Theoretical evaluation of contributions of heat conduction and countercurrent heat exchange in selective brain cooling in humans.

The purpose of this work is to evaluate the capacity of the heat loss from the carotid artery in the human neck and thus, to provide indirect evidence of the existence of selective brain cooling in humans during hyperthermia. A theoretical model is developed to describe the effects of blood flow rate and vascular geometry on the thermal equilibration in the carotid artery based on the blood flow and the anatomical vascular geometry in the human neck. The potential for cooling of blood in the carotid artery on its way to the brain by heat exchange with the jugular vein and by radial heat conduction loss to the cool neck surface is evaluated. It is shown that the cooling of the arterial blood can be as much as 1.1 degrees C lower than the body core temperature, which is in agreement with previous experimental measurements of the difference between the tympanic and body core temperatures. The model also evaluates the relative contributions of countercurrent heat exchange and radial heat conduction to selective brain cooling. It is found that these mechanisms are comparable with each other. Results of the present study will help provide a better understanding of the thermoregulation during hyperthermia.