The Causes of Altitude Sickness
The percentage of oxygen in the atmosphere at sea level is about 21% and the barometric pressure is around 760 mm Hg. As altitude increases, the percentage remains the same but the number of oxygen molecules per breath is reduced. At 3,600 meters (12,000 feet) the barometric pressure is only about 480 mm Hg, so there are roughly 40% fewer oxygen molecules per breath so the body must adjust to having less oxygen.
In addition, high altitude and lower air pressure causes fluid to leak from the capillaries in both the lungs and the brain which can lead to fluid build-up. Continuing on to higher altitude without proper acclimatization can lead to the potentially serious, even life-threatening altitude sickness.
The main cause of altitude sickness is going too high too quickly. Given enough time, your body will adapt to the decrease in oxygen at a specific altitude. This process is known as acclimatization and generally takes one to three days at any given altitude, e.g. if you climb to 3,000 meters and spend several days at that altitude, your body will acclimatize to 3,000 meters. If you then climb to 5,000 meters your body has to acclimatize once again.
Several changes take place in the body which enable it to cope with decreased oxygen
The depth of respiration increases.
The body produces more red blood cells to carry oxygen.
Pressure in pulmonary capillaries is increased, "forcing" blood into parts of the lung which are not normally used when breathing at sea level.
The body produces more of a particular enzyme that causes the release of oxygen from hemoglobin to the body tissues.
Above 3,000 meters (10,000 feet) most people experience a periodic breathing during sleep known as Cheyne-Stokes Respirations. The pattern begins with a few shallow breaths and increases to deep sighing respirations then falls off rapidly even ceasing entirely for a few seconds and then the shallow breaths begin again. During the period when breathing stops the person often becomes restless and may wake with a sudden feeling of suffocation. This can disturb sleeping patterns, exhausting the climber. This type of breathing is not considered abnormal at high altitudes. Acetazolamide is helpful in relieving this periodic breathing.
Acute Mountain Sickness (AMS)
AMS is very common at high altitude. At over 3,000 meters (10,000 feet) 75% of people will have mild symptoms. The occurrence of AMS is dependent upon the elevation, the rate of ascent, and individual susceptibility. Many people will experience mild AMS during the acclimatization process. The symptoms usually start 12 to 24 hours after arrival at altitude and begin to decrease in severity around the third day.
The symptoms of Mild AMS include:
Nausea & Dizziness
Loss of appetite
Shortness of breath
General feeling of malaise
Symptoms tend to be worse at night and when respiratory drive is decreased. Mild AMS does not interfere with normal activity and symptoms generally subside within two to four days as the body acclimatises. As long as symptoms are mild, and only a nuisance, ascent can continue at a moderate rate. When hiking, it is essential that you communicate any symptoms of illness immediately to others on your trip.
The signs and symptoms of Moderate AMS include
Severe headache that is not relieved by medication
Nausea and vomiting, increasing weakness and fatigue
Shortness of breath
Decreased coordination (ataxia).
Normal activity is difficult, although the person may still be able to walk on their own. At this stage, only advanced medications or descent can reverse the problem. Descending only 300 meters (1,000 feet) will result in some improvement, and twenty four hours at the lower altitude will result in a significant improvement. The person should remain at lower altitude until all the symptoms have subsided (up to 3 days). At this point, the person has become acclimatized to that altitude and can begin ascending again.
The best test for moderate AMS is to have the person walk a straight line heel to toe just like a sobriety test. A person with ataxia would be unable to walk a straight line. This is a clear indication that an immediate descent is required. It is important to get the person to descend before the ataxia reaches the point where they cannot walk on their own (which would necessitate a stretcher evacuation).
Severe AMS results in an increase in the severity of the aforementioned symptoms including: Ÿ Shortness of breath at rest, Ÿ Inability to walk, Ÿ Decreasing mental status, Ÿ Fluid build-up in the lungs, Severe AMS requires an immediate descent of around 600 meters (2,000 feet) to a lower altitude.
There are two serious conditions associated with severe altitude sickness; High Altitude Cerebral Oedema (HACO) and High Altitude Pulmonary Oedema (HAPO). Both of these happen less frequently, especially to those who are properly acclimatized. But, when they do occur, it is usually in people going too high too fast or going very high and staying there. In both cases the lack of oxygen results in leakage of fluid through the capillary walls into either the lungs or the brain.
High Altitude Pulmonary Oedema (HAPO)
HAPO results from fluid build up in the lungs. This fluid prevents effective oxygen exchange. As the condition becomes more severe, the level of oxygen in the bloodstream decreases, which leads to cyanosis, impaired cerebral function, and death.
Symptoms of HAPO include
Shortness of breath at rest
Tightness in the chest, and a persistent cough bringing up white, watery, or frothy fluid
Marked fatigue and weakness
A feeling of impending suffocation at night
Confusion, and irrational behavior
Confusion, and irrational behavior are signs that insufficient oxygen is reaching the brain. One of the methods for testing yourself for HAPO is to check your recovery time after exertion.
In cases of HAPO, immediate descent of around 600 meters (2,000 feet) is a necessary life-saving measure. Anyone suffering from HAPO must also be evacuated to a medical facility for proper follow-up treatment.
Have you, or someone you know, ever suffered from HAPO or HAPE (high altitude pulmonary oedema/edema)? Then join the "International HAPE Database" a registry of previous HAPE sufferers worldwide who might consider participating in future research studies.
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Medical way to prevent Acute Mountain Sickness
Medicines are necessary and important to people when we reach higher places. There are some medicines for prevention, and some for treatment.
Anyhow, there are some medicines that have been already confirmed to be helpful to prevent Acute Mountain Sickness such as Diamox, acetazolamide, dexamethasone, and nifedipine. But we have to ask the doctors what kind of medicines we could have. Please do not buy it by yourselves, for example, people who are allergic to sulfa drugs should not take Diamox.
They should try other Medicines.