ALTITUDE SICKNESS, PART 1
You’ll probably never need the direct attentions of the Himalaya Rescue Association. But if you like to ski or hike or just take in the view from 8,000 feet, you may need their advice on how to recognize and respond to what often is called mountain sickness.
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Not everyone agrees on what altitude itself is. The Himalaya Rescue Association, now based in Nepal, says “high altitude” is between 5,000 and 11,500 feet. The National Outdoor Leadership School, based in Lander, Wyo., says “high altitude” is between 8,000 and 14,000 feet. There is another category, “very high altitude,” which the two groups define differently. But when it comes to “extreme altitude,” both agree that that means anything higher than 18,000 feet.
When it comes to altitude sickness, how high is not as important as how soon. On that point, these two groups agree. Everyone’s body has its own limitations, but most people don’t experience problems below 8,000 feet. Above that level, though, the rate of ascent becomes critical. That’s because the body must make several adjustments, called acclimatization, to the changing environment. Respiration deepens, blood pressure in the pulmonary arteries increases and more red blood cells are produced, says Rick Curtis, director of Princeton University’s Outdoor Action program. Other changes include an increased heart rate, a shift of blood flow to the brain and the development of more capillaries, according to the National Outdoor Leadership School.
Those changes take time. One rule of thumb recommends that above 8,000 feet (some say 10,000 feet), do not ascend more than 1,000 feet per day; and for every 3,000 feet gained, take a day to rest.
Next week: Symptoms and treatment.