Selective Brain Cooling
Besides the general “heat intolerance”, ETS patients have anecdotally reported what they consider to be a “hot brain” syndrome. In particular, Taiwanese ETS patient and robotics engineer “Hpymaker” has made frequent references in the oral history to this hot brain phenomenon. Songboy1234 has also reported a very disturbing sensation like a fever that occurs when exercise is attempted.
Is there any scientific reason to suppose that ETS surgery could interfere with brain cooling, separate from the general thermoregulatory difficulties already shown? This would depend upon whether the normal human has any mechanism to selectively cool the brain; and if so, whether that mechanism is damaged by sympathectomy. The answers are yes we do; and yes it is.
Studies from decades ago began to confirm Selective Brain Cooling. “Cooling of the head skin . . .produces a significant improvement in the performance of heat-stressed humans.” (Kenney, see Williams & Shitzer, 1974).
The ability to selectively cool the brain during hyperthermia (overheating) has long been an accepted fact in many mammals, such as dogs. Dogs have a network of blood vessels in the head called the “carotid rete” which allows heat exchange between warm blood in arteries and cooler blood in veins. The excess heat escapes through the mouth during panting. Humans do not have a carotid rete, so for some time the notion of selective brain cooling in humans was controversial.
However, it has been shown that at 65.8˚ F (18.8˚ C) ambient temperature the deep trunk temperature of a marathon runner may rise to 107.4˚ F (41.9˚ C) with no clinical sign of heat illness (Cabanac et al. 1979; see Maron, Wagner & Horvath, 1977). Michel Cabanac at the Department of Physiology, Laval University, Quebec has been studying Selective Brain Cooling in Humans since the 1970’s, and has evidently discovered the mechanism by which humans accomplish this.
It turns out that certain veins in the face, such as the ophthalmic veins, will actually reverse the direction of blood flow when the body begins to overheat. The blood in these veins is cooled by evaporation of facial sweat, then flows backwards into the sinus and intercranuim area, cooling the carotid artery and the brain.
“The selective influence of facial fanning on human brain temperature can be attributed, therefore, to cool venous blood perfusing the cavernous sinus and possibly cooling the blood of the internal carotid artery.” (Cabanac et al. 1979)
A group of Japanese physiologists at Kanazawa University have been confirming and expanding upon Cabanac’s findings. Their studies subject people to heat stress and exercise, and measure variables such as skin temperature, core temperature, forehead sweating, and blood flow in the ophthalmic vein. They found “that there are elements within the brain that control the mechanisms for switching the direction of venous flow through the emissary veins to keep the brain cool during hyperthermia.” (Hirashita et al. 1992)
Given that this direction-reversing mechanism requires vascular control in the face, we already have strong reason to suspect that ETS would disturb if not destroy selective brain cooling. Is head sweating also important to this process?
“The efficiency of SBC (Selective Brain Cooling) is increased by evaporation of sweat on the head and by ventilation through the nose.” (Nagasaka et al. 1998)http://www.editthis.info/corposcindosis/Changes_to_Systemic_Function%2C_part_1
