Altitude a Major Challenge to Climbers

Brian Handwerk
for National Geographic News
May 14, 2002
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The National Geographic 50th Anniversary Everest Expedition commemorates the first ascent of the world's highest mountain, by Edmund Hillary and Tenzing Norgay in May 1953. It also honors the first Americans to stand on the top of the world, including Barry Bishop, in 1963.

The sons of Everest pioneers Hillary, Norgay, and Bishop—Peter Hillary, Jamling Norgay, and Brent Bishop—are helping make a documentary that will air on the National Geographic Channel in the United States and internationally in 2003.

The National Geographic 50th Anniversary Everest Expedition is made possible in part by the generous support of American International Group, Inc.

The margin of safety is razor-thin on a mountain like Mount Everest. Some hazards, such as thundering avalanches, freak storms, and hidden crevasses are beyond a climber's control.

But many deaths and near-death experiences are the result of human errors brought about or compounded by the effects of high altitude. Climbers are vulnerable to altitude sickness once they climb above 8,000 feet (2,400 meters). The region above 25,000 feet (7,600 meters) is called the death zone. 

Climbers who venture into this zone cannot escape the potentially deadly effects of oxygen deprivation; they can only attempt to minimize and control what breathing the thin air at high altitudes does to their bodies.

Everest's "Thin Air"

Air, whether at the summit of Mount Everest or at sea level, contains about 21 percent oxygen. But at high altitudes, the density of air changes—it becomes thin. Thin air is not nearly as rich in oxygen as the dense, more heavily compressed air found at sea level.

At the top of Mount Everest, more than 29,000 feet (8,840 meters) above sea level, the atmospheric pressure is about one-third that of sea level. Climber and filmmaker David Breashears has described climbing at such altitudes, even with bottled oxygen, as equivalent to "running on a treadmill and breathing through a straw."

For reasons not entirely understood, each person reacts differently to high altitude. On mountains as high as Everest, however, no one is immune.

The first effect a climber will notice upon reaching higher altitudes is an increased breathing rate. Any exertion, even eating a meal or crawling into a sleeping bag, leaves climbers short of breath.

The heart rate also soars, as high as 140 beats per minute, and blood thickens, increasing the possibility of clotting or strokes. These physical reactions are the body's way of combating oxygen deprivation, also known as hypoxia.

Altitude affects all aspects of the climber's life up high. Loss of appetite is a common and potentially dangerous occurrence since it is essential that climbers remain nourished and hydrated. Getting enough sleep can also be a problem, as most people battle insomnia or find they wake frequently during the night.

These troublesome effects, while unpleasant, are rarely life threatening. But as the climber goes higher, the air gets thinner, and hypoxia can quickly escalate and lead to far more dangerous medical conditions: High-Altitude Pulmonary Edema (HAPE) and High-Altitude Cerebral Edema (HACE).

Pulsating Teapots

HAPE is characterized by the accumulation of fluids in the lungs. The condition gets worse with increasing altitude. Unless the victim descends to lower altitudes quickly, he or she will literally drown in his or her own internal fluids.

HACE occurs when the body, struggling to get enough oxygen, compensates by increasing blood circulation; this can cause the brain to swell. The loss of coordination and mental deterioration—including hallucinations—that occur with HACE can quickly create dangerous situations.

Climbers suffering from acute mountain sickness have been known to chat with imaginary companions, see strange visions, and lose touch with reality. Some have removed their clothing as they froze to death in high-altitude bivouacs. As long ago as 1933, Frank Smythe reported seeing strange pulsating objects hovering in the air. Teammates jokingly referred to them as "Frank's pulsating teapots," but such dementia is rarely a laughing matter.

As climber and altitude expert Charles S. Houston explained in Everest: Mountain Without Mercy, HACE "weakens the higher functions of the brain—judgment, perception, memory, and will. Many high-altitude tragedies have been caused by the dulling of these faculties. Near the summit of Everest, every climber is in significant danger; at a time when clear thinking is critical, climbers are most impaired."

Breathing Bottled Oxygen

A person magically transported from sea level to the summit of Everest would lose consciousness nearly immediately and die a short time later. Yet climbers are able to spend a lot of time at high elevations. How do they do it?

The old adage "climb high, sleep low" tells the story. Climbers gradually acclimatize their bodies to the thinner air at higher elevations by making incrementally increasing forays to higher altitudes, often carrying loads to establish high camps, then returning to lower elevations to sleep. But above around 24,000 feet (7,000 meters), most climbers rely on bottled oxygen.

In fact, when climbers first began tackling Everest, scientists were unsure whether humans could survive at the summit without oxygen.

Reinhold Messner and Peter Habeler made the first oxygen-free ascent in 1978. Since then, an increasing number of elite climbers who believe nothing should come between a climber and the mountain have attempted to summit Everest without oxygen. However, the vast majority of climbers, past and present, would be unable to survive high on the mountain without bottled gas.

Bottled oxygen provides a much-needed performance boost, helps climbers sleep, retain mental clarity, and resist the mountain's fierce cold. But it also adds one more thing to the list of what can potentially go wrong. When equipment malfunctions or bottles run out, oxygen deprivation can have catastrophic consequences for climbers who suddenly find themselves high on the mountain and without the precious gas.

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