By Alissa Levy,
CBC News Online
"Everything about being at altitude is hard...
that's what makes Everest Everest."
- David Breashears, high altitude alpinist
Climbers say Everest isn't technically a hard climb, but it's so high and the air is so thin. The height, from Basecamp at 5,350 m to the summit at 8,850 m, is the biggest physical challenge facing those who attempt the climb. The painfully thin air slows fit mountaineers to a crawl, impairs their judgment, dulls their thirst and appetite and, over time, can pose a threat to their lives.
"Many times, I have seen people with vision problems (including blindness), the loss of speech (known as aphasia), dizziness, confusion, and partial paralysis.
In each case, the best thing to do is get on the oxygen and get down fast!"
- Eric Simonson, Mountain Zone dispatch
There is a normal amount of oxygen in the air at the summit of Everest. But you can't get it into your lungs because of the change in atmospheric pressure. At sea level a barometer reads 760 mm, at the top of Everest it reads 249. Under these circumstances it feels as if only part of your lungs is working so it's very hard work to catch your breath. It's like you are hyperventilating because you are breathing three times as fast to get the same amount of oxygen.
Some climbers are able to cope with this, although with extreme difficulty. Some of them even make it to the summit and back without bottled oxygen, but that is rare. Most climbers, including Byron, use oxygen tanks and masks when they get above Camp 4 at 8,000 m. It helps get more of the vital gas to their lungs.
Without oxygen climbers can experience hypoxia, or lack of oxygen to the brain. This makes them disoriented, confused and can bring about hallucinations. Imagine trying to make life and death decisions under these conditions. Breathing bottled oxygen can help stave off hypoxia but it won't make a climber feel like they're back at sea level and it can have discomforts of its own.
"A lot of people have the experience of their throats getting incredibly dry, saliva in their mouth basically turns to rubber cement, of the same sort of consistency, and heaven forbid that their nose should even dream of running because there is very little you can do about the accumulation of mucus/snot in your oxygen mask.
It's just going to carry on building up there during the day, and you'll have to live with it."
- Charles Corfield, Mountain Zone dispatch
Even with oxygen, acute mountain sickness (AMS) can take its toll on a body. Climbers may have to endure everything from headache, dizziness, and trouble sleeping to nausea, vomiting and lack of coordination. Altitude can bring on two other particularly dangerous ailments: HAPE (high altitude pulmonary edema) and HACE (high altitude cerebral edema). "With pulmonary edema the blood vessels in the lungs start to leak this plasma fluid that is tinged with red blood cells so it's a little pinkish and the air sacs start to fill up in different parts of the lung ... and eventually they fill up with fluid and a person starts coughing this pink frothy spew. They can't get any air at all."
- Peter Hackett, MD, high altitude physiologist
HACE, or high altitude cerebral edema is an accumulation of fluid on the brain. The symptoms include staggering, confusion, and hallucinations. The only cure is to move to lower altitudes right away.
If you can't get down fast enough it may help to go on bottled oxygen or spend some time in a Gamow bag, a portable pressurization chamber that artificially increases the atmospheric pressure, simulating a lower altitude. In extreme cases you could also inject dexamethasone. Dex is a steroid that can temporarily negate the effects of altitude, giving a climber time to make it down the mountain. Climbers often carry a vial of dex under their down suits as a precaution. One of the odd things about altitude sickness is that it's unpredictable. One year a climber can have few problems, the next year they can be struck with HAPE or HACE. Even Sherpas, whose bodies are well adapted to these heights after generations of living at altitude, can be struck with these illnesses. But all climbers take precautions to lessen the perils.
They spend time at various levels to let their bodies adjust to the thinner air. They will stay at Basecamp, where there is half the amount of oxygen available at sea level, for several days before heading up to Camp I for an overnight stay. They may take a climb up to Camp II but instead of staying overnight, they'd come back to Camp I and then all the way down to Basecamp, giving their bodies time to rest and acclimatize.
 Fluids can help climbers acclimatize.
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Next, they'd head right to Camp II for an overnight stay, climbing up to Camp III for a day, and so on until their bodies are fully acclimatized. The body actually undergoes physiological changes as it's taken to higher altitudes. Taking time to rest at each level lets the circulatory system produce more red blood cells to carry oxygen to all the muscles and tissues.
"Although there are rules, and most intelligent climbers follow them, it seems ultimately it is Chomolungma, the Tibetan word for Everest, goddess mother, who decides. Those who initially seem strong suddenly get weak, those who remain strong can be turned back by bad weather."
Virginia Robinson, AGF Everest 2000 Physician's log
Climbers only acclimatize as high as Camp III (7,200 m). They won't go to Camp 4 until the summit push. At that altitude, above 8,000 m, the body can no longer acclimatize and it simply begins to break down. Humans can not survive more than a few days at this height, commonly known as "The Death Zone."
 Questions Kids Ask
What is thin air?
Answer: At sea level the atmospheric pressure is 760 mm of mercury. At the top of Everest, the highest point on earth it is only 249 mm of mercury. What this means is that there is only one third the amount of oxygen to breathe on top. More ...
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