Engines of Our Ingenuity

No. 362:

by John H. Lienhard

Click here for audio of Episode 362.

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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