106 



PHYSIOLOGY OF INDUCED HYPOTHERMIA 



can function at extremely high rates while having very little specialized conducting 

 tissue. 



Injection of the sympatheticolytic drug veratrosine (veratramine glucoside) 

 causes slowing of the heart of the waking hamster. On the other hand, the heart of 

 the normal waking animal is not accelerated further by injected epinephrine. There- 

 fore, Chatfield and Lyman'" concluded that the heart during arousal was being 

 driven at its maximum rate by the sympathetico-adrenal system. 



Changes in blood pressure. Chatfield and Lyman^° cannulated the carotid artery 

 of hibernating hamsters and recorded the blood pressure with a condenser manome- 

 ter. Although no record was made until at least 20 minutes after the hibernator was 

 first disturbed, it was apparent that blood pressure was initially low. The initial 

 measurement they obtained was on the order of 72/40, the mean pressure being 

 52 mm. of mercury. By the time the heart reached a rate of 100 beats per minute, 

 the blood pressure reached a normal level. It was noted in these experiments that the 

 pulse pressure increased transiently and then declined as the heart rate increased 

 further (fig. 19). 



Sources of heat. Dubois'^- in his pioneer monograph on hibernation in the marmot 

 concluded that the liver was the original source of heat in the waking animal, with 

 contraction of the diaphragm l^eing second in importance. Pembrey,^^*^ however, 

 felt that shivering was of paramount importance, while Johnson"^ favored contrac- 

 tion of the heart and respiratory muscles in the ground squirrel. Lyman and Chat- 



120 - 



100 



Blood 



80 

 Pressure 



mm. Hg 



60 



40 



20 



'Systolic 



I 1 I I 



I I I I ■ I ■ I I ■ I 



I 1 I I I I I I I 



' I ' ' I I 



50 100 150 200 250 



Heart Rate/min. 



300 



350 



400 



Fig. 19.— Systolic, diastolic, and mean hluud pressures of a typical arousing animal plotted 

 against heart rate, showing that hlood ])ressurc reaches high values long before the heart is 

 beating at its maximal rate. Presstn-es were obtained with a condenser nianonieter which elec- 

 trically integrates systolic and diastolic pressures to give the mean pressure. 



