High altitude and hypoxia
The air above us exerts a certain level of atmospheric pressure on every surface it contacts. As we rise in altitude, the amount of air bearing down on us decreases, and with it, atmospheric pressure also decreases, as does the pressure exerted by each of the gases in the air itself. Among these gases is oxygen. At the summit of Mont Blanc – 4,807 m.a.s.l, the partial pressure of oxygen is little more than half that found at sea level. Above 8,000 m.a.s.l, one enters the so-called “death zone” where the partial pressure of oxygen is so low that it would be impossible to survive for more than a few hours. The lower the oxygen pressure in the air, in fact, the more difficult it will be to pass into the blood from the lungs. Poor oxygenation of the blood results in poor oxygenation of other tissues, a condition known as hypoxia.