiken (2006), these non-thermal factors are expected to be influential for estimation of the ranges. Table 2. Inter-threshold zone (n=32). Initial Tre Tre- Tre- Interthreshold range 40 38 36 34 32 30 28 26 24 22 20 Mean skin temperature 251

Non-thermal factors<br />

to some categorized variables such as quality of sleep and sensitivity to the heat and cold was<br />

then confirmed.<br />

RESULTS AND DISCUSSION<br />

Example of the changes in Tre and mean skin temperature ( ,TSK) are indicated in Figure 2.<br />

During cooling periods, Tre decreased at a rate of 0.5°C per hour, which is about half that<br />

observed during water-immersion experiments (Mekjavic et al., 1991). Unfortunately, ,TSK<br />

could not be controlled consistently at 28°C due to indirect cooling with the water perfusing<br />

suit. It changed from 32°C during exercise to 30°C at the end of exposure. However, since the<br />

,TSK changed in the same manner, regardless of subjects, the extent of its affect on the<br />

thresholds may be expected the same.<br />

Rectal temperature<br />

38<br />

37.5<br />

37<br />

36.5<br />

36<br />

35.5<br />

Tr MST<br />

sweating threshold<br />

Null zone<br />

shivering threshold<br />

Exercise<br />

Subject B<br />

0 20 40 60 80 100 120 140 160<br />

time min<br />

Figure 2. An example of changes in rectal and mean skin temperatures during exercise<br />

and cool exposure with water perfusing suit.<br />

For some subjects, the threshold for shivering could not be identified clearly, since marked<br />

elevations of oxygen uptake were not observed. However, we could monitor a state that<br />

subjects started to regulate their body temperatures by increasing oxygen uptake. Based on the<br />

initial Tre, the temperature difference between the initial Tre and the threshold Tre was<br />

calculated, and these data are listed in Table 2. Since individual differences in Tre-sw and<br />

Tre-shivering can be observed, effects of non-thermal factors on those thermoregulatory<br />

responses were evaluated using the multiple regression analysis. The results indicated that the<br />

multiple regression equation may not be suitable for predicting the inter-threshold range.<br />

However, it was found that the magnitude of sensitivity to the cold (r=0.21), quality of sleep<br />

(r=0.26) and blood pressure (r=0.35) were relatively correlated with these ranges, as<br />

compared with other variables. As pointed by Mekjavic and Eiken (2006), these non-thermal<br />

factors are expected to be influential for estimation of the ranges.<br />

Table 2. Inter-threshold zone (n=32).<br />

Initial Tre Tre- Tre- Interthreshold range<br />

40<br />

38<br />

36<br />

34<br />

32<br />

30<br />

28<br />

26<br />

24<br />

22<br />

20<br />

Mean skin temperature<br />

251

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