Changes in cold tolerance due to a 14-day stay in the Canadian Arctic.

Response to cold exposure tests both locally and of the whole body were examined in subjects who stayed in the arctic (average maximum and minimum temperatures -11 and -21 degrees C respectively) for 14 days of skiing and sleeping in tents. These changes were compared to responses in subjects living working in Ottawa, Canada (average max. and min. temperatures -5 and -11 degrees C respectively). The tests were done before the stay in the Arctic (Pre), immediately after the return (Post 1) and approximately 32 days after the return (Post 2). For the whole-body cold exposure each subject, wearing only shorts and lying on a rope mesh cot, was exposed to an ambient temperature of 10 degrees C. There was no consistent response in the changes of metabolic or body temperature to this exposure in either of groups and, in addition, the changes over time were variable. Cold induced vasodilatation (CIVD) was determined by measuring temperature changes in the middle finger of the nondominant hand upon immersion in ice water for 30 min. CIVD was depressed after the Arctic exposure whilst during the Post 2 testing, although variable, did not return to the Pre values; the responses of the control group were similar. These results indicate that normal seasonal changes may be as important in adaptation as a stay in the Arctic. Caution is advised in the separation of seasonal effects when examining the changes in adaptation after exposure to a cold environment.

Heat loss caused by cooling the feet.

The effect of cooling the feet to alleviate heat strain was examined. Subjects, wearing chemical protective clothing, immersed their feet in water at temperatures of 10, 15, 20, 25, and 30 degrees C after sitting for 120 min at 35 degrees C. Heat lost via the feet ranged from 151 +/- 15 to 55 +/- 5 W, being greater in the colder water. In a second experiment, subjects wearing chemical protective clothing and specially designed water-cooled socks walked on a treadmill at 5 km.h-1 and 2.5% grade for 90 min at 35 degrees C. Four conditions were examined: no cooling, cooling throughout the walk, cooling during the last 60 min, and cooling during the first 30 min. Rectal and skin temperatures and heart rates were monitored. Cooling for the first 30 min had little effect on the measured parameters, however, when core temperatures rose to over 37.5 degrees C, cooling during the last 60 min significantly attenuated the increase in body temperatures and heart rates. We conclude that this method could be used to alleviate heat strain.

Effect of working in hot environments on respiratory air temperatures.

The purpose of this study was to obtain an accurate measure of the temperature of respired air of subjects working on a treadmill at various ambient temperatures and ambient relative humidities (RH). The experiments were conducted in an environmental chamber at each of four different ambient temperatures (nominally 20, 30, 40 and 45 degrees C) and at two different ambient RH (20% and 100%) for a total of eight different conditions. Each experiment consisted of four tests at each ambient condition, these being: (A) standing quietly; (B) walking on a treadmill at 3 km.h-1, 0% grade; (C) walking on a treadmill at 3 km.h-1, 5% grade; and (D) walking on a treadmill at 5 km.h-1, 5% grade. It was found that under these conditions the maximum temperature of the expired air is independent of work rate and also ventilation rate but varies significantly with both the temperature and humidity of the inspired air. At low ambient RH the expired air temperature was [mean (SD)] 31.2 (1.3), 33.3 (0.7), 34.0 (1.7) and 35.6 (0.7) degrees C for ambient temperatures of 20, 30, 40 and 45 degrees C, respectively. At high ambient RH the expired air temperature was 32.0 (1.8), 35.3 (0.5), 37.6 (1.2) and 41.8 (0.8) degrees C at ambient temperatures of 20, 30, 40 and 45 degrees C, respectively. Thus the expired air temperature was higher at the higher ambient temperatures and ambient RH. While similar results have been reported before, the techniques used in this study should provide a more accurate measure of these effects than those previously reported.

Body composition and skin temperature variation.

