Temperature Gradients in the Hypothermic Dog

¹ From the Department of Physiology and the Cardiovascular Laboratory, College of Medicine, State University of Iowa, Iowa City, Iowa

Temperature gradients have been studied in 15 dogs subjected to hypothermia. In six of these experiments it was possible to maintain the rectal temperatures at approximately 25°C for from 4.5–34 hours. The results obtained indicate that there was little extraction of heat from the skin during progressive hypothermia. Initially the greatest amount of heat lost to the environment was from the muscular tissue. As the hypothermia progressed a greater and greater flow of heat came from the deep central regions and less and less of the heat lost to the environment originated in the muscular tissues. Throughout the period of stable hypothermia the temperature gradient between the core (rectum) and the muscular tissue of the thigh was significantly greater than during the control period, suggesting that the flow of heat depended primarily on conduction. The values for the ‘thermal circulation index’ of the hind footpad, thigh and foreleg were found to decrease as a result of hypothermia while the index for the ear and chest showed no significant change. These results, together with the evidence on the temperature gradients indicate that the induced hypothermia resulted in an increased volume of the ‘shell’ and a consequently reduced volume of the ‘core’. Since there was no appreciable change in the index for the chest, a relatively greater proportion of the heat lost to the environment must have occurred from the surface of the trunk.

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