What Happens When The Body Overheats?

As the heat wave continues, Michele Norris talks to Larry Kenney, professor of physiology and kinesiology at Penn State University, about what happens to the human body when it overheats.

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MICHELE NORRIS, host:

Given the extreme heat, folks are being told to stay inside if they can, drink lots of water, avoid physical stress. We wanted to get a sense of just how extreme heat affects humans and who's most vulnerable. So we're joined by Larry Kenney. He's a professor of physiology and kinesiology at Penn State University.

Mr. Kenney, welcome to the program.

Professor LARRY KENNEY (Physiology and Kinesiology, Penn State University): Thank you very much. Glad to be here.

NORRIS: What are the most common heat-related symptoms?

Prof. KENNEY: The most common heat-related symptoms are those associated with both heat exhaustion and heatstroke, and the early symptoms involve such things as goose bumps, tingling sensation in the skin, kind of a dull headache, nausea. Those things really portend one of those two diseases, either heat exhaustion, which is really a disease of dehydration that causes cardiovascular strain, or the more serious heat illness, heatstroke.

NORRIS: Now, is one of the danger signs in that case when people stop sweating, if you're not sweating and you're in extreme heat, should you be concerned?

Prof. KENNEY: Well, eventually in heatstroke, sweating stops in - somewhere around 50 percent of all cases. So we used to teach people in health class that the only people who are suffering heatstroke were those who stopped sweating. That's not true, and it's also dangerous because you may have stopped sweating half an hour ago but if it's still hot, and especially if it's still humid, the sweat that you produce stays on the skin, and there's no way of knowing that you've stopped sweating.

NORRIS: When a body starts to overheat, what happens? What's the danger?

Prof. KENNEY: Heatstroke is a very insipid disease. The two classical ways to diagnose heatstroke are an elevated body temperature, that is in the range of 104 to 106 degrees Fahrenheit, and some sort of cognitive mental impairment.

That could be agitation, it could be confusion, it could be lethargy. And that's because when human body temperature gets above 104 degrees, the most vulnerable tissues to heat strain in the body are nerve cells. And because the brain is comprised almost entirely of nerve cells, those are the most sensitive and vulnerable tissues.

NORRIS: What happens internally when you're exposed to extreme heat over an extended period of time?

Prof. KENNEY: So when our body temperature starts to increase, the blood flow to the skin increases, and that puts a strain on the heart, and we are capable of producing large volumes of sweat, which causes dehydration, which puts further strain on the heart.

NORRIS: So it sounds like drinking lots of liquid is important, a lot of water, perhaps a little bit of iced tea?

Prof. KENNEY: You know, it really doesn't matter in most cases what type of fluid people consume. It should be cold because that makes it more palatable and has a slight cooling effect on the body.

We used to tell people to avoid caffeine because there was a notion out there that it's a diuretic, and it is, but it also provides lots and lots of fluid in excess of its diuretic effect.

NORRIS: Larry Kenney, thanks so much.

Prof. KENNEY: You're very welcome.

NORRIS: That's Larry Kenney, he's a professor at Penn State University.

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