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University of Minnesota
University of Minnesota

Extreme heat is not so hot

July 31, 2012

A dripping ice cream cone on a table near Lake Harriet.

The last time the high temperature was below 80 degrees in the Twin Cities was June 25.

Photo: Rick Moore

U cardiologist explains how heat takes a toll on our bodies

By Rick Moore

Now is the summer of our discontent. Or at the very least, of our extreme discomfort.

The summer of 2012 is burning a mark in the record books. So far there have been 24 days with highs of 90 degrees or above in the Twin Cities (the average is 13) and two days with highs topping 100.

We are currently in the midst of a 35-day streak in which it has been 80 or above. Given that the average high is only supposed to be 83 or 84 in the depths of summer, that’s quite a streak.

This certainly isn’t as extreme as the Dust Bowl year of 1936, during which the Twin Cities saw highs of 100-plus degrees eight times in a nine-day span, but the prolonged heat (coupled with near tropical dew points), should keep everyone on guard about maintaining their health.

On average, approximately 1,500 Americans die from heat each year, according to meteorologist Paul Douglas, and that’s more than die in tornadoes, floods, hurricanes, and blizzards combined.

Staying healthy in the heat

Prolonged heat waves and/or intense heat naturally take a toll on our bodies, according to Daniel Duprez, a University cardiologist and professor of medicine.

When overheated, the body tries to cool itself off and blood vessels start to dilate, Duprez says. Vascular resistance goes down, and so does blood pressure. The body then naturally regulates the blood pressure and tries to compensate by increasing the cardiac output, mainly due to an increase in heart rate. The increase in heart rate requires more oxygen for the heart. And therein lies the strain, especially for those with compromised cardiovascular systems, coronary heart disease, or chronic heart failure.

The steamy days also put people at elevated risk to develop heat stroke. “If you do not take enough fluids—especially for people who work outside or who participate in sports outside—you get dehydrated,” Duprez says, “and then that can have a major impact on your kidneys.” 

Even for those who have no desire to overexert during a heat wave, there’s a huge barrier to resting up, especially if it stays balmy overnight and you lack air conditioning.

“A lot of people develop sleep problems. They sleep less and they don’t sleep well,” says Duprez. “This disrupted sleep will have an impact on general well-being. … People will be more tired and they will become a little bit more irritated, too.”

It’s wise for everyone to watch their activity in the heat, and of course stay hydrated, but that especially applies for people at risk.

“I think the general rule is if people already have underlying heart or lung conditions, they need to avoid strenuous exercise [outdoors] between 10:00 in the morning and 5:00 or 6:00 in the evening,” he says. “You tell that to people so much [but] a lot of people will still think that they’re immortal."

Tags: Academic Health Center