PHYSIOLOGICAL EFFECTS OF COLD ENVIRONMENTS ON MAN 



Dr O. G. Edholm 

 (London) 



The problem of mammalian, including human life in cold environments is essen- 

 tially a problem of insulation. Warm blooded animals, apart from periods of hiber- 

 nation, maintain a relatively constant deep body temperature of approximately 37°C 

 with an outer shell of tissue, the temperature of which depends on the thermal en- 

 vironment and the state of activity of the animal. The constancy of the internal 

 temperature depends on a balance of heat output and heat loss. Scholander, Irving 

 and their colleagues, who have recently published an important series of studies on 

 arctic animals, point out that there are three ways by which such animals might 

 develop mechanisms for survival in extreme cold. There might be a fluctuating deep 

 body temperature, varying according to external temperature. Their evidence strongly 

 discounts such a possibility: arctic animals, such as the fox or the dog, maintain a 

 constant deep body temperature of the same order as temperatures found in animals 

 inhabiting temperate or tropical 2»nes. There could be an increased heat production, 

 i.e. a high metabolic rate. Scholander and Irving do not consider that that is an im- 

 portant factor as the basal or resting metabolic rates in a large variety of arctic ani- 

 mals showed the same relationship to surface area as demonstrated by animals living 

 in tropical or temperate 2ones. The points fall close to the 'mouse- elephant curve' 

 constructed by Benedict many years ago . 



The third mechanism consists of variatidn of the insulation of the deep body 

 temperature. This in turn depends on the thickness of the subcutaneous layer of 

 fat, the rate of blood flow in the skin and superficial tissues, the rate of production 

 of water on the surface of the body, and the thickness of the fur. In their experience 

 Scholander and Irving found that maintenance of a constant deep body temperature in 

 arctic animals depended essentially on adequate insulation, and this in turn was 

 largely due to the thickness of the layer of fur. 



How does man adjust physiologically to life in cold environments? Is there any 

 evidence of relatively long term effects which suggest acclimatization to cold? It 

 should be made clear, at the outset, that the evidence so far is meagre, and there is 

 certainly no such dramatic effects as are observed when man is exposed to hot en- 

 vironments, as described by Dr Weiner. 



The critical temperature for a nude man at rest is relatively high, about 27°C. 

 That means that body temperature is maintained without any change in metabolism, 

 down to temperatures of 27°C. Thereafter any further fall of environmental tempera- 

 ture will stimulate a'n increased metabolism. This may be compared with a critical 

 temperature of — 40°C for the arctic fox. 



Metabolic rate, i.e. heat production or oxygen consumption, starts to increase 

 when the environmental temperature falls below the critical temperature. The in- 

 creased heat production is largely or possibly entirely due to shivering or other mus- 

 cular activity. The rise in metabolic rate may be very considerable and for short 

 periods can be as high as 6-7 times the resting or basal metabolic rate, i.e. up to 



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