Although the environmental stresses to which man is subjected on the ground are less than those commonly encountered in aviation or under water, they may still exceed an individual's powers of adaptation. Extremes of temperature, commonly encountered in the Arctic or the tropics, may occur in regions of normally temperate climate and lead to failure of temperature regulation, resulting in hypothermia, frostbite, heat exhaustion, or heat stroke. High mountains impose additional hazards due to high winds and lack of oxygen, and deep mines are dangerous work-places because of high temperature and humidity. Some physiological acclimatization occurs in extreme natural environments and the dangers may be reduced by appropriate clothing, diet and behaviour.
The adjustment of sleep-wake patterns and the circadian temperature rhythm was monitored in nine Royal Norwegian Air-force volunteers operating P-3 aircraft during a westward training deployment across nine time zones. Subjects recorded all sleep and nap times, rated nightly sleep quality, and completed personality inventories. Rectal temperature, heart rate, and wrist activity were continuously monitored. Adjustment was slower after the return eastward flight than after the outbound westward flight. The eastward flight produced slower readjustment of sleep timing to local time and greater interindividual variability in the patterns of adjustment of sleep and temperature. One subject apparently exhibited resynchronization by partition, with the temperature rhythm undergoing the reciprocal 15-h delay. In contrast, average heart rates during sleep were significantly elevated only after westward flight. Interindividual differences in adjustment of the temperature rhythm were correlated with some of the personality measures. Larger phase delays in the overall temperature waveform (as measured on the 5th day after westward flight) were exhibited by extraverts, and less consistently by evening types.
Siberian lemmings seem to have lesser noradrenaline (NA) calorigenic action and higher beta-adrenergic "asymmetry" of catecholamine calorigenic effects than the cold- and warmth-adapted laboratory rodents. Selective inhibition of catecholamine effects by beta-adrenoblocking drug propranolol, obvious potentiation of NA effect by caffeine, and compensatory increasing of thermoregulatory musclar contractile activity during the blockade of betaadrenoreceptors under cooling suggest the domineering of betaadrenergic mechanisms of thermogenesis in siberian lemmings and their high thermoregulatory lability.
The effect of chronic ethanol intake and warm acclimation on the heat tolerance of rats under the influence of alcohol was studied. The animals were divided into two groups: Group 1 received water as their fluid intake and, group 2 received a 10% ethanol solution, and both groups were exposed to a temperature of 30 degrees C for 4 weeks. Excretion of urinary catecholamines was measured prior to warm exposure at 22 degrees C and once a week during warm exposure at 30 degrees C. After warm acclimation a dose of alcohol 2 g/kg was injected in the rats intraperitoneally (i.p.), and then they were exposed to a heat stress of 40 degrees C for 45 min. During warm acclimation, the controls consumed more fluid and they excreted more norepinephrine into the urine than the alcohol-fed animals during the first week. After the period of acclimation there were no significant differences in urinary excretion of catecholamines between the groups. Colonic temperature of the controls was 0.7 degrees C higher than in the alcohol-fed animals. Acute alcohol administration (2 g/kg) increased the colonic temperature of the alcohol-fed animals during a heat stress of 40 degrees C more than in the controls. After heat stress, the concentration of catecholamines in the blood was significantly higher in the controls. The results show that the hyperthermic effect of ethanol was more considerable in the rats whose drinking water during warm acclimation was an ethanol solution.
Anterior chamber depth is an inheritable trait which is affected by age, gender and race. Over 30 years ago, Alsbirk proposed that the shallow anterior chamber, which was typical of the Greenlandic Inuit, and which brings the iris in proximity to the cornea, may have evolved as a thermoregulatory adaptation to resist corneal freezing. Here, this hypothesis is revisited. Recent population genetic data which provide evidence for migration patterns of early humans are discussed and the notions of natural selection and ocular adaptation to cold climates are considered. Problems with the hypothesis are examined, but the idea that the shallow anterior chamber has a thermoregulatory role appears sound and suggests that shallow anterior chambers may have evolved in Homo sapiens living in north-east Asia during the last Ice Age.
The evaluation of cold stress in working life was done in 13, mainly outdoor, occupations and 143 workers using local temperatures, body cooling and thermal sensations. The subjects in the study were young, healthy men and they wore the type of winter clothing generally used in those ambient temperatures (+6...-29 degrees C), for in a work load of from 112 to 480 W. Local temperatures on finger skin indicated that manual dexterity was often reduced in outdoor work. A risk of frostbite was frequently found on the cheek and the wind chill index predicted the risk quite well. Body cooling was often temporarily too high when measured by heat debt and mean skin temperature. Thermal sensations were cool or cold occasionally in 28% of the workers interviewed. The insulation of clothing worn was often lower than the IREQmin-value recommends. The results showed that in outdoor work in winter time cold stress frequently reduced (70%) working ability at least for a short period. Mean skin temperature seems to be, in practice, a useful indicator for body cooling and the IREQmin-value was suitable, especially in light work, to indicate body cooling. A very sensitive factor for the expression of cold stress was finger temperature, at least as an indicator of finger dexterity. Due to the adverse health effects found the cold stress should also be evaluated more systematically in occupational health and safety with health examinations, with protective clothing and technical preventive means.
Leatherback turtles in the Northwest Atlantic Ocean have a broad geographic range that extends from nesting beaches near the equator to seasonal foraging grounds as far north as Canada. The ability of leatherbacks to maintain core body temperature (Tb) higher than that of the surrounding water is thought to be a key element of their biology that permits them to exploit productive waters at high latitudes. We provide the first recordings of Tb from freely swimming leatherbacks at a northern foraging ground, and use these data to assess the importance of behavioral adjustments and metabolic sources of heat for maintenance of the thermal gradient (Tg). The mean Tb for individual leatherbacks ranged from 25.4 ± 1.7 to 27.3 ± 0.3 °C, and Tg ranged from 10.7 ± 2.4 to 12.1 ± 1.7 °C. Variation in mean Tb was best explained by the amount of time that turtles spent in the relatively warm surface waters. A diel trend in Tb was apparent, with daytime cooling suggestive of prey ingestion and night-time warming attributable to endogenous heat production. We estimate that metabolic rates necessary to support the observed Tg are ~3 times higher than resting metabolic rate, and that specific dynamic action is an important source of heat for foraging leatherbacks.