Into thin air: Medical problems at new heights
It used to be a problem for the very few, the hardy adventurers who trek or climb at breathtaking heights. But high places continue to beckon, and as travel becomes easier and less expensive, more and more men are responding with their ascent. If you maintain a low profile, you don't have to worry about altitude sickness, but if your travel plans are uplifting, you should know how to handle new heights.
Although a low oxygen level is the most obvious and important cause of altitude sickness, several factors actually combine to trigger problems:
Oxygen. Oxygen levels are highest at sea level, but they fall steadily at increasing altitudes. Most men won't notice any effect until about 5,000 feet; even at one mile above sea level, breathing is comfortable at rest but becomes labored with exertion. And the higher you go, the harder your lungs have to work to take in the oxygen you need.