Wednesday, February 3, 2010

Understanding Altitude Sickness

I originally posted this on the socalhikes blog but this is a more appropriate home for it.

Background: You want to hike Mt. Whitney (~ 14,500 ft), the tallest peak in the contiguous United States. Or you may want to ascend other high peaks in the Sierras, or elsewhere.

Perception: This is the hardest hike you will do, therefore you need to train for it. I have heard this many times.

Reality: The hike certainly is a biggie (~ 22 - 24 miles, 6500 ft gain), but there are many other hikes that have more stringent cardiovascular conditioning demands. In fact, the main trail up to Mt. Whitney is not very steep.

What makes Mt. Whitney difficult is the altitude and the low pressure of oxygen.

Problem: Cardiovascular training does not improve a person's ability to handle low altitude, so how else can we adapt?


First, we need to understand what exactly is the problem with hiking up to high altitudes. A good discussion of these problems can be found here. The problem is that at increasing altitudes, the atmospheric pressure decreases. Atmospheric pressure is used to get air into our lungs and then into our blood. There is a pressure gradient, with lower pressure in the blood than the lungs, and lower in the lungs than in the air.

As the air pressure decreases, less oxygen will go into the lungs. Normally, we have certain breathing patterns that are based on having certain oxygen pressure in the air. If there is now less oxygen but we breathe with the same rate, we will not get enough oxygen into our body to use for energy. This is called hypoxia.

Less oxygen means less energy, and if nothing else changes, we will have to move slower. Luckily, the body realizes that we need more oxygen, and begins to breathe deeper and more frequently. This allows for more oxygen to get to the blood. Sounds good right? The problem is, this phenomenon is also known as hyperventilation and has its own side effects including making our blood alkaline (opposite of acidic) and makes us lightheaded and gives us tingling sensations.

So if we start hiking up to high altitudes, our body will start hyperventilating, but only so much so quickly. Lots of hyperventilization will worsen those side effects, which we don't want. But if we don't breath more, we won't get enough oxygen and will have to slow down. And lead to altitude sickness.

The Whitney area is beautiful. Take your time and enjoy it!

How do we prevent this crap from occurring? Well, it is known that fitness level does not affect chances of getting altitude sickness. This is why the common thought of "training for Whitney" is flawed as it won't tackle the real problems of dealing with altitude. In theory, my conditioning is such that I could ascend Whitney in 3 hours if it was at low elevations, but I took 6 and still felt like crap. Certainly I wasn't challenged in the normal conditioning sense.

The time proven way to prevent it is to only ascend 1000 ft a day...ha! This gives you time to acclimate - time to let the body get used to hyperventilation. But there is obviously a large elephant standing in the room, no one wants to ascend only 1,000 ft a day on a hike, it would just take too long. But that is the best way to avoid issues with altitude (and enjoy nature).

How else? Some people take a drug known as diamox, which basically works by making your blood more acidic and therefore stimulates hyperventilation to balance the blood pH. So this lets you hyperventilate without such strong side effects of hyperventilation, and therefore allows you to take in more oxygen.

But who wants to take drugs? Shouldn't there be a more natural way to adapt and 'train' for high altitude hiking? I think so. It is of my opinion that it would make sense to practice hyperventilating for several days before the big hike. This allows for the body to "acclimate" to the change in pH in the blood by adjusting how much CO2 and bicarbonate it allows in the blood. By the time you really need to hyperventilate, your body will be able to do so with less side effects.

Ascending too fast can make you feel sick!

This seems somewhat odd but basically this is what short term acclimatization is...getting used to hyperventilating. You can get used to hyperventilating at altitude (multi-day excursions with gradual increases in altitude) or consciously force yourself to get used to it. You won't have the hypoxia to stimulate the hyperventilation, so you'd have to do it yourself.

One of these choices should be made, otherwise you may come down with some serious acute mountain sickness (AMS). Throwing up on the top of Mt. Whitney (me) is not a good sign!

Keep in mind, hydration and consumption of carbohydrates are also important in helping your hiking performance at altitude. High altitudes suck even more water out of us, so we need to drink even more than normal. But this doesn't mean hydration will do anything to change the hypoxia/hyperventilation issue; it just means that dehydration due to altitude will make you feel even crappier - lethargic, headaches, etc...

Carbohydrates are needed because when there is less oxygen, our bodies will uses glycolysis (burning of carbohydrate storages) for energy. If we run out of those storages, we will move slower and have less energy. Not good!

Hopefully these thoughts provide some tips and thought provocation on how to deal with hiking at altitude. I have looked over journal articles and other sites to educate on this, but certainly do not have the issue down pat. Please let me know your thoughts.


