CORONARY FLOW— BERNE 



167 



6 8 



Minutes 



'■■' blood entering L. Circumflex Art. 



Fig. 3. — Effect of changing temperature of blood perfusing the left circumflex coronary 

 artery on coronary blood flow in a dog fibrillating-hcart preparation. Perfusion pressure was 

 kept relatively constant by a pump-perfusion system. 



coronary sinus blood than in the arterial blood. The average decrease of potassium in 

 coronary sinus blood in 11 experiments was 15 per cent. In the control periods in 

 which the left coronary inflow was kept at normal body temperature the coronary 

 sinus blood potassium concentration equaled that found in the arterial blood. In two 

 experiments in which the whole animal was cooled the potassium level in the cardiac 

 venous blood was below the arterial blood concentyati(jn. a finding similar to that of 

 Dr. Swan. 



Another interesting olxservation we made in this series of experiments was that 

 in seven out of eleven normothermic dogs ventricular fibrillation occurred when 

 blood entering the left coronary artery was cooled. 



The second type of experiment we did to shed some light on the factors influencing 

 coronary resistance in hypothermia was to make phasic flow meastirements in the 

 circumflex coronary artery of the dog in normothermia and hypothermia. At pres- 

 ent we have done only a few such experiments. The bristle flowmeter of Brecher 

 and Praglin was used to make these flow measurements. 



We were interested in finding out whether the prolonged period of isometric 

 relaxation that obtains in hypothermia restricts coronary blood flow. Figure 4 depicts 

 records of simultaneously recorded aortic, left ventricular, and left atrial pressure 

 curves in progressive hypothermia. In part A at a temperature of 40° C. isometric 

 relaxation is brief, 0.04 seconds, whereas in part H at 20.5° C. it occupies a signifi- 

 cant portion of the cardiac cycle, 0.52 seconds. However, in this experiment the 

 duration of systole increased from 0.18 to 1.00 seconds and the question is how 



