HIBERNATION IN MAAfAfALS— LYMAN and CIIATFIELD 93 



their CO2 tensions were abnormally high. Using golden hamsters and ground squir- 

 rels, Lyman and Hastings"-^ concluded that the total CO2 was indeed higher during 

 hibernation but the pCOa was lower. The total CO2 in these experiments was not as 

 high comparatively as that found by previous investigators but this was probably 

 due to the extremely high total CO^ in the anaesthetized controls. Bicarbonate and 

 pH were essentially the same in hibernating and awake hamsters but the pH was 

 somewhat lower in hibernating ground squirrels. 



Recalculation of the data of Endres^^ and of Stormont, ct al.,''- showed that their 

 results were similar except for the high blood CO2 tension in Stormont's observa- 

 tions which disagreed with their own data on tissue gas pockets (table II). Lyman 

 and Hastings^^ concluded that there was no evidence that the sensitivity of the 

 respiratory center was depressed during hibernation, other than the observed fact 

 that there was a larger range of variation in the acid-base balance of the hibernat- 

 ing animals. In a companion paper, Lyman"^ showed that hibernating hamsters and 

 ground squirrels responded to an increase of the inspired CO2 by an increase in 

 respiratory rate with about the same sensitivity as normal human beings (fig. 9). 

 Ground squirrels, hamsters and probably all other hibernators have long periods of 

 apnoea followed by several respirations. The apnoea could be abolished by high 

 concentrations of CO2. Popovic^'' has shown that the hibernating European ground 

 squirrel is also sensitive to lowering of the O2 tension and that this animal responds 

 to the lack of Oo during hibernation in a manner similar to that of the animal when 

 awake. 



The work of Rasmussen,^° Endres^' and McBirnie, ct al..^^ indicates that the 

 blood of the woodchuck is very similar to other mammalian bloods in its O2 com- 

 bining power. In view of the great reduction in the rate of Oo consumption during 

 hibernation, the gradient of Oo tension from blood to tissues presumably would 

 need to be much less than in active animals. The displacement of the O2 dissociation 

 curve to the left^® as the result of lowered temperature means that a lower Oo ten- 

 sion is required for the dissociation of oxyhemoglobin. However, since the percent- 

 age saturation of hemoglobin in venous blood of animals in hibernation is not essen- 



TABLE II 

 Average Data Found by Different Authors for Plasma pH and CO2 



Species 



Hamsters " 13 



Ground squirrels " . 

 European hamsters 

 Ground squirrels " 

 Ground squirrels " 



* Lyman and Hastings (1951). 

 •> Awake in cold. 



<^ Endres (1924). 



"* pH values were calculated. 



« Stormont ct al. (1939). 



* pH values were corrected to temperature of the animal, 

 s Awake in cold, no water. 