  1. Hi Ze, I know someone who believes we need to learn how to use less oxygen. Like a whale that holds it's breath for long periods of time, when can also stimulate the body to figure out other ways to sustain the energy cycle with less oxygen (aerobic, anaerobic). I can look for the web-site if you're interested. Bob

  2. Hi Bob, I agree but perhaps with a little different twist. As I'll eventually write up, using more anaerobic energy isn't the answer because of it's limited storage. But perhaps limiting oxygen could stimulate more efficient anaerobic glycolysis, I'd have to look that up in pubmed but never heard anything like that.

    Otherwise, you are right using less oxygen is the key. The best way to do that is reduce your metabolic rate. There are those people who can stay under water for long periods of time (10 min, 30 min? I forget), because they are able to reduce heartrate and metabolism. Time to do some meditation!

  3. Ze,

    I've had some freedive training and the focus there is to use as little oxygen as possible. This is done by calming all non-essential functions.

    For hiking I can see the correlation. I like hiking poles for steep downhill and big steps uphill. Generally though I don't use them uphill. My legs are plenty strong to propel me up the mountain- it's my heart/lung/energy delivery system that is the limiting factor. Using poles takes more oxygen than not using them.


  4. Hi Jim,

    I agree. So how long can you freedive without surfacing for air?

  5. On summit day on Aconcagua I was suffering from the effects of hyperventilating to the point that it scared me. Mostly because I didn't understand at the time exactly what was happening - tingling arms, light headed, etc. It happened to me again on Vinson thought not quite as severely. On both those climbs I felt like I hadn't had time to properly acclimatize. When I headed to Manaslu two years ago I was very concerned about the possibility of it happening again but found it was a non issue. The same with my summit of Everest last year - not a problem. The only thing I can attribute this to is the much longer acclimatization process I went through on these two climbs.

    I guess what I'm saying is that even though I'm sure I was hyperventilating on the two Himalayan climbs, acclimatizing adequately prevented me from feeling the negative effects. Haven't tried trying to jump start the process by hyperventilating at low altitudes prior to the climb but it does seem logical that it could have some benefit.

  6. Ze,

    I'm way out of training and haven't been diving in over a year. A couple years ago in a class I made 4:15 floating in a pool. In the ocean, diving down through the kelp I'm really only good for about a minute.


  7. Hi Ze,

    very interesting idea about hyperventilation exercise before going to high altitude. Did you get some results with this idea (it is now August and you posted it on Feb)?

    Btw. another "solution" for this problem. I've heard that donating blood before going to mountains can also speed up your "acclimatisation". thought I didn't see any scientific results and I found it very odd. Certainly I am not planning to be a guinea pig. But have you heard about anything like that?


  8. Hi Peter,

    I have not attempted my hypothesis! I probably should have last week though...I wonder if there is a way to force yourself to practice hyperventilating, like breathing out of a paper bag?

    Very interesting about the blood donation, I have not heard about in reference to acclimatization, but I think it makes sense. Blood dopers in endurance sports take out some blood, allow new red blood cells to generate in place, then re-inject what was taken out. In effect, this increase the red blood cell count and increases oxygen binding. I am going to look this up on Pubmed!

  9. Hi Ze:

    Were you able to find out anything about blood donation and high altitude? I have not been able to find out anything definitive. I'm supposed to donate blood just before flying to a high altitude. I don't really want to do any re-injecting like you mentioned. Is the idea to get your red blood cell count as high as possible before going to a high altitude?

  10. Hi John,

    Sorry for the delay. I haven't looked into blood donation. In theory increasing RBC before going to altitude would help, although I don't think it would alleviate all symptoms associated with AMS. Certainly, donating blood just before may harm performance.

  11. Prior to a trek to the Khumbu region in Nepal I worked out a training regimen that seemed to help. I would go out and hike the local hills here in Santa Barbara (2000 to 3000 elevation gain)as fast as I could to try to simulate the out of breath feeling of high altitude hiking.

    This helped me in two ways. First, my body seemed to adjust to the hyperventilating to some extent. Second, it trained me to continue hiking even when out of breath. At altitude people have a tendency to stop to catch their breath. At a certain altitude it seems that it can take 10 to 15 minutes to catch one's breath and then another 10 to 15 minutes to get back in the groove. Higher up (17,000+ feet), I find that I was never able catch my breath in a reasonable time period.

    By stopping to catch your breath, when it really doesn't work, you are just prolonging your exposure to high altitude and further tiring yourself. You might as well just push on. I am of course no saying that you should push on if you are experiencing AMS.

    I've also tried Diamox on Mount Whitney - seemed to help a little. And tried Viagra on Langley - seemed to help a lot if you don't mind the blue tint to everything. In Nepal milk tea seemed to help. As a diuretic, I believe it seems to speed up the movement of water through and out of the system which may help with swelling. Not sure though.

  12. Really great info Anthony! Interesting that you found that there was some adjustment to hyperventilating.

    Good point about stopping all the time making it worse (more exposure). There's some balance - I know going very fast isn't' good for me, but so is going too slow. Nice and steady worked well for me going up Tyndall.