CORONARY BLOOD FLOW DURING HYPOTHERMIA 



R. M. BERNE 



Dr. D'Amato referred to our experiments in which we found that coronary blood 

 flow was fairly well maintained in the hypothermic state at a time when aortic pres- 

 sure had reached very low levels. This is illustrated in figure 1, where the coronary 

 blood flow is plotted against perfusion pressure (mean aortic pressure) during pro- 

 gressive hypothermia. At a temperature of 21° C. when perfusion pressure had 

 reached 42 mm. Hg. and coronary blood flow was 11 cc. per minute we elevated 

 perfusion pressure by means of a mechanical pump (line B) and observed that at 

 comparable pressures coronary blood flow was in excess of that noted during the 

 induction of hypothermia. We have extended these studies in an attempt to deter- 

 mine the cause of this lowered resistance in the coronary bed during hypothermia. 



Two types of experiments were carried out. In one we cooled the blood entering 

 the common left coronary artery or its circumflex branch and made observations on 

 flow, and in the other we made phasic coronary flow measurements in hypothermia. 

 Figure 2 depicts the efi^ect of alternately cooling and warming the blood perfusing 

 the left coronary artery in a dog with normal body temperature. From top to bottom, 

 we have perfusion pressure, coronary blood flow and the temperature of the blood 

 entering the circumflex branch of the left coronary artery, all plotted against time. 



O 



Q 

 O 



3 



< 



z 

 o 

 q: 

 O 

 o 



120 



100 



80 



60 



40 



20 



PERFUSION PRESSURE mm h& 



Fig. 1. — Effect of increasing coronary perfusion pressure in severe hypothermia. Curve A is 

 the pressure/flow curve in progressive hypothermia. Curve B represents the flows obtained at 

 blood temperature of 21° C. when perfusion pressure was artificially elevated. 



165 



