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?





Discussion:

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.



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.




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.

Zé