MYOCARDIAL IRRITABILITY— HEGNAUER and COVINO 



341 



respiration in uur experiments, and in all of them we have had to struggle to avoid 

 respiratory alkalosis rather than respiratory acidosis. 



Dr. Niazi started his work in rats and showed that he could reduce their tem- 

 perature to about 15° C. before cardiac standstill occurred. Rather than discard 

 these rats after the heart had stopped he tried to revive them and found that he 

 was almost uniformly successful in doing so. Because his experiments were so 

 promising, we Ijought him a much more efficient respirator ; and with this respirator, 

 he lost all his rats. When he used 5 per cent carbon dioxide in oxygen rather than 

 oxygen alone with the more efficient respirator, he was able to save most of them. 



The change in pH that occurred in dogs respired with this respirator during cool- 

 ing are shown in figures 1 and 2. With oxygen alone the pH rose to high levels, but 

 it remained relatively constant at levels slightly below normal when 5 per cent car- 

 bon dioxide was used. 



The efficacy of using carbon dioxide during cooling is shown in two ways. First, 

 animals have been cooled to levels below 10° C. without ventricular fibrillation ; and 

 second, there appears to have been a reduced tendency to ventricular fibrillation 

 when operating on the cold heart. 



40 30 20 10 (0 20 30 



TEMP.°C COOLING REWARMING 



Fig. 1. — Changes in blood pH while cooling dogs which were breathing oxygen with an artificial 

 respirator. (By permission of Surgery, Gynecology and Obstetrics.) 



