POSSIBILITIES AND LIMITATIONS OF DIFFERENTIAL 

 BRAIN COOLING IN DOGS * 



JAY Af. JENSEN.t W. AI. PARKINS axd H. l\. VARS 



It is the paradox of hypothermia that hotli the i)romi.se and the liniitation of 

 the method He in the same direction. The central nervous system is protected Iw 

 cold against ischemia and, within certain limits, the measure of protection seems 

 to increase as the hypothermia deepens. The myocardium is endangered In- cold and 

 its vulnerahility to arrest and to arrhythmia seems to hecome greater as the tem- 

 perature falls. In the dog and in the human this riddle remains. If these phenomena 

 could he studied separately perhaps additional data might he ol)tained ahout both. 

 This was attempted by cooling the brain, the heart, and the body core somewhat 

 selectively. 



Procedure. The cooling .system consisted of an ice bath, a polyviii}-! coil, and 

 a pump. Adult, mongrel dogs were anesthetized with sodium pentobarbital. An 

 endotracheal tube was placed. The pump was adjusted to deliver through the coil 

 approximately 100 ml. of blood per minute. 



The carotid artery on one side was exposed and ligated. Polyvinyl catheters 

 were placed above and below the ligatures with the proximal catheter directed 

 toward the heart and the distal catheter directed toward the brain. The catheters 

 were connected to the coil so that oxygenated blood would be pumped from the 

 animal, through the polyvinyl coil immersed in ice, and pumped back into the 

 carotid and through the brain. Small holes were drilled into the skull and through 

 these copper-constantan thermocouples were inserted into the cortex of the frontal 

 lobes. Base line recordings were taken, the perfusion pump was started, and differ- 

 ential cooling of the animal was begun. 



Most of the animals were heparinized after completion of the operative pro- 

 cedures. In several instances, however, the heparin was inadvertently not given and 

 only rarely was there evidence of clotting within the coil. The temperature of the 

 blood entering the carotid artery from the iced coil ranged from 3° to 10° C. The 

 cooling period extended from 10 to 20 minutes. In certain of the animals the chest 

 was opened and the inflow tract was occluded. At the conclusion of the procedures 

 the animals were warmed in a warm water bath. 



The measurements shown on the accompanying graph were made during the 

 differential cooling of a dog. The rectal temperature is shown on the top line. 

 The brain temperatures were recorded on the perfused and on the unper fused sides. 

 These factors were recorded during 15 minutes of cooling, during 30 minutes of 

 complete occlusion of the general circulation, and during the immediate recoverv 

 period. This dog tolerated 30 minutes of complete occlusion of the superior and 

 inferior vena cava without evidence of damage of any kind (fig. 1 ) . 



Results. In 15 dogs the general circulation was completely interrupted by clamp- 

 ing the inflow tracts. The interval of occlusion varied from 15 to 40 nu'nutes. 



* This work was supported in part under contract between the Department of the Army and the 

 University of Pennsylvania. 



tU.S.P.H.S. Research Fellow of the National Heart Institute and a former Research Fellow 

 of the American Cancer Society. 



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