[1][2] Research at high altitude is also an important way to learn about sea level conditions that are caused or complicated by hypoxia such as chronic lung disease and sepsis.
Patients with these conditions are very complex and usually suffer from several other diseases at the same time, so it is virtually impossible to work out which of their problems is caused by lack of oxygen.
Altitude research gets round this by studying the effects of oxygen deprivation on otherwise healthy people.
Although the shortage of air contributes to the effects on the human body, research has found that most altitude sicknesses can be linked to the lack of atmospheric pressure.
At 26,000 feet the body reaches a maximum and can no longer adjust to the altitude, often referred to as the "Death Zone".