88 PHYSIOLOGY OF INDUCED HYPOTHERMIA 



that the decline in metaboHc rate is the cause of the dechne in body temperatures J 



IN HIBERNATION 



Temperature. With the exception of bats, all hibernators curl in a tight ball dur- 

 ing hibernation with the hair erect, the head beneath the tail and the tail usually 

 curled around the body. This position permits a minimum of heat loss. 



The body temperature of the hibernating animal is reported by Johnson,^^ Kay- 

 ser^'^ and others to be 0.5 to 3° C. above the environmental temperature, but Lyman" 

 found it was less than 0.5° C. above that of the environment in the golden hamster. 

 Within a limited range, the body temperature passively follows the environmental 

 temperature."^' ^'^' ^' Unless the environmental temperature changes very slowly there 

 is always a lag between the body temperature and that of the environment, and many 

 of the reported observations of body temperature either well above or below the 

 environment are apparently due to a disregard of this lag. 



Circulation. All investigators agree that the heart rate is remarkably slow dur- 

 ing hibernation. Thus Hiebel and Kayser"^ report rates of two to three beats/minute 

 in European ground squirrels and marmots ; Suomalainen and Sarajas*'^ observed a 

 mean rate of 21 /minute in the hedgehog, and Chatfield and Lyman''^ reported rates 



HIBERNATING HEDGEHOG EXP 327 



Fig. 4. — Hedgehog. The animal enters, remains in, and comes out of hibernation three and 

 one half times in six days. Tf = anterior thermocouple; Tr = posterior thermocouple. (From 

 Dawe and Morrison, 1955.) 



§ A. R. Dawe and P. R. Morrison (Am. Heart J. 49: 367, 1955) have been able to study the 

 EKG in hedgehogs and two species of ground squirrels (Citellus parryi and Cifellus franklini) 

 as the animals entered hibernation. One of their graphs indicates that there is a decline in heart 

 rate prior to tlie drop in body temperature, but the senior author informs us that he is not 

 convinced that this has been firmly established (fig. 4). They found the relationship of heart 

 rate to body temperature very different in animals entering into and arousing from hibernation 

 (fig. 5). When entering into hibernation, the heart rate falls rapidly with the decline in body 

 temperature to about 20° C. At temperatures below this, the decline in heart rate in relation to 

 i)ody temperature is much slower. They point out that this indicates a hyperirritability of the 

 heart of animals which hibernate compared to non-hibernating mammals. A previous study by 

 H. S. S. Sarajas (Acta Physiol. Scand. 32:2^, 1954) also demonstrated a similar difference in 

 the relationship of heart rate and temperature in hedgehogs waking from hibernation and in 

 hedgehogs cooling in "artificial hibernation" after injection oi insulin. 



