Concept of Selective Brain Cooling and Its Implication

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Selective brain cooling (SBC) can occur in hyperthermic humans despite the fact that humans have no carotid rete, a vascular structure that is located at the base of the skull and which facilitates countercurrent heat exchange between carotid arteries and jugular veins in some mammals. In humans, an increase in flow of the emissary and angular-ocular veins contributes to SBC. The efficiency of SBC is increased by evaporation of sweat on the head, particularly by means of forced fanning, and of water from the nasal mucosa by means of hyperventilation. The efficiency of the SBC is also increased by changing the body posture from supine to upright position, which increases emissary and angular-ocular venous flows by means of an increase in the gradient of intravenous pressure between the vasodilated head skin and the intracranial space. A forced increase in respiratory evaporative heat loss from the upper respiratory tract facilitates SBC, as observed in horses, which have also no carotid rete. Knowledge of human SBC, facilitating heat loss from the head, avoiding headgear, increasing ventilation by dilating the athlete’s nostrils, etc., is likely to improve the health and comfort of subjects exposed to extreme hot environments for their work, during sport events, or for therapeutic reasons. The validity of using tympanic temperature as an index of brain temperature is also postulated.