Altitude and the Body

During our trek through the Annapurnas we became very familiar with the effects of altitude on the body, what actually happens with our bodies is really remarkable. Most of this information comes from some doctors who were doing altitude research between Manang (3500m) and the Pass (5500m). We attended a lecture they presented in Manang and also had a long chat with them at a guest house in Throng Phedi (4400m) the evening before we did the pass.

As we climb higher in altitude the amount of oxygen available to us is less and less the higher we go. In Manang (3500m) there is about 67% of the oxygen available, compared to what we would find at sea level, on the pass (5500m) there was only 50% of the oxygen available. If you are curious, as i was, about how much less would be at the top of Everest (8800m) the doctors told us that there is only about 30% of the oxygen available at this altitude, amazing when you consider some people climb Everest without oxygen.

So, there is less oxygen at altitude, but our body still needs to function and the majority of us will be able to function in these reduced oxygen environments, if we allow our bodies to acclimitize to the altitude. When our bodies acclimitize to altitude our physiology changes quite dramatically. Once we go over the altitude of 2500m, some people will begin to feel the effects of altitude. Negative effects of altitude on the body are usually some form of AMS (Accute Mountain Sickness). If AMS is not treated properly it can worsen into a potentially fatal problem involving the pooling of blood in areas of the body where it shouldn't, such as the brain or lungs. This is referred to as HACE (High Altitude Cerebral Edema) or HAPE (High Altitude Pulminary Edema). Most of the altitude related deaths in the Annapurna region are from Nepalis, who know surprisingly little about the medical effects of altitude and correct treatments for it.

One example of where problems often arise for the Nepalise people is when they leave their home at a high altitude and visit a low atltitude for 2 or more weeks and then rush back to their homes without any proper acclimitisation. Most people on earth will be able to acclimitize up to about 5500m (above this altitude the body cannot fully acclimitize properly). Full acclimatization to altitude takes about 6 weeks, but the body can acclimatize to a functionable level much quicker than this. The correct regimen of acclimatization involves gaining 400-600 per night, no more than this. The rule of thumb is climb high, sleep low, so each day we would arrive at our guest house for the night, then would drop our bags and then climb up another few hundred meters. This helps the body acclimatize quicker.

Another, somewhat controversial way, of acclimatizing quicker is to use a drug called Diamox. This is a diaretic drug that speeds up the time that it takes the body to acclimatize. What would normally take 24-48 hours to acclimatize to, can be achieved in 3-4 hours using Diamox. The drug is often used as a treatment for AMS, but can also be used in lower doses as a preventative drug. When used in low preventative doses Diamox also helps significatly with the bodies ability to sleep properly (not being able to have a proper nights sleep is one of the more common effects of high altitude, you often wake up trying to get a good breath of air). Diamox is a diaretic though, so taking it too close to the time you go to sleep is not a good idea because you will be up all night going pee.

Right, you are probably wondering why a diaretic drug would help with altitude. If you remember the mountaneers mantra from the main article on our Annapurna trek you might remember the 'pee lots' part. The reason for this is that the body is making the blood more acidic at high altitude, this acidifying of the blood causes a reaction in the body that includes the heart pumping faster, the widening of the arteries and lungs working harder, all to more effectively deliver oxygen to to body.

When the body doesn't adapt correctly, usually from gaining too much altitude too quickly, symptoms of AMS may develop. These symptoms include dizziness, headache, vomiting and a difficulty in sleeping. More severe cases may develop into HAPE or HACE. In any of these cases the most important thing is to descend, descend, descend. Sometimes even loosing just a little bit of altitude can relieve the symptoms. We were told that about two thirds of people crossing the pass we crossed will have some symptoms of AMS, most common is a headache. Stefanie and i were okay, but we did take some small preventative doses of Diamox, plus we had done all the proper acclimatisation walks and techniques. I was a bit concerned, because the day before the pass i experienced an hour or so of destabilizing dizziness, not good, especially since we were walking on loose shale in a landslide area with serious consequences if i would have fallen. So, under the advice of the altitude doctor we both took small doses of Diamox, and it was fine.

One of the more interesting facts about acclimatization is to do with the Sherpa people of Nepal who live mainly in the Everest region. These people are the only people on earth who are known to have perfect acclimatization, they do not loose their high altitude acclimatization as they drop down to lower altitudes. These people have basically evolved this way.

As one final clarifying note with regards to acclimatization stops; you may have noticed that normal increments for acclimatizing are 400-600 meters, yet on the day of the pass we climbed a 1000 Meters. The reason for this is to do with where you are sleeping. It is possible to have massive altitude gain in a single day, as long as you don't hang about, you basically return to a lower altitude again.