MYOCARDIAL IRRITABILITY— ITEGNAUER axd COYIXO 

 1. BEFORE OCCLUSION 



347 



I0:08 30* c. 



2. CLAMPING OF AORTA 



10.36 2S* C. 



li:09 2 6' c 



3. AORTIC CLAMP OFF 



I0:50 24* C 



5. AFTER PERFUSION 



l##*^*^|iffiSaE] 



12:15 29* C. 



Fig. 4. — Prolonged clamping of aorta and pulmonary artery in hypothermic dogs hy 



blood cooling. 



6 5 4 3 2 1 ^- MINUTES 



Fig. 5. — Myocardial oxygen tension after coronary occlusion (26° C, extracorporeal oxygenation). 



recorded. On release of the aorta the heart goes into arrest which is prohably dne 

 to release of potassinm into the coronary vascular bed and after a minute of per- 

 fusion with oxygenated blood the heart starts to beat again. Such periods of com- 

 plete coronary occlusion can be repeated at will and in one experiment the myo- 

 cardium was subjected to three consecutive occlusions of 20 minutes each at 24° C. 

 After each occlusion the oxygen tension rose in 1 to 2 minutes to its original level 

 and the heart could tolerate again another prolonged period of ischemia. If the 

 aorta was occluded before the oxygen tension had returned to normal, ventricular 

 fibrillation developed winch did not respond to electric shock. 



The clinical applications of this remarkable ischemic tolerance of hearts perfused 

 with oxygenated cooled blood in the surgical repair of initral and aortic disease is 

 evident. 



Dr. A. Riberl (with H. B. Shumacker ) : In 1954 a brief note appeared in the 

 foreign letters section of the J. A.M. A. stating that Lian and his associates found 



