Northwesterners not acclimated for record heat

You might find it hard to believe at the moment, but your body was built for heat.

Experts say humans are remarkably adept at coping with high temperatures — but that doesn't lessen the misery for Northwesterners who saw temperature records topple Wednesday as SeaTac airport reached 103 degrees.

"We are basically warm-weather animals," said Michael Sawka, chief of the Thermal and Mountain Medicine Division at the U.S. Army Research Institute of Environmental Medicine in Massachusetts.

Sweating, dizziness and a racing pulse are all signs that the body is trying to keep itself cool, Sawka said. With prolonged exposure to high temperatures, the body becomes more efficient at it. But when folks accustomed to Western Washington's mild weather are suddenly thrust into the oven, their bodies sputter like poorly tuned engines.

"It can really knock you silly," said University of Washington biologist Ray Huey, who has studied lizards and other denizens of the Kalahari Desert.

From Everett to Olympia, people are feeling the physical fallout, which begins with more blood being routed to the skin for cooling. "We are really blessed with this large surface area to exchange heat," Sawka said.

But pumping more blood to the skin makes the heart work harder and decreases the blood supply to the gut and other organs. The result is a feeling of malaise.

Sweat glands kick on, bathing the skin in perspiration that provides a cooling effect — if the air isn't too humid to prevent evaporation.

When the body becomes dehydrated or too hot, some tissues can leak toxins into the blood stream and muscle damage can occur.

"When you haven't acclimated, you get this general discomfort," Sawka said. "Your skin is wet and hot, your cardiovascular system is strained and maybe you didn't drink as much water as you should, so you're dehydrated, too."

Folks who are acclimated to heat start sweating sooner and perspire more. The sweat is more diluted, so the body doesn't lose precious salt. The process is better paced, so the sweat evaporates quickly. "People in places like Phoenix will say: 'I hardly sweat at all,' " Sawka said. "They're actually sweating a lot, but they don't notice because their skin stays dry."

Compared with a Seattleite, an acclimatized person in Houston and other steamy climes also has a heart that pumps more effectively and doesn't beat as fast when the mercury soars.

Heat effects unfold on a microscopic scale, too. Cells crank up production of "heat shock proteins" when temperatures rise. These molecules help repair enzymes and other cellular machinery that can be damaged by heat, said Dr. Larry Sonna, a critical-care physician at the University of Maryland Medical Center.

There's some evidence that heat-adapted individuals may produce more of these healing proteins.

"Your heat-acclimation response is wonderfully protective," Sonna said.

Huey, the UW biologist, experienced the benefits first hand chasing lizards in Texas' Big Bend National Park in July. "It was stinking hot," he said. "The first day or two I really suffered, but eventually it wasn't nearly as debilitating."

Almost everyone — including the most shade-loving Northwesterner — has some ability to acclimate to heat. But a few people claim they never get used to it, and they could have a point.

It's likely that folks who spend their early years in a warm climate are somehow primed to better shrug off the heat, Sawka said. One Army analysis found that recruits from northern states are more likely to get sick from the heat than those from the South. Another study found that people born in hot places had more sweat glands than people born in cool places.

Some people, especially the elderly, find it harder to shed heat because of heart problems, sickness, or the side effects of medication. Recent research suggests people suffering from infections might be more susceptible to heat. Others are handicapped by girth. "Those of us who are pleasantly plump have a layer of insulation that interferes with eliminating heat," Sonna said.

Although people adapt to heat better than to cold, high temperatures can kill. A 2008 study found heat waves are the leading cause of death from natural disasters in the United States.

Some area hospitals and clinics reported numerous patients over the past several days suffering from dizziness, rashes and dehydration.

Temperatures in the high 90s to 100 are forecast for Western Washington today. On Friday through the weekend, highs are expected to cool into the upper 80s.

The heat wave has been long enough to give locals a leg up on acclimation, which can start to take hold in as little as five days, Sawka said. The process is usually complete within 2-3 weeks. But don't expect your tolerance to rise if you never go outside, he added.

"If you're sitting in an air-conditioned office, you don't acclimatize."

The military has perfected an approach that speeds heat acclimation, but no one should try it at home, Sonna said: When soldiers spend 90 minutes a day sweating profusely on a treadmill in a saunalike room, they adapt to the sweltering condition in as little as 10 days.

Sandi Doughton: 206-464-2491 or sdoughton@seattletimes.com