Today, let's cool your blood. The University of
Houston's College of Engineering presents this
series about the machines that make our
civilization run, and the people whose ingenuity
created them.
A Shakespearean lady
describes the death of Falstaff in Henry
V. She says:
[He] bade me lay more clothes on his feet ...
They were cold as any stone. ... I felt to his
knees ... and all was cold as any stone.
The idea that cold signals coming death
is very old. Hippocrates said that cold ears meant
death was near.
Aristotle thought that hibernating animals endured
a winter-long death when they lowered their body
temperature. He believed they were reborn in the
spring. The Greeks believed that disease resulted
when the natural balance between opposites broke
down. So the body was in trouble if either cold or
heat dominated.
The Greeks spun these arguments without any clear
understanding of heat and cold. It was a plain
enough fact that fever and chill signaled illness.
Not just the effects of temperature change are
clear. We also use a dramatic array of means for
keeping our temperature at 98.6 degrees. We sweat
because evaporating water soaks up heat when we
have to get rid of it. We shiver to generate warmth
by mechanical action. Gooseflesh is our attempt to
make our hair stand on end. That makes hair into a
better insulator.
Still, cold also has power to buy time for a
surgeon. Napoleon's surgeons on the retreat from
Moscow found that when they amputated chilled
limbs, patients suffered and bled less.
Surgeons do this today with a technique called
Hypothermic Circulatory Arrest. That means taking
blood from the patient's body and running it
through a cooler. When they return the cooled
blood, the patient goes into a brief hibernation.
Chemical processes slow down. Breathing can be
stopped long enough to finish an operation. So can
blood circulation, in all or just part of the body.
Surgeons can extend the length of any operation
that requires cutting air or blood circulation, if
the body's cool enough.
This is a dangerous business. Hypothermia may be
the analgesic that makes the end bearable for a
sailor fallen overboard in Arctic waters. But it's
also what kills him. The rate and length of cooling
must be held to delicate limits. Uneven
temperatures in the brain will damage it. All this
means inventing elaborate protocols. The pace of
cooling, and of the operation itself, has to move
with the precision of a ballet.
Maybe this really does amount to inducing temporary
death in the patient. That, after all, is a matter
of definition. But it is a death that sustains
life.
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds
work.
(Theme music)
Shitzer, A. and Eberhart, R.C., Introduction.
Heat Transfer in Medicine and Biology: Analysis
and Applications. Vol 1, (A. Shitzer and R.C.
Eberhart, eds.). New York: Plenum Press, 1985.
Olsen, R.W., Hayes, L.J., Wissler, E.H., Nikaidoh,
H., and Eberhart, R.C., Influence of Hypothermia
and Circulatory Arrest on Cerebral Temperature
Distributions. Journal of Biomechanical
Engineering, Vol. 107, No. 4, 1985, pp.
354-360.
The Engines of Our Ingenuity is
Copyright © 1988-1997 by John H.
Lienhard.
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