What is High Altitude?
High Altitude is from 8,000 to 13,000 feet. This is common hiking elevation in western U.S.
Very High Altitude is 13,000 to 18,000 feet. Some hiking, mostly in high Rocky Mountains.
Extremely High Altitude is over 18,000 feet. Special breathing gear required.
Air is made up of nitrogen, oxygen, and argon with traces of other stuff in it. Nitrogen is about 78%, oxygen is 21%, and argon is 1% - those percentages stay constant no matter what the elevation.
Air pressure becomes less as you climb up a mountain, and less air pressure means less oxygen to breath. High altitude hiking is when you trek at an elevation that may affect your body. Some people are affected as low as 7000 feet. Let's take a minute to explain a bit about air pressure and available oxygen.
If you put your arms out and turn around, you've made a circle that is about 5 feet wide. Imagine that circle being a column of air going from the ground up, up, up to the edge of the atmosphere. From where you're standing, there are thousands and thousands of feet of air above you in your column. All the nitrogen, oxygen, and argon above you is pushing down on the air around you. The height of that column of air determines the air pressure where you are and that air pressure determines how densely the gas particles are packed together.
The higher you climb, the less air there is above you in the column, so the lower the air pressure and the less dense the gas. Every 1000 feet you climb, you lose about 3% of the available oxygen because there is less gas packed into your column of air. At 12,000 feet, every breath you take brings in only 2/3 the amount of oxygen that you would suck in at sea level.
Another important thing to keep in mind is that air temperature drops about 3.5 degrees for every 1000 feet of elevation gain. A nice 75 degree day at 5,000 feet will be more like 60 degrees at 10,000 feet.
Hiking at High Altitudes
As you expand your hiking adventures, you'll probably be driven to hike up higher and higher mountains. At some point, it becomes mountaineering, but there are many peaks over 14,000 feet that have trails all the way to the top. Colorado has many 14,000+ peaks that people make a goal of summiting.
As you climb ever higher, you need to understand the added risks and problems with higher altitudes. You will find yourself needing to breathe deeper and more often to keep enough oxygen circulating to your muscles. Every breath has less oxygen, so you need more breaths. There are more special preparations for higher altitude hiking:
Slower Pace - If you are not expecting the lack of oxygen, you will find yourself needing frequent rest stops to recover. But, by slowing your pace as you gain elevation, you will keep your body working without overexerting.
Even Rhythm - Maintaining a breathing/stepping rhythm is even more important at higher elevations than lower down. It will help keep you from overexerting yourself.
Deep Breathing - when you first notice any breathlessness, start thinking about your breathing. Take deeper breaths and smaller steps until you have a sustainable pace again. On steeper sections, deliberately placing each foot and taking a breath may be the way to go.
Sunscreen is critical because the sun is more powerful higher up. Snow, light-colored rocks, cool temperature, and no shade above treeline also contribute to easy sun burns.
Sunglasses will help prevent squinting and headaches. Snowblindness and sunburned eyelids are real problems. Use side guards on your glasses for more protection.
Extra Clothes - long sleeves, long pants, hats, and gloves to protect from the sun, wind, and cold. Weather can change in a heartbeat, easily dropping more than 30 degrees in 1/2 hour or less.
Ignoring the risks of hiking at higher elevations will ruin your day. If you're lucky, you'll just be wiped out, but there's a good chance you can get yourself in deep trouble.
Altitude Sickness
Everyone needs to breathe more when they are at altitude. But, some people become sick when they hike too high. It just happens.
The biggest problem with hikers is that they want to reach their goal and may not accept that they need to stop when problems occur. Being honest enough to stop and possibly turn back can be a very difficult step to take.
There are many factors that come into play when altitude sickness hits, but taking some steps will help minimize your risk:
Acclimatize - The biggest contributor to altitude sickness is climbing too fast. That means the person in good shape has a good chance of getting sick since he tends to push harder and hike faster. People that reside at lower elevations will experience a greater change at lower heights. To acclimatize:
Rest and relax for 2 hours for every 1000 feet the trailhead is above your normal elevation. For example, if you live in Iowa at 1,000 feet and plan to hike in Wyoming at 9,000 feet, you should arrive in the afternoon and start your hike in the morning after sleeping a night to acclimatize.
Climb slowly and steadily.
Check how you are feeling every hour. Nausea, lack of hunger or thirst, headache, dizziness, difficult breathing, lack of coordination are all warning signs.
On multi-day hikes, sleep no more than 1500 feet higher than the previous night. You can climb higher during the day, but come down to sleep.
Expect It - just because you went to 14,000 feet last summer does not mean your hike to 12,000 feet will not affect you next weekend. Any height over 8,000 feet should make you be on the alert. Every hike is a new experience and by being on the lookout for symptoms, you will catch problems early on.
Hydrate - drinking more water helps reduce the symptoms. Drink even if you do not feel thirsty.
Reduce Exertion - the harder you push your body, the greater your risk of getting symptoms.
Eat Well - eat a high carbohydrate menu, and don't forget to drink water.
AMS - Acute Mountain Sickness
About 75% of people that hike over 10,000 feet will experience some mild AMS symptoms. Hikers can continue on with mild symptoms, but if they do not subside or they get worse, then corrective action is required. The problem with AMS is that its symptoms are similar to other common hiking problems such as dehydration, fatigue, and eating bad food.
Ignoring these symptoms can result in extreme situations, possibly death. Ordered from most severe to least:
Disorientation - confusion, hallucinations, irrational behavior can all be caused by edema, which is swelling of tissue and can be caused by higher elevation.
Loss of Coordination - someone stumbling or dropping their water bottle should be signals. If you suspect someone may be experiencing this, test them:
Have him walk heel-to-toe in a straight line.
Have him stand straight with feet together and arms at sides and then close his eyes. He should be able to balance for at least 15 seconds.
Lassitude - similar to exhaustion, just being tired out. After eating and drinking water and resting, exhaustion should go away. If it does not get better, do not go on and keep resting. There will be no energy to eat, talk, or do anything as the situation worsens.
Headache - there are many causes for a headache, from bright sun to altitude sickness. If a headache does not go away after food, water, and rest, then suspect altitude sickness.
Nausea - upset stomach and loss of appetite.
HAPE - High Altitude Pulmonary Edema
High Altitude Pulmonary Edema is excess fluid in the lungs which further reduces oxygen exchange from air to your body. The level of oxygen diminishes which can lead to impaired thinking and ultimately death. HAPE symptoms include shortness of breath while at rest, feeling of tightness in the chest, weakness, feeling of suffocating, persistent cough, and fatigue. The person may also cough up watery fluid.
HACE - High Altitude Cerebral Edema
High Altitude Cerebral Edema is excess fluid in the brain which puts pressure on the brain. This usually develops over a few days but is a life-threatening situation. Disorientation and weird behavior will lead to unconsciousness most likely followed by death if nothing is done.
Treating Altitude Sickness
The important thing to do is stay alert and catch early symptoms fast. The longer symptoms develop, the more drastic the response will need to be. Assuming you catch the symptoms early, follow these steps - but if the symptoms are advanced, decide between the last couple steps:
Rest - take a break and take in some fluids and food. Take aspirin for headache. Do not be in a hurry and plan to break for an hour to give the symptoms a chance to recede.
Medicate - Diamox is an altitude medication that may help.
Descend - Drop at least 1,500 feet down the mountain and rest.
Halt - Stop the hike and descend completely off the mountain.
9-1-1 - Call for medical services. If the victim can hike, start descending immediately, not in the morning or after supper, now! Otherwise, wait for evacuation. |
发表于 2009-4-13 19:55:49
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