Temperature variations near four common torso skin temperature sites were measured on 17 lightly clad subjects exposed to ambient temperatures of 28, 23, and 18 degrees C. Although variations in skin temperature exceeding 7 degrees C over a distance of 5 cm were observed on individuals, the mean magnitude of these variations was 2-3 degrees C under the coolest condition and less at the warmer temperatures. There was no correlation between the temperature variation and skinfold thickness at a site or with estimations of whole body fat content. These findings imply that errors in mean skin temperature measurement could arise from probe mislocation and/or subcutaneous fat distribution and that the problem becomes more acute with increasing cold stress. However, the magnitudes of these errors cannot be easily predicted from common anthropometric measurements.

Respiratory heat loss during work at various ambient temperatures.

The purpose of this investigation was to establish the temperature and humidity of the expired air of subjects working at various metabolic rates at ambient temperatures between -40 degrees C and 20 degrees C in order to calculate respiratory heat loss. Measurements of the respired air temperature and water vapour content were made for five subjects while they either stood or walked on a treadmill. The results indicated that the maximum respired air temperature varied slightly with the ambient air temperature but changes in metabolic rate, respiration rate and breathing frequency had no apparent effect on the expired air temperature under the conditions studied. The relative humidity of the respired air was found to be close to saturation in the extreme-cold environments. Heat loss due to respiration was between 25 and 30% of the resting metabolic and between 15 and 20% of the working metabolic rate.

Heat loss caused by immersing the hands in water.

The effect of immersing the hands up to the wrist in cold water to alleviate heat strain was examined in volunteers wearing chemical protective clothing and gloves. Each subject, who was monitored with skin and rectal thermistors, was observed while walking on a treadmill at two different work rates (283 +/- 47 and 455 +/- 58 watts) at 23 degrees C and at a resting state at 35 degrees C. After 20 min of work at 23 degrees C or after 120 min in the hot room, the hands were immersed in water at temperatures of 10, 15, 20, 25, and 30 degrees C. The amount of heat lost via the hands ranged between 124 +/- 14 and 31 +/- 4 watts (W) and was greater, the colder the water and harder the work. In most cases, this amount of cooling was sufficient to decrease skin temperature and lower the rate of increase of core temperature. We concluded that this method may be used to decrease resting time when working in the heat.

Measurement of torso skin temperature under clothing.

The influence of clothing on skin temperature distributions of the torso was investigated during and after cold exposure. Volunteers were cooled for one hour at 5 degrees C while wearing clothing designed to have insulation which was intended to be relatively uniformly distributed. Three different thicknesses of clothing were used. Following thermistor measurements of skin temperatures during the cold exposures, clothing was quickly removed from the upper parts of the body to enable thermographic investigations of the temperature distributions of the front of the bare torso. The evolution of temperature distributions were then studied at different ambient temperatures (5 degrees C and 20 degrees C) as a function of the thickness of the insulation which had previously been worn. The patterns of the temperature distributions, and the range and standard deviation of torso temperatures were all found to be relatively constant in spite of the different thicknesses of clothing worn or in the time-variant mean torso temperatures which resulted. The front torso sites normally used for the determination of mean skin temperatures were found to be on portions of the torso which were cooler than the surrounding regions. It was concluded that a site midway between the umbilicus and a nipple yields a more accurate estimate of mean torso temperature in the conditions of the present study.

A thermographic study of the effect of body composition and ambient temperature on the accuracy of mean skin temperature calculations.

The problem associated with using measurements from a small number of sites to determine mean skin temperature was investigated by studying variations in distributions of skin temperatures of the bare torsos of humans exposed to ambient temperatures of 18, 23, and 28 degrees C. Following a 60 minute equilibration period the temperatures of four regions (chest, abdomen, upper back, and lower back) were measured using both thermistors and an infra-red thermographic system. Regions of the torso usually represented by a single temperature exhibited significant point-to-point temperature variations especially in chilled subjects. Also an earlier finding was confirmed: in that larger variations in skin temperature distributions occur as body fat content increases. Caution must therefore be used in applying the concept of a mean skin temperature derived from a few select sites, especially with nude subjects who are chilled or have a high body fat content.