Myocardial oxygen consumption and coronary blood flow in hypothermia

¹ Cardiovascular Department, Medical Research Institute, Michael Reese Hospital, Chicago, Illinois

Effects of hypothermia (at 32° and 27°C) were determined in the open-chest anesthetized dog prepared for measurement of total coronary flow and myocardial oxygen consumption. When hypothermia was induced at any fixed cardiac output, cardiac oxygen consumption and heart rate declined while blood pressure remained constant. Cardiac external mechanical efficiency increased at the same time. Hypothermia did not alter the relationship between the myocardial oxygen requirement and the total cardiac effort as indicated by the product of blood pressure times heart rate. Without regard to the large individual variability, the coronary venous O₂ rose; thus the general trend during the induction of hypothermia was a decline in the coronary A-V oxygen difference, the percentage O₂ extracted by the heart and the ratio: cardiac O₂ consumption/O₂ availability. The coronary venous O₂ content and the coronary A-V O₂ difference remained fairly constant as the cardiac effort and its oxygen requirement varied during hypothermia, just as in the control period. Thus coronary flow was the only means of adjusting to the altered cardiac oxygen need in both periods.

Note:
With the Assistance of E. Boyd

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