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Altitude Adaptation And Acute Mountain Sickness

© 2006, D.M. Polaner



Altitude Adaptation And Acute Mountain Sickness

a brief (well, maybe not so brief) guide for the worried flatlander

Many people who live at or near sea level have posted queries on the board regarding things like:

  • Am I going to get sick when I come up to Breckenridge?
  • The last time I was in Vail I had a splitting headache and vomited my guts out for 24 hours- is there anything I can do this time to keep from getting sick?
  • My brother in law said if I drink gingko tea I will not be sick- is this true?
  • Altitude sickness is a bunch of hooey- it only affects people climbing over 15,000ft (4700m). Don’t worry about it.
  • I have asthma (or heart disease, or emphysema, or morbid obesity, or hemorrhoids, or…) - do I need to worry when I come up to Jackson Hole?
  • I heard that if I have any alcohol up there it will have twice the effect as at sea level. Will I be able to finish a whole bottle of Jaegermeister in one sitting? Well Wear the Fox Hat think I am a wimp?

In this thread I will give an explanation of what acute mountain sickness (AMS) is, what the risks are, what you may be able to do to prevent it, and dispel some of the myths about it. I will also describe very briefly how one acclimates to altitude, and some facts about acclimatization and performance at altitude. There are some links to good web sites about altitude medicine at the end.

Who I am-
I came upon the EpicSki forums about 3½ years ago and have been hanging around ever since (far too much, according to my wife, who is probably right). I am a physician on the faculty at the University of Colorado School of Medicine, and have a long-standing interest in pulmonary physiology and altitude medicine.

What happens at altitude and why?
Altitude sickness doesn’t occur below 5000ft, and usually doesn’t develop until you ascent rapidly to more than 7500ft. The speed of ascent is important- going rapidly is much more likely to result in symptoms than ascending gradually.

At high altitude and low barometric pressure, there is less oxygen in the air (remember Boyle’s Law?), so each breath you take results in less oxygen being transferred into the blood by the lungs. (There is also some evidence that the lower barometric pressure itself as well as the low oxygen levels may play a role in AMS, too, but that is beyond the scope of this discussion.) With lower oxygen levels in the blood, there is less oxygen available to the tissues for metabolic needs. Thankfully, your body has some rather clever methods for dealing with this, otherwise we would all be stuck water skiing at sea level.

The first adaptation actually begins within minutes or hours of ascent- an increase in respiratory rate (more volume of air breathed each minute= more oxygen transferred to the blood each minute). This is why you feel short of breath. The magnitude and efficacy of this response is genetically predetermined for each individual. This reaches maximum response in about 4-7 days.

Your heart rate also increases within a day of ascent, pumping more blood (and therefore more oxygen) to the tissues. As other mechanisms kick in and you develop long-term acclimatization, your heart rate returns towards baseline.

It takes about a week for your body to begin to make more red blood cells to increase oxygen carrying capacity. By about 3-4 weeks, the increased red blood cell concentration in the blood has stabilized. Of course, you need enough iron in your diet for this to work. There is also a change in the ability of the red cells to pick up and off-load oxygen. This begins about 72 hours after ascent, and takes a few more days to fully kick in.

What is AMS?
Acute mountain sickness is a constellation of disorders caused by acute exposure to low pressure and low oxygen levels. It appears to be caused by swelling of the brain- a mild form of HACE (see below). Diagnosis (by the Lake Louise Criteria, which were formulated at the Hypoxia Symposium there a number of years ago) requires the presence of headache and one or more of the following:

  • GI symptoms (nausea, loss of appetite)
  • Fatigue or weakness
  • dizziness or lightheadedness
  • difficulty sleeping

A large study in Colorado found that 25% of people from low altitude ascending rapidly and sleeping at 8200ft (2500m) will develop AMS. These people may feel lousy for short while, but most of them will get better in a few days and not get sicker. About 1%, however, will develop more severe illness- high altitude cerebral edema (HACE, or brain swelling) or high altitude pulmonary edema (HAPE, or high blood pressure and fluid in the lungs). Both of these are life-threatening emergencies, and require immediate medical attention and descent if at all possible.

Other common problems at altitude
Dehydration- the air is dryer up here (due to the lower barometric pressure) and you breathe faster, so you lose a lot of body water in your breath. You also pee more when you ascend (high altitude diuresis), so there are several sources of body water loss that must be accounted for. Drink a lot! Drink more than you think you need, but also make sure that you have adequate salt and potassium in your diet.
The sun is strong up here- and the atmosphere is thinner, so there is less filtering of UV which can cause both sunburn and snow blindness - don’t underestimate this! Wear sunscreen even when it is cloudy, and wear sunglasses or goggles with UV protection.

Myths and truths about altitude:

  • If you are in great shape you will acclimate better.

Not true- fitness does not alter the incidence of AMS at all. Fitness does, however, improve athletic performance at altitude (just like it does at sea level!). You should not expect, however, that you will be able to achieve the same level of performance until you acclimate- your tissues don’t have as much oxygen available. I certainly highly recommend getting in the best shape you can so you can ski better, be less sore and less fatigued, etc., but it will not alter your risk of AMS.

  • You are a victim of your genes- if you have the right genes, you will acclimate well, otherwise…well, maybe surfing is the sport for you.

Only partly true- there is a genetic component to the ability to acclimate effectively and quickly. But most people can acclimate; it is just harder and takes more time for some.

  • People born up there are different, and those of us born in flatland will never measure up.

Partly true, again- people born at altitude may always have some edge. The reasons for this are not clear, but there are plenty of people born at or near sea level that do pretty well at altitude anyway. Ed Viesturs, who has climbed all 8000m peaks without supplemental oxygen, was born in the Midwest. So was Tom Hornbein, the first person to climb the West Ridge of Everest. The list of high altitude climbers from flatland is pretty long.

