Re: Brain size and sweat

D. Eric Greenhow, M.D.,Ph.D. (
Thu, 09 Jan 1997 14:12:04 -0500

This is my first significant posting, so I should introduce myself. I grew
up in the Plymouth Brethren, became a Presbyterian in 1967, and am a member
of the PC(USA), (the denomination considered apostate by many evangelicals.)
I graduated from the Univ of Toronto in 1956 with an M.D., was a "country
doctor" (House calls, delivering babies, setting fractures etc,) I joined
the faculty of the Department of Anesthesia in 1971, and received a Ph. D.
from the University of Pennsylvania's Graduate School of Education in 1991.
My area of expertise in Education is the definition and measurement of
competence in physicians in training, especially in the specialty of
Anesthesia. My expertise in anesthesia is in Thoracic, Vascular and Kidney
transplant surgery.

I qualify for this discussion because I have practical experience in heat
regulation and heat transfer in the human body.

Back in paleoanesthetic times, (1970s and early 80's) it was thought that
the brain could be protected in a practical way during carotid
endarterectomy (a procedure for removing an atheromatous plaque from the
lining of the carotid artery) by surface cooling. This is a difficult job,
since the body resists the lowering of temperature. (Under general
anesthesia thermal regulation is also anesthetized, and most patients become
stabilized if unprotected at about 35 C. Only a few become poikilothermic,
with relentless drops in temperature.) General anesthetic was required
because of the discomfort, and paralysis to prevent shivering. Even so, it
took almost 2 hours to cool the body to the 31 or 32 degrees C thought
necessary, the surgical procedure took an hour or a little less, and
rewarming took at least an hour before the anesthetic could be reversed.
During cardiopulmonary bypass it is a trivial chore to reduce the
temperature to any temperature (the lowest I ever did was to about 13 C).
There is tremendous heat loss under anesthesia from any procedure, through
the scalp, not because of brain blood flow, but because of scalp blood flow.
(The victims of scalping died not from the trauma necessarily, but because
of massive hemorrhage from the scalp.) Most well trained anesthesiologists
protect against loss of heat from the scalp through the use of a skull cap
made of lined aluminum foil.

There is a rare but dreaded familial disease, Malignant Hyperpyrexia, in
which certain anesthetics cause the victims to develop muscle contractions
similar to those of post-mortem rigidity, with rapid production of CO2,
lactic acidosis, and heat, with temperatures rising within 4 to 5 minutes to
45 C or so. Untreated this is always fatal.

For the reasons given above, anesthesiologist know a great deal about heat
and its production, loss etc. I would suggest that those who wish further
reading about heat production, loss etc consult a CURRENT anesthesia text
(Miller &c, Barash &c, Longnecker &c, or others). Beverly Britt in Toronto
has done more in the field of malignant hyperpyrexia than anyone else.
Henry Rosenberg in Phiuladelphia developed a test for the condition in which
a muscle fiber from the suspected person is stimulated in a bath of caffiene
of a certain concentration. The normal person's muscle responds normally,
the abnormal has a tetanic contraction.

Incidentally, the minipigs, especially a breed from Australia, are also
subject to Malignant Hyperpyrexia, and have been used in the study of this

I have always thought that the reason pigs wallow is because their sweating
apparatus is so inefficient that they can lose heat through the moisture of
mud, and so love to wallow.

Dogs lose heat through very rapid ventilation, done in such a manner that
they do not ventilate excessive CO2, since that must remain at about 40 mmHg
in the blood, but only ventilate water vapor containing heat through this
manner of respiration.

I trust this brief overview from someone with practical experience in the
area is of help to the discussion.