Listen: Hypothermia

MPR’s Jo Ann Shroyer reports on University of Minnesota-Duluth hypothermia study in the freezing waters of Lake Superior.


1985 MMA Award for Excellence in Medical Journalism, Radio category


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JO ANN SHROYER: Out here in Lake Superior, the water is a cool 39 degrees. It doesn't ever get much warmer. Year round, it's between 40 and 45 degrees Fahrenheit. If you fell in wearing regular clothes, after 20 minutes, your body temperature would begin to fall dangerously.

At 95 degrees, you'd be hypothermic. Your heart would slow down. Your brain wouldn't get enough blood. If help didn't come, you would die.


Researchers at the University of Minnesota in Duluth have been studying hypothermia for six years with the help of willing students who would immerse themselves in tanks of cool water. But Drs. Robert Pozos and Larry Wittmers have worried that there were conditions out in the lake that couldn't be duplicated in a laboratory tank. That's why we're on this Coast Guard boat, cruising out into Lake Superior on this gray and windy November day.

For $100, graduate student Scott [? Eskridge ?] will jump into the lake wearing a special fluorescent suit that both insulates and floats. It is meant to be easily spotted by rescuers.

SPEAKER 2: You all right, Scott?

SPEAKER 3: Yeah.

[? SCOTT ESKRIDGE: ?] It's cold. It's cold.

JO ANN SHROYER: Scott is tethered to the boat by a rope and wires connected to rectal and chest thermometers. First, there's the shock and the pain of cold water, which flows into the suit where it will eventually be warmed by Scott's body heat and serve as another insulating layer. Scott bobs stiffly up and down on the surface next to the boat. And after a few seconds, begins to shiver violently.

His body has done several things already to protect itself. He stiffens. Unnecessary movement wastes heat. Then he begins to shiver violently, producing heat in his muscles and attempt to keep his surface from cooling off.

Blood circulation withdraws from his extremities immediately and concentrates in the core of his body, protecting his heart, lungs, and brain, which must keep functioning, if Scott is going to stay alive. If Scott had been drinking alcohol, none of these things would have happened. Alcohol dilates the blood vessels.

Blood would have stayed in his limbs. He wouldn't have shivered. He would become hypothermic much quicker. After 20 minutes in the water, Scott's core temperature measured by the rectal thermometer has actually risen by 3/10 of a degree.

This won't last. But so far, his body's defense mechanisms are working well. His skin temperature has dropped 13 degrees.

[? SCOTT ESKRIDGE: ?] I can warm up, I guess. I'm getting warmer. I don't know what my temperatures are, but I can feel like my legs are back to feeling good again.

JO ANN SHROYER: Scott begins to paddle with his feet and fool around in the water. Pozos says it's time for a dive reflex test. Water on the face or hands will often trigger this.

ROBERT POZOS: Flip over. We want you to flip over.

SCOTT ESKRIDGE: And stay over?

ROBERT POZOS: Flip over and then stay over. Count to 10 and flip back.

SPEAKER 2: OK, any time?

ROBERT POZOS: It's up to you.


[? SCOTT ESKRIDGE: ?] We have no choice. Just wait.

ROBERT POZOS: OK, flip over.

JO ANN SHROYER: Scott's face grimaces with pain. His heartbeat quickens. The dive response is supposed to slow the heart rate. It can be dangerous to adults, slowing the heart till it damages itself.

Pozos says the dive reflex works best in children. After 30 minutes, Scott's body has done all it can do to keep him warm. He begins to lose ground. Pozos pulls him out of the water because his body temperature has started to fall 1 degree every minute. In another hour, he would be hypothermic.

ROBERT POZOS: How are you doing? How's the legs?

[? SCOTT ESKRIDGE: ?] They're not all right.




[? SCOTT ESKRIDGE: ?] Those feet are frozen.

ROBERT POZOS: Feet are frozen. The reason I pulled him, his temperature, like I said, it was falling pretty fast. He's fine, though. He's not anywhere near being hypothermic yet.

JO ANN SHROYER: Scott is hustled into the engine room, where he's dressed in dry clothes and warms up. He's hungry. Tomorrow, he'll be sore and tired but alive. Robert Pozos says, people can stay alive in cold water if they don't panic.

ROBERT POZOS: I really tell people, they fall in cold water, if you survive the first 15 minutes, you can go a long time, if you play it cool and you have some kind of survival gear. The first 15 minutes is really what's the most difficult.

SPEAKER 3: Johnny, come back down.

JO ANN SHROYER: It's important not to thrash about in the water. It wastes heat. Dress right, use special gear meant for survival in cold water. And above all, use some kind of flotation, at the very least, a life jacket or vest. The experiment on the lake was a success.

Pozos says, the effects of the cold water were faster than in the laboratory tanks. Something happens in the wild water of a real lake that can't be duplicated in a lab. Pozos and Wittmers will be studying their data all winter.

The Coast Guard boat cruises back towards the hills of Duluth where the lights are blinking on. A light snow is falling. Soon, the lake will ice up. People won't be venturing out onto the lake until spring, when the Coast Guard says there will be plenty of accidents. And knowledge about hypothermia could save lives. I'm Jo Ann Shroyer.



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