At 19,000 feet, Peter Hackett started to feel awful.
While hiking a peak in Bolivia, Hackett developed a bad headache, felt nauseated and drowsy and started to lose his coordination.
"It came on so quickly and was so severe, I had to immediately descend," said Hackett, a physician and expert in altitude sickness at the University of Washington in Seattle.
Hackett's troubles are common for flatlanders who ascend to high altitudes too fast. But recent research shows not everyone is as vulnerable. And, it turns out, different groups of people have evolved different ways of adjusting to living in high altitude, low oxygen places.
Scientists are just starting to understand these differences and they say their work could someday help flatlanders like Hackett trek in good health.
Understanding how thin air affects the lungs and brain could also extend beyond the relatively small world of climbers and skiers who suffer from altitude sickness. It could also lead to new treatments for other afflictions, including migraines and obesity.
"I think we've only begun to scratch the surface when it comes to finding common ground with other conditions," said Robert Roach, research director at the Colorado Center for Altitude Medicine and Physiology in Denver.
Heavy Breathers, Thick Blood
Even top athletes are vulnerable to the symptoms of acute mountain sickness, which range from headaches to dizziness to severe nausea and vomiting. Above 14,000 feet, two afflictions can become deadly - high altitude pulmonary edema (HAPE), which results from the constriction of blood vessels and build of fluid in the lungs, and high altitude cerebral edema (HACE), a swelling and build up of fluid in the brain.
One way to understand how high altitude makes some people sick is by understanding why others don't get sick.
Cynthia Beall of Case Western Reserve University in Cleveland, recently examined inhabitants of plateaus in Tibet, Ethiopia and the Andes and found that each group of people have developed their own ways of boosting their bodies' oxygen levels.
Indigenous people of the Andes, she found, carry more hemoglobin - a carrier of oxygen - in their blood.
"There are fewer oxygen molecules in a breath and so with more hemoglobin you have a bigger sponge, essentially," explains Beall.
Tibetans, who have the longest history of living in highlands, have evolved a completely different, and some argue, superior strategy - they breathe more. By increasing their rate of breathing, Tibetan highlanders cram more oxygen into their lungs.
Meanwhile, Ethiopians living in the highlands of East Africa have adapted in ways that scientists don't yet understand. Their blood appears to have normal levels of hemoglobin, says Beall and their breathing rate is not unusually rapid. Still they somehow extract more oxygen from the thin air.
"It's as if they weren't even at high altitudes," she said.
The findings are of interest to anthropologists who use the adaptations as markers to measure how long people have lived - and evolved - in the high altitude regions.
The information is also useful to those looking for ways of helping people avoid altitude sickness.
Diamox, a drug commonly prescribed for HAPE, borrows a trick from native Tibetans and stimulates faster, deeper breathing.
Hackett explains that most people going to high altitudes begin to gradually build up more hemoglobin in their blood to carry more oxygen - as the Andean people naturally do. But having too much hemoglobin can become a problem for most.
"It's like having motor oil in your blood," he said. "It gets too thick and you get sick and have trouble sleeping."
Understanding how native high-altitude Andeans increase their hemoglobin levels and manage to avoid the "motor oil" problem could be instructive. Hackett and Beall are also interested in the body's ability to produce nitric oxide - an agent that effectively expands the diameter of blood vessels and prevents constriction of blood vessels the lungs.
Some people automatically produce more nitric acid when exposed to thin air, but not everyone is so naturally equipped. In recent years, scientists have found that Viagra, a drug designed for an entirely different purpose, has similar effects as nitric oxide and triggers the expansion of blood vessels in the lung (as well as in a lower organ), preventing pulmonary edema.
"There aren't many people who get pulmonary edema in high altitudes," said Hackett. "So it won't be a huge use of the drug, but it seems to be effective."
At the Colorado Center for Altitude Medicine and Physiology, Robert Roach is looking for news ways of preventing and treating altitude sickness in research that he hopes will extend benefits to those in all altitudes.
New Cures for Migraines, Obesity?
Altitude headaches and migraines, for example, may share some features. Roach hopes by investigating altitude headaches he may stumble upon new explanations and possibly treatments for migraines, which afflict about 24 million Americans.
Roach has two main tools at his disposal: a chamber that mimics the low oxygen atmosphere of high altitudes and a magnetic resonance imaging machine that takes snapshots of the brain.
"It's more difficult to study migraine sufferers because their headaches aren't very predictable," Roach explained. "But altitude is very reproduceable. If I put you in our high altitude chamber, I can give you a real bad headache."
Another realm of interest is obesity. For reasons that scientists don't yet fully understand, people who spend time in high altitudes tend to shed weight.
Roach cautions, "We're still shooting in the dark," but he and his colleagues are investigating whether subjecting people to the effects of high altitude by having them sleep in specialized tents at night, might lead to weight loss.
"It may not be rocket science," he said. "But we may learn something we don't know about obesity and weight loss."
Although people like Roach, Beall and Hackett are learning more about the afflictions associated with high altitude, they all emphasize that simple awareness is the best way to avoid trouble.
Roach points out that altitude sickness is mostly a modern one since airplanes can now transport people to high altitude places like Telluride, Co. (at 9,000 feet) fairly quickly. Forcing the body into this kind of abrupt adjustment is what leads to problems.
"In the old days it usually took months to get to high altitudes so the body had time to adjust," he said. "That window of adjustment is critical. Today, people fly to Colorado to go skiing and have no clue they could be vulnerable."
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