At altitude

All air has 21% oxygen. At higher altitudes the barometric pressure is lower, so the effective oxygen is less.At sea level the pressure is 160 mm hg and we have all the use of the 21% of oxygen.

At 5,000 feet the pressure is 130 mm hg and we have the effective use of 17% oxygen. You will need to breath deeper.

At 10,000 feet the pressure is 110 mm hg and we have all the effective use of 14% oxygen, only two-thirds that of sea level. Besides needing to breath deeper, you may feel lightheaded or dizzy, very tired or get a headache.

Being in good physical shape unfortunately is not protective against high-altitude illnesses.

When we camp at Tuolumne Meadows, for example, we are staying at 8,600 plus feet elevation. Our hikes to the top of Mount Hoffman go to 10,850'. Below, Mount Hoffman as seen from Glacier Point:

You will probably feel out of breath at first and may even get a headache and lose appetite.

A mild headache is normal. If the headache is worse in the morning after a night's sleep you have trouble.

Shortness of breath when exerting yourself is normal. If it progresses to shortness of breath when resting, you have trouble.

Avoid eating high fat, high protein near bedtime at least the first night, stick with high carbo evening snacks. You may lose your appetitie, but you should eat. Sweet drinks are an ideal carbo supplement and water refill for people without an appetite.

Take it easy the first day.

Drinking lots of water helps.

Taking any kind of sleeping pills, which decrease respiratory rates, can make it worse.(This can include some kinds of allergy medications.) Alcohol or other depressants make it worse.

True acute mountain sickness is rare at Tuolumne Meadows or other 8,000 ish altitudes.

From the National Park service, incidence of high altitude sickness in various groups:

skiers who reached a maximum altitude of 11,500 feet, but who slept at 7,000 feet, 15-20% had Acute Mountain Sickness (AMS), who slept at 8,500 feet, 25% had AMS, at 10,000 feet 25-40% had AMS. Less than 1% had HAPE or HACE.

Mount Rainier climbers who took 1-2 days (they flew in, then climbed) to get to the peak, and who reached a maximum altitude of 14,405 feet but slept at 10,000 feet: 67% had AMS and less than 1% had HACE or HAPE.

Mt. Everest trekkers who flew in, slept at 10,000 to 17,000 feet and went to a maximum altitude of 18,000 feet: 47% had AMS and 1.6% had HAPE or HACE 1.6%. Those who took 10-13 days walking (same altitudes slept at and reached) 23% had AMS, 5% HAPE or HACE.

__________________________________________________

From the Yosemite Daily Report of July 1, 2004

According to the American Academy of Dermatology, sunburns develop more quickly at high altitudes. A study compared the sun's ultraviolet energy in three locations; Vail, Colorado; New York City; and Orlando, Florida. UVB rays were most powerful in Vail, the highest of the three locations. For each 1,000 feet of elevation, the intensity of ultraviolet light increases by 8 to 10 percent. In Vail, the potential to cause sunburn was less than half the time as in Orlando, even though Orlando is much closer to the equator.

Follow these tips to protect you from the suns damaging rays:

Use a broad-spectrum sunscreen with an SPF of at least 15 on all exposed skin, including the lips, even on cloudy days.

Apply sunscreens at least 30 minutes before going outside.

If exposed to water, either through swimming or sweating, a water-resistant sunscreen should be used.

Reapply sunscreen frequently - every 1 1/2 hours, more often if sunny or heavily perspiring.

Wear a broad-brimmed hat and sunglasses.

Seek shade whenever possible.

Wear protective, tightly-woven clothing.

Plan outdoor activities early or late in the day to avoid peak sunlight hours between 10 am and 4 pm" (Glenn Dean)

The De Anza Faculty advisor to the Outdoor Club is much more anal about sun protection and would advise that 15 SPF is not enough. Be sure to apply sunscreen to the underside of your chin, underside of and just up into your nose to protect from sun reflected off water or granite.

Some brands of sunscreen can be applied right before going into the water, but read the directions. Some will wash off and make an oil slick if you put them on less than twenty minutes before swimming.

__________________________________________________

In Medicine for Mountaineering, we find a discussion of sleep periodic breathing at high altitude.

"Is almost universal at altitudes above 13,200 feet and may occur at lower altitudes (above 6,600 feet). The typical pattern begins with a few shallow breaths, increases in depth to very deep, sighing respirations, then falls off rapidly. Respirations can cease for five seconds or more before shallow breaths resume and the pattern is repeated. An observer may fear that the person is not breathing at all.

"During the period when breathing has stopped, the person often becomes restless and sometimes awakens with a sense of suffocation...it is so common at high altitude that it should not be considered abnormal...however it may be a sign of a serious disorder if it occurs for the first time during an illness or after an injury, particularly a head injury."

