As altitude increases, the percentage of oxygen in the air remains constant, but atmospheric pressure decreases, causing the air to become thinner, so less oxygen is available.
For example, compared to the air at sea level, the air at about 5,800 m contains only half as much oxygen.
Most people can climb between 1,500 and 2,000m in a day without problems, but about 20% of people who climb up to 2,500m and 40% of those who climb to 3,000m suffer some form of altitude sickness.
The organs most frequently affected by altitude sickness are:
The brain (acute mountain sickness and, rarely, high-altitude cerebral edema)
The lungs (causing high altitude pulmonary edema)
The probability of suffering from altitude sickness varies greatly from one person to another. But in general, the risk increases with:
Suffering from previous altitude sickness
Living at sea level or at a very low altitude (below 900 meters)
Climb to high altitude too fast
Sleeping at too high an altitude
The body adapts (acclimatizes) to higher altitudes by increasing respiration and producing more red blood cells (erythrocytes) to carry oxygen to the tissues, as well as by making other adaptations.
Most people can adapt to altitudes of up to 3,000m in a few days. Adapting to higher altitudes requires many days or even weeks, but some people can, over time, carry out almost all normal activities at altitudes above 5,300 m. However, no one can fully acclimate to living permanently above that altitude.
Prevention of altitude sickness
The best way to prevent altitude sickness is to ascend slowly. The altitude at which a person sleeps is more important than the maximum altitude reached during the day.
Control of the rate of ascent (known as graded ascent) is essential for any activity above 2,500 meters. Above 3,000 meters, climbers or hikers should not increase their sleeping altitude to more than 300-500 meters a day, and should include a rest day (sleep at the same altitude) every 3-4 nights before sleeping. at higher altitudes. If they cannot limit their daily ascent to less than 500 meters, they must limit their average ascent for the entire ascent to less than 500 meters per day. The latter may require adding rest days. During rest days you can ascend to higher heights, as long as you return to the lower level to sleep.
The ability to ascend without symptoms varies from person to person. Therefore, group ascent should be done at the pace of the person who acclimatizes slowest to the high altitude.
Acclimatization is rapidly lost. If acclimatised persons have descended to lower levels for more than a few days, upon re-ascending they must again make a gradual ascent.
drugs or substances
Acetazolamide, which can be started the night before the ascent, reduces the chance of altitude sickness. If taken early in the illness, it can help reduce symptoms. Treatment with acetazolamide should be discontinued when descent begins or after a few days have passed at maximum altitude. Dexamethasone, an alternative to acetazolamide, can also reduce the chance of acute altitude sickness and treat its symptoms.
Taking pain relievers, such as nonsteroidal anti-inflammatory drugs (NSAIDs), can help prevent headaches that occur when you’re at high altitude.
People who have had previous episodes of high-altitude pulmonary edema should watch for any recurring symptoms and descend immediately if symptoms appear. As a preventative measure, some doctors also recommend that these people take the drugs nifedipine or tadalafil by mouth.