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The Physiology of High Altitude Climbing
[JUST THE FACTS]

	Precious oxygen

What happens to your body at high altitude? Why do some people get sick and even die? According to Dr. Eric Weiss, when trekkers first started to going to Everest, one out of every 50 died. Nowadays, thanks to awareness of the consequences of high altitude, that figure is one in 10,000 to 50,000. The medical syndromes encountered at altitude all come down to the body's response to the decline of oxygen pressure.

Atmospheric pressure is a gauge of how many oxygen molecules are available per given volume, say a breath. While there is the same percentage of oxygen in the air up high, lower atmospheric pressure at higher altitudes means fewer oxygen molecules are available with each breath.

Cerebral Edema
Many people who travel from sea level to over 8,000 feet report symptoms ranging from headache to loss of appetite and nausea. Why? As the available oxygen falls, the body responds by increasing the blood flow to the brain, but it can overcompensate, and fluid leaks from the blood vessels into the brain causing it to swell. The result is Acute Mountain Sickness. Cases can run the spectrum from mild to life threateningly severe swelling called High Altitude Cerebral Edema (HACE).

Not surprisingly, the greater the elevation gain, the more severe the swelling. In severe cases the brain can get squeezed down the spinal cord which results in death. The way to avoid falling victim is to ascend gradually, about 1,000'/day over 8,000' which gives your body time to acclimatize properly.

You can treat, and indeed preempt, Acute Mountain Sickness by using a diuretic called Diamox and drinking plenty of water. Signs to watch for with HACE are persistent severe headache, loss of coordination, and problems with thought processes. Treatment is immediate descent, and Decadron or oxygen if available.

Pulmonary Edema
Groups of trekkers are occasionally struck by a mysterious flu-like illness near the high point of their trek, and, just as mysteriously, they get better when they head down. What they had was not flu, but High Altitude Pulmonary Edema (HAPE), which is a build-up of fluid in the lungs, and can lead to a feeling of profound fatigue.

As the body tries to get as much oxygen from the air as it can, Pulmonary edema can result from the greatly increased blood flow through the lungs. The heart increases the flow by increasing the pressure, causing leakage from the blood vessels into the air sacs. It usually takes a few days to develop, and is exacerbated by overexertion. In bad cases, you can hear a gurgling of fluid in the lungs, and the victim brings up a bloody sputum. This is a serious condition which can kill in only a matter of hours. HAPE is best avoided by gradual ascent. Treatment is immediate descent by several thousand feet and oxygen if available.

Too Much of a Good Thing
The body also responds to the lower oxygen levels by putting more red blood cells into circulation. Up to a point, this is a good thing. However, if it goes too far, the blood becomes thick and prone to clotting. Clots which get dislodged float around and can cause strokes, heart attacks, and pulmonary embolisms. The only treatment for thick blood is to be bled. Since this condition takes weeks to develop, it is rarely an issue, except on the Himalayan giants.

Many climbers who have been to over 14,000' have experienced listening to their tent-mates repeatedly stop breathing, gasp, breathe heavily for a while and then stop breathing again. This is called periodic breathing, and is caused when the system which regulates breathing gets out of whack. The sleeper responds to a build-up in carbon dioxide by hyperventilating. This leads to respiratory alkalosis, and the breathing center responds by shutting off respiration. CO² levels then increase and the cycle repeats. It is a relatively benign condition, and responds well to a low dose of Diamox taken at bed time.

The Khumbu Cough
A common complaint of high altitude climbers is a persistent dry cough (high altitude hack), which can be so bad it results in broken ribs. This condition results from a drying out of the bronchi caused by breathing the cold, dry air. The best prophylaxis is to avoid overexertion, thereby keep the breathing rate down, so that the bronchial mucosa stay moist.

If you would like to pursue high altitude medical topics further, check out Medicine for Mountaineering by James Wilkerson and "Wilderness Medicine, Ch.1, by Auerbach.

— Charles Corfield, Climber, 1998 Everest Expedition

JUST THE FACTS
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	oxygen system

• The concentration (percentage) of oxygen in the air is the same at all altitudes.

• The amount of oxygen available to the human body is determined by atmospheric pressure which decreases with altitude — the air thins leaving fewer molecules of oxygen per breath.

• Atmospheric pressure determines how much air is "pushed" into the lungs with each breath.

• The atmospheric pressure at the summit of Mount Everest (29,035') is about a third that of sea level.

• Heartbeat rate, breathing rate, and the production of red blood cells, which carry oxygen through the body, increase as the body acclimates to high altitude, allowing more oxygen to be "grabbed" from every breath.

Acute Mountain Sickness (AMS)

Often occurs around 8,000'

Symptoms:
• Vomiting
• Headache that doesn't respond to usual medicine
• Shortness of breath
• Exhaustion that doesn't fade with rest

This may be a warning sign for the onset of more serious altitude illness.

Treatment is rest with further ascent recommended only after symptoms have ceased.

Severe AMS

• Altered balance or muscular coordination
• Altered mental state
• Extreme shortness of breath with almost any activity
• Person is angry, combative, or incomprehensible

Further ascent is not recommended unless there are options for easy and rapid descent should symptoms recur.

HACE Symptoms

Has occurred as low as 10,000'

• Ataxia or loss of balance and muscle coordination
• Decreased mental functioning
• Severe headache
• Nausea and vomiting
• Hallucinations or stroke-like symptoms of impaired speech

Coma and death may rapidly follow. The only treatment is immediate descent.

HAPE Symptoms

Rarely occurs below 8,000'

• Extreme difficulty breathing and inability to catch one's breath
• Very rapid pulse and breathing rate (over thirty breaths per minute)
• Extreme exhaustion and difficulty with any exertion
• Coughing which may progress to sounding bubbly as lungs fill with fluid
• Fever and blue coloring, especially the lips and fingernail beds

Death can come on quickly. The only treatment is immediate descent.

Acclimating

• Climb as high as you want during the day, but raise sleeping altitude by no more that 1,000' a day.
• Factor in a rest day every 3,000'.
• Spend at least one night below 10,000' before ascending higher.
• If you don't feel good, don't raise sleeping altitude until you feel better.
• If you don't feel better at the current sleeping altitude, descend to below where you first felt sick.

Facts taken from Stephen Bezruchka's Altitude Sickness: Prevention and Treatment, with permission from The Mountaineers, Seattle, WA.

Altitude Illness: Prevention and Treatment
by Stephen Bezruchka, M.D.
Symptoms, treatment, and acclimatization strategy for high altitudes. Pocket size; paperback.