  • Alcohol has increased effect up here- you get drunk much easier at altitude.

Not true- good news or bad news, depending on your perspective (you can drink as much as you do at home, but it’s not cheaper to get drunk). There is evidence, however, that alcohol intake may slow your adaptation to altitude, and it is a diuretic (it makes you pee), so it can increase the risk of dehydration, which is a problem at altitude. Alcohol also decreases your breathing rate and respiratory responses, thereby blunting one of the most critical early mechanisms of adaptation. It is probably wise to limit alcohol intake for the first few days at altitude.

  • I got sick before; am I doomed to be sick every time I go above 7000ft?

Well, maybe- this one is hard to answer. There are some people who are just more likely to have altitude sickness, and are slower to acclimate. Some of this risk is genetically determined- there are good adapters and poor adapters. One time may not mean anything more than bad luck, but if it is a repeated problem every time you ascend, you are a candidate for prophylaxis (see below).

  • My head is killing me- is this AMS?

Possibly. It is wise to consider it AMS until you prove it is not. Dehydration is the other big cause of headache at altitude. If you rehydrate well, and the headache goes away, it was probably not AMS. If not, you probably have AMS.

  • I just can’t sleep well up here- should I try a sleeping pill?

NO!! The reason that you don’t sleep well is because of an abnormality in your breathing that occurs at altitude called Cheynes-Stokes respiration- alternating periods of deep and shallow breathing. This interferes you’re your ability to fall into a deep sleep, and during the shallow periods you may even wake completely feeling short of breath. The best treatment for this is Diamox (see below). Using drugs that can decrease respiration can make you sicker.

  • I am a smoker- is this a problem?

Well of course it’s a problem! Smoking is really, really bad for you (did you expect me to say anything else?). But it has a number of particularly bad effects at altitude. Smokers have increased levels of carbon monoxide in their blood, which interferes with the function of red blood cells to carry oxygen. Nicotine constricts your blood vessels, so you will have less blood flow to your extremities. Even if you think you do fine at altitude while smoking, you will do better if you don’t.

  • Don’t drink caffeine.

Not true- there isn’t any relationship between caffeine intake and either AMS or impaired acclimatization. However, caffeine is a diuretic, and if you drink caffeine you must be more watchful of your fluid intake to compensate for what you pee out.

  • Drink lots of fluids and you will not get AMS.

Not really- it IS important to drink more than usual at altitude because you get dehydrated easily. But that is not the same as AMS, and the relationship between the two is far from direct. You can get quite sick at altitude from dehydration, but if you feel better after rehydrating, your headache was probably not AMS.

Is there anything I can do to enhance acclimatization?

  • The first, best, and most obvious thing is graded ascent. If you can, come up slowly- spend a night in Denver or Salt Lake City before going up to the resort. This, of course, is not always practical, but may be an option for some.
  • Limit exertion on the first day out.
  • Don’t smoke!
  • There is some evidence that a high carbohydrate diet beginning about 3 days before ascent may speed acclimatization.
  • Climb high, sleep low. This old climber’s maxim makes a lot of sense, especially since sleep disordered breathing is a common manifestation of AMS, and AMS is often worse during sleep. If you are prone to AMS, you may feel better at a resort with a lower base elevation.
  • Avoid alcohol for the first few days.

If you have had consistent, repeated problems with altitude sickness, you may be a candidate for prophylactic (preventive) therapy. You should discuss this with your doctor. There is one medication proven to help acclimate to altitude and one that is controversial.
The proven one is acetazolamide (Diamox). It works mostly by mimicking and enhancing the body’s respiratory adaptive mechanisms, and should be started a day in advance of ascent. It can also reduce the symptoms of AMS once it develops, but should not be relied upon for treating anything more than mild disease- particularly sleep disturbances. It has several mildly unpleasant potential side effects- it causes tingling in the lips, hands and feet, and makes carbonated beverages taste bad. It is a diuretic, so you need to increase fluid intake. It is about 75% effective at preventing AMS during rapid ascent. It cannot be used by people with true sulfa drug allergies.
Gingko biloba is an herbal preparation that has been shown in some studies- but not in others- to reduce the incidence of AMS by about 50%. It has not been shown to be effective for treating AMS once it has developed. The jury is still out on this, because of the conflicting data in the literature, although it may be effective in some circumstances for some people, and may be worth a try. The dose is 120mg twice a day starting 5 days before ascent. One problem is that herbal preparations are not regulated by the FDA, so standardization of what you are actually getting from brand to brand is virtually non-existent.

Good web sites for more information:
-International Society for Mountain Medicine. An excellent tutorial for the layman on AMS is available here (click on Mountain Medicine Information Center), as well as links to journals, abstracts and other scientific information.
- excellent site by Thomas Dietz, MD, although it has not been recently updated, and a few of the links are broken
-shameless plug for some of the interesting things that we do here at the CO Center for Altitude Medicine and Physiology

© 2006, D.M. Polaner

Comments (2)

I have questions rather than a comment:
Inasmuch as both are carbonic anhydrase inhibitors, would topirimate (Topimax) work for AMS in the same manner as does acetazolamide (Diamox)? It is not approved for this use, and, as far as I know, there are no studies on its efficacy for AMS, but one would think . . .
Further, What dose of Diamox do you prescribe? I have found that 250mg q 12 hours is sometimes needed, 125 mg often being inadequate for relief of symptoms. What has been your experience?
And lastly (funny that I have never wondered about this before) what is the incidence of AMS in children? Are they less prone? I don't believe I have ever known of a child disabled by its symptoms, but then, I have never been practicing in a setting where this would have occurred. If it is a problem, is the use of acetazolamide appropriate in kids, and at what age/dose?
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