Altitude sickness (or altitude illness) is a disorder caused by being at high altitude. It commonly occurs above 8,000 feet. The cause of altitude illness is a matter of oxygen pressure. At 12,000 feet there are roughly 40% fewer oxygen molecules per breath. In order to oxygenate the body effectively, breathing rate must increase. This extra ventilation increases the oxygen content in the blood, but not to sea level concentrations. Since the amount of oxygen required for activity is the same, the body must adjust to having less oxygen. In addition, high altitude and lower air pressure cause fluid to leak from the capillaries which can cause fluid build-up in both the lungs and the brain. Continuing to higher altitudes without proper acclimatization can lead to potentially serious, even life-threatening illnesses.
The main cause of altitude sickness is going too high too fast. Given time, the body can adapt to the decrease in oxygen concentration at a specific altitude, process known as acclimatization. To acclimatize, a number of changes take place in the body occur to allow it to operate with decreased oxygen: the depth of respiration increases; the pressure in the pulmonary arteries increases forcing blood into portions of the lung which are normally not used at sea level; more red blood cells are made; more 2,4-DPG is made which facilitates the release of oxygen from hemoglobin to the body tissues. Acclimatization generally takes 1 to 3 days at a given altitude. Altitude is defined on the following scale:
- High altitude: 8,000 – 12,000 feet (2,438 – 3,658 meters);
- Very high altitude: 12,000 – 18,000 feet (3,658 – 5,487 meters); and
- Extremely high altitude: 18,000+ feet (5,500+ meters).
Most people can go up to 8,000 feet (2,438 meters) with minimal effects. If you have been at that altitude before and had no problems, you can probably return to that altitude without problems if (and only if) you are properly acclimatized. If you have not been to high altitude before, caution is strongly recommended. No specific factors such as age, sex, or physical condition are known to correlate with the susceptibility to altitude sickness. Some people are simply more susceptible than others. There is no telling, so caution is the better part of wisdom.