74 



PHYSIOLOGY OF INDUCED HYPOTHERMIA 



PRE-OPERATIVE 



38 36 34 32 30 



DEEP COLONIC TEM PERATURE °C 



Fig. 11. — Relationship of tubular maxima for para-aminohippurate to deep colonic tempera- 

 ture in four partially poikilothermic dogs. The variation in slope may be related to retained 

 resistance to hypothermia; note that the line drawn through the solid circles approaches a 

 straight line and this animal retained the least cold combatting powers. 



and several unoperated animals when under a surgical depth of nembutal anesthesia. 

 Hypothermia was induced by subjecting the animals to an ambient temperature of 

 15 to 10° C. ; rewarming was accomplished by rapidly increasing the temperature of 

 the room to 40 to 45° C. All the unanesthetized dogs retained some ability to resist 

 hypothermia btit not sufficient in magnitude to prevent a progressive hypothermia 

 from developing when the cold exposure was sufficiently prolonged. 



The electrocardiograms have shown the expected P-R and Q-T prolongation, with 

 a broadened QRS, on cooling the poikilotherms. Additionally, the ST segment cur- 

 rent of injury has been noted when the deep colonic temperattu-e dropped 

 below 33° C. 



The pf)ikil(ithcrniic dogs have uniforniK- c\liil)ite(l a pi)sti)pcrati\e bracKcardia 

 and sinus arrhythmia with marked fluctuation in systolic and diastolic blood pressure 

 levels, depending on the respiratory phase. On cooling, a gradual reduction of the 



