244 PHYSIOLOGY OF INDUCED HYPOTHERMIA 



TABLE I 



Minimal Temperatures (Rectal) for Selected Reflexes and Other Reactions as 

 Obser\t.d in the Rew arming Period of the Cat 



(From Simpson and Britton) 



Knee jerk persisted to 16° C. 



Respiratory reflex to pain persisted to 16° C. 



Ankle jerk recovered at 17° C. 



Flexor withdrawal recovered at 20° C. 



Spontaneous stepping motion recovered at 20° C. 



Micturition reflex to pain recovered at 16-24° C. 



Phonation to pain recovered at 20° C. 



Pinna reflexes recovered at 20° C. 



Clawing recovered at 21.5° C. 



Blinking reflex recovered at 21.5° C. 



Corneal reflex recovered at 22° C. 



Light reflex recovered at 22-24° C. 



Phonation, spontaneous recovered at 22° C. 



Swallowing and sneezing recovered at 22° C. 



Licking recovered at 25° C. 



Vomiting recovered at 26° C. 



Audition recovered at 27.5° C. 



Vision recovered at 27-28° C. 



Olfaction recovered at 27.5° C. 



Voluntary movements recovered at 26-27° C. 



Coordinated movements recovered at 30° C. 



The patient becomes dysarthric in this range and begins to lose contact with his 

 surroundings, although pain is readily appreciated. However, in the 30° C. range 

 some patients can recognize relatives and other persons familiar to them. At about 

 27° C. they are unable to respond to verbal stimuli and voluntary motion is lost. 

 The pupillary light reaction, deep tendon reflexes, superficial skin responses and the 

 gag reflex are lost at a level of 25° to 26° C. Because of the limitation imposed 

 by cardiac dysrhythmias at lower temperatures on homeothermic animals, the cere- 

 bral response to cooling in the range 8°- 18° C. was not readily appreciated until 

 the work of Jensen and Parkins.-" They differentially cooled the brain to tempera- 

 tures of 8°- 12° C. in nine dogs, noting gross neurological damage in seven dogs 

 and fatal cardiac arrhythmias in two. However, in seven dogs cooled only to the 

 range of brain temperatures of 12°- 18° C, neurological abnormalities were not 

 observed. 



In summary, above the common level for ventricular fibrillation, Simpson demon- 

 strated the absence of gross damage to the central nervous system and the presence 

 of a state of narcosis for at least a period of several hours. Below this level, Jensen 

 and Parkins have found definite and presimiably irreversible injury. Unfortunately 

 the specific temperatures and exposure times for such injury have not been deter- 

 mined. 



Peripheral nerve. Forbes and Ray, in their classical paper in 1923," established 

 the preservation of excised mammalian nerve function to a level of about 8° C. 

 They showed that the siu'vival period of these nerves varied inversely with the 

 temperature, and thus provided a routine laboratory method of nerve preservation. 



