It’s called the Death Zone: the region on Mt. Everest above 25,000 feet where the risk of dying is highest. Those risks include hypothermia and frostbite, but the greatest risk of all would exist even if the top of the mountain were as balmy as the Bahamas: high-altitude sickness.
Human beings evolved as sea level, or close to it, where the blanket of air pressing down on us is thickest, and the air pressure is therefore greatest. As you ascend, that blanket of air grows thinner above you, and so air pressure decreases. It’s not that there’s less oxygen in the air at high altitudes–percentage-wise, there’s the same amount; it’s just that the air molecules are spread out more, so that each breath pulls in much less air, and therefore much less oxygen, then it does at lower altitudes.
On Mt. Everest’s 29,028-foot peak the air pressure is only one third what it is at sea level–so low that, as experiments in decompression chambers in the early part of this century proved, a human being plucked from sea level and unceremoniously plopped on the top of the mountain would lose consciousness within minutes and die soon after. Fortunately, it takes a long time to get to the top of Everest, and if the ascent is made carefully and slowly enough, the body can acclimate–somewhat.
The problems actually start far lower than Everest’s summit. In fact, when trekkers first started going to Everest Base Camp, which is at “only” 17,600 feet, one in 50 died from high-altitude sicknesses. Even travelling from sea level to a mere 8,000 feet is enough to bring on Acute Mountain Sickness, the first stage of high-altitude illness. Lots of people have suffered from it, because it can be brought on by simply flying from a coastal city to mile-high Denver, then renting a car and driving up into the mountains. In fact, fully 75 percent of people suffer from at least mild symptoms of AMS at elevations over 10,000 feet. In mild cases, the symptoms include headache, dizziness, fatigue, shortness of breath, loss of appetite, nausea, disturbed sleep, and a general feeling of malaise. (The disturbed sleep is brought on by a pattern of breathing called Cheyne-Stokes Respirations–a few shallow breaths, followed by deep sighing respirations that fall of rapidly and may stop entirely, before resuming with shallow breaths again. Not surprisingly, when breathing stops, people tend to become restless and may wake up feeling like their suffocating, which isn’t exactly conducive to a good night’s sleep!)
In moderate cases, a severe headache that can’t be relieved by medication, vomiting, increasing weakness, shortness of breath and decreased coordination may develop, and in severe cases, sufferers can’t get their breath even when resting, can’t walk, and suffer fluid buildup in their lungs.
These symptoms are brought on by the body’s built-in response to the dropping air pressure, which include: an increase in the depth of respiration; increased pressure in pulmonary arteries, which forces blood into portions of the lung which aren’t normally used in thicker air; an increase in the production of red blood cells to carry oxygen; and the increased production of a particular enzyme that facilitates the release of oxygen from the blood to the tissues.
Avoiding these problems requires acclimatization, which means spending one to three days at a particular altitude. Once you’ve acclimatized to one altitude–say, 10,000 feet–you can climb higher. Then you have to rest again to acclimatize once more. To be safe, experts say, you need to increase sleeping altitude by no more than 1,000 feet a day. And, of course, if problems continue, you should descend to a lower altitude–preferably while you can still walk.
As noted, almost everyone suffers from at least a mild form of Acute Mountain Sickness even at relatively low altitudes. At extremely high altitudes, like the slopes of Everest above Base Camp, two even more serious forms of the illness can develop (although AMS itself can be quite deadly–loss of coordination is a really bad thing in a mountain climber), which mountaineers refer to by their acronyms: HAPE and HACE.
HAPE stands for High Altitude Pulmonary Edema, and results from a build-up of fluid in the lungs. This is a side-effect of the way the body increases blood pressure to try to get more oxygen to its tissues–the high pressure causes fluid to leak from the capillaries. The build-up of fluid makes it harder and harder for oxygen to get into the bloodstream. Symptoms include shortness of breath even at rest, tightness in the chest, fatigue, a feeling of impending suffocation at night, weakness, and a persistent cough bringing up white, watery or frothy fluid. Immediate descent to lower altitudes (and from there to a hospital) is the only treatment; otherwise, as one climber put it
HACE is even scarier: it stands for High Altitude Cerebral Edema, and is caused by the swelling of brain tissue due to fluid leaking from the capillaries. Symptoms include headache, loss of coordination, weakness, and decreasing levels of consciousness, which can include disorientation, loss of memory, hallucinations, psychotic behavior, coma and, in severe cases, death. (In climber Charles Corfield’s vivid words, “the brain gets squeezed out down the hole for the spinal cord like toothpaste–and then you die.”) It usually takes a weak ore more at high altitude for this condition to develop. Again, the only treatment is immediate descent to a lower level.
AMS, HAPE and HACE aren’t the only problems faced by climbers at high altitudes. The increase in the number of red blood cells means blood grows thick and sludge-like, prone to clotting which, in turn, can lead to strokes, heart attacks and pulmonary embolisms. The “Khumbu Cough,” a dry, hacking cough that can be so bad that some climbers have broken ribs, is brought on by the drying out of the bronchi, caused by breathing cold, dry air. This also leads to dehydration, which means climbers need to drink plenty of water.
They also need to eat plenty of calories to keep up their strength an to enable their bodies to generate enough heat to ward off hypothermia and frostbite, but high altitude makes people feel so lousy they usually lose their appetites and have to force themselves to eat.
But in the end, the single most deadly problem faced is probably hypoxia: lack of oxygen in the brain. The brain, though it makes up only three percent of the body’s mass, uses 20 percent of the oxygen supply. When that supply grows short, it’s the brain that suffers most. Judgement is impaired. Not to put too fine a point on it, people grow stupid–and on Everest, they’re at their stupidest just when they’re in the greatest danger, in the Death Zone.