__________________________________________________

Any hike to the top of peaks and domes must start early so we can get to the top and back down before expected afternoon lightning storms start. If at any point thunder is heard or lightning seen, you should turn back from the top of any peak, even if you haven't gotten as far as you wanted. Don't get zapped! Don't use your cell phone or IPod. Read Thunderstorm and lightning safety.

__________________________________________________

a test for Acute Mountain Sickness (AMS)

One of the scoring systems to determine if the altitude is getting to you (slow down a little for awhile) or realy getting to you (you need bedrest at a lower elevation), is the Lake Louise Acute Mountain Sickness (AMS) Score. It was developed for research, but can be used to give mountaineers a warning of trouble.

The only real first aid for Acute Mountain Sickness is to descend to a lower altitude.

Are you one of those people who ignores shivering(hypothermia) until it is severe? AMS can turn into life-threatening High Altitude Pulmonary Edema (fluid is leaking into your lungs) or High Altitude Cerebral Edema (your brain is swelling) quickly.

Don't be so brave and ignore other than mild symptoms.

Take this test:

Remember that the symptoms are quite the same as those of a hangover, intoxication or the flu, so rule these out first.

Self Report Questions:

Headache

0 No headache

1 Mild headache

2 Moderate headache

3 Severe, incapacitating headache

Gastrointestinal symptoms

0 No gastrointestinal symptoms

1 Poor appetite or nausea

2 Moderate nausea or vomiting

3 Severe, incapacitating N & V

Fatigue and/or weakness

0 Not tired or weak

1 Mild fatigue/ weakness

2 Moderate fatigue/weakness

3 Severe fatigue/ weakness, incapacitating

Dizziness / lightheadedness

0 Not dizzy

1 Mild dizzy

2 Moderate dizziness

3 Severe dizziness, incapacitating

Difficulty sleeping

0 Slept as well as usual

1 Did not sleep as well as usual

2 Woke many times, poor night's sleep

3 Could not sleep at all

What your score means:

If you recently went up in altitude from where you are used to (example, most Outdoor Club people live at around 400 feet altitude, but when we go to the Sierras or the Tetons we often travel starting at 8,000 feet altitude).

and if you have a headache

and at least one other symptom from the five groups above

and a total score of at least 3

(although some researchers say a score of 4 minimum), then you have AMS and you need to slow down.

Hikers, backpackers, climbers and other high country travelers usually use the five question test above.

These below are used more by researchers, but are of interest as well.

As you can tell by the symptoms, scores of 2s, 3s and 4s are big trouble that needs attention immediately.

Clinical Assessment:

Change in mental status

0 No change in mental status

1 Lethargy (sluggish) /lassitude (weariness of mind)

2 disoriented/confused

3 Stupor (mental apathy) / semi conscious

Ataxia (Loss of coordination of muscles, as judged by ability to walk heel-to-toe with eyes open. If you have any reason to doubt someone's ability to do this, have two people stand on either side of them as they try).

0 No ataxia

1 Maneuvers to maintain balance

2 Steps off line

3 Falls down

4 Can’t stand

Peripheral edema (such as swelling of hands or feet)

0 No peripheral edema

1 Peripheral edema in one location

2 Peripheral edema in two or more locations

__________________________________________________

In an article in the San Francisco Chronicle in 2003, Study changes attitude about altitude

"High altitude pulmonary edema (HAPE) is a serious, scary disease -- and one that doctors generally believed wasn't much of a problem for healthy people traveling to elevations below about 9,000 feet.

But a new study published last month in Chest, a journal devoted to cardiopulmonary and critical care, found the condition -- marked by fluid in the lungs and fatal if left untreated -- occurring as low as 5,000 feet above sea level. That's lower than Lake Tahoe, with an elevation of 6,229 feet. The findings suggest that what may have been diagnosed as pneumonia among skiers, snowboarders and other alpine visitors could actually be HAPE."

Read the whole article at:

http://sfgate.com/cgi-bin/article.cgi?file=/chronicle/archive/2003/02/16/TR221535.DTL

__________________________________________________

Want to read even more?

Travel At High Altitude http://www.medex.org.uk//medex_book/about_book.php

An Altitude Tutorial from the International Society for Mountain Medicine http://www.ismmed.org/np_altitude_tutorial.htm

__________________________________________________

see also:

http://www.nps.gov/yose/sar/hikesafe.htm

http://www.nps.gov/yose/sar/climbsafe.htm

GORP and hiking snacks

Thunderstorm and lightning safety includes the answer to the question: Why can't you swim during a lightning storm? A strike on a lake doesn't kill all the fish in the lake.

Hiking Advice has hot weather hiking advice, hiking logistics and the answer to the question: When is the best time of day to cross a mountain stream?

Yosemite trips index