CARDIOVASCULAR FUNCTIONS— D'AMATO 155 



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DISCUSSION 



Dr. I. K. R. McMillan: I would like to start by saying that our group in England 

 a year or two ago did a similar experiment on calcium [unpublished]. I am delighted 

 to see our results agreed so closely. In fact, I would carry it a little further. By 

 watching the EKG we could give calcium chloride and produce an ST elevation at 

 temperatures where it does not normally appear (i.e., 28° C). If we did it the other 

 way around, and gave more potassium or alternately sodium acid phosphate and 

 mopped up the free calcium ions at a temperature of 25° C. we could remove that 

 elevation entirely and cool the dog several degrees further before it started to 

 reappear. We have also been interested in the hemodynamics of the cold heart, and 

 Dr. Case, Dr. Stainsby and I have been trying to quantitate the function of the cold 

 ventricle along the lines of the work previously published by Dr. Sarnoff and his 

 associates. In view of the diminution in cardiac output, coronary flow, and aortic 

 pressure during hypothermia, it seemed desirable to examine the contractility of 

 the myocardium in this state. The amount of work per stroke that the heart is able 

 to deliver at any given filling pressure is a measure of its contractility, and is best 

 expressed by ventricular function curves, as described by Sarnoff, Berglund and 

 Case.^' - For the determination of these curves, continuous, simultaneous recordings 

 were made of cardiac output, left main coronary artery flow, aortic pressure, pul- 

 monary artery pressure, and right and left atrial pressures. Myocardial work was 

 increased Ijy intermittent intravenous transfusion of blood until the work reached a 

 maximum. Curves of filling pressure against stroke work were plotted for each 

 ventricle at Z7° C. and 28° C. All dogs were under morphine-chloralose-urethane 

 anesthesia and positive pressure breathing. Blood was cooled by passage from the 

 femoral artery to the femoral vein through a coil immersed in ice water." 



Values of the important hemodynamic variables as cooling progressed are shown 

 in figure 1. The rise in filling pressures during cooling reported by other workers 

 did not occur in these experiments. 



Figure 2 shows a plot of left ventricular stroke work against mean left atrial 

 pressure at 2>7° C. and 28° C. It will l)e noted that the stroke work generated per 

 unit of filling pressure in the cold heart was about the same as that of the warm 

 heart, suggesting that the contractility at the two temperatures was the same. How- 

 ever, present work in this laboratory indicates that the function curve is elevated 

 progressively at normal temperatures as heart rate decreases. During these curves, 



