Heat loss from the heart in dogs

¹ Department of Physiology and Biophysics, University of Washington School of Medicine, Seattle, Washington

Thermistors were inserted into the coronary sinus and the root of the aorta in anesthetized dogs to record the temperature difference between the left ventricular coronary inflow and outflow. Coronary sinus flow was directly measured with an indwelling cannula. Heat loss from the coronary vasculature was then calculated as the product of the temperature gradient and the coronary sinus flow. The average temperature difference during control periods was about .5 C (range, .24–.88 C). Isoproterenol, l-epinephrine, and acetylstrophanthidin all increased the temperature gradient, the coronary sinus flow, and, therefore, the myocardial heat loss. A small but significant amount of heat was lost from the epicardial surface of the left ventricle to the lungs in the closed-chest dog. Direct physical measurements of heat loss avoid many of the uncertainties inherent in estimates of wasted energy based on the energy equivalent of myocardial oxygen consumption.