104 



PHYSIOLOGY OF INDUCED HYPOTHERMIA 



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J I I L. 



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Fig. 16. — Data of figure 15 plotted to test for an exponential relationship. Ordinate: logarithm 

 of the heart rate/min.; abscissa: reciprocal of the absohite body temperature. 



Chatfield and Lyman,'" who studied arousing hamsters electrocardiographically, 

 found that the rate of conduction over the auricle and through the A-V node (as 

 measured by the reciprocal of the P-R interval) also varied linearly with heart rate, 

 while the duration of the QRS complex shortened markedly as heart rate increased 

 (fig. 18). Accurate measurements of the latter were unfortunately precluded by the 

 filtering condensers necessary for minimizing the muscle action potentials and slow 

 base line shifts w^hich occurred in the unanaesthetized animal. Another change in the 

 electrocardiogram during arousal was an increase in the prominence of the T wave. 

 This was interpreted as indicating the development of unequal rates of repolariza- 

 tion in the two ventricles. In the human, however, an increase in amplitude of the 

 T waves is indicative of a high serum potassium^^* and the level of this ion in the 

 serum of arousing hamsters might well be investigated. As the process of arousal 

 progressed and the heart was Ideating more rapidly the P wave was seen to rise from 

 a base line displaced by the T wave. Thus late in the process of arousal, when the 

 heart attains extremely fast rates, another impulse must be transversing the auricles 

 even before the ventricles are completely repolarized. 



The rapid conduction of the cardiac impulse is interesting, for Walls^^^""' found 

 that there were no Purkinje fibers in the atria or the right ventricle of the hamster 

 heart, and only a limited number in the left ventricle. Thus the heart of the hamster 



