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Very high altitude = 3,500–5,500 metres (11,500–18,000 ft) Extreme altitude = above 5,500 metres (18,000 ft) Travel to each of these altitude regions can lead to medical problems, from the mild symptoms of acute mountain sickness to the potentially fatal high-altitude pulmonary edema and high-altitude cerebral edema .
Atmospheric pressure decreases with altitude while the O 2 fraction remains constant to about 85 km (53 mi), so PO 2 decreases with altitude as well. It is about half of its sea level value at 5,500 m (18,000 ft), the altitude of the Mount Everest base camp, and less than a third at 8,849 m (29,032 ft), the summit of Mount Everest. [8]
At 3,400 metres (11,200 ft) (67 kPa or 0.66 atm), raising the oxygen concentration level by 5% via an oxygen concentrator and an existing ventilation system provides an effective altitude of 3,000 m (10,000 ft) (70 kPa or 0.69 atm), which is more tolerable for those unaccustomed to high altitudes.
At very high altitude, from 3,500 to 5,500 metres (11,500 to 18,000 ft) arterial oxygen saturation falls below 90% and arterial P O 2 is reduced to the extent that extreme hypoxemia may occur during exercise and sleep, and if high altitude pulmonary edema occurs. In this range severe altitude illness is common. [2]
High-altitude mountaineering can induce pulmonary hypoxia due to decreased atmospheric pressure. This hypoxia causes vasoconstriction that ultimately leads to high altitude pulmonary edema (HAPE). For this reason, some climbers carry supplemental oxygen to prevent hypoxia, edema, and HAPE.
The external partial pressure of oxygen decreases with altitude, for example in areas of high altitude or when flying. This decrease results in decreased carriage of oxygen by hemoglobin. [ 13 ] This is particularly seen as a cause of cerebral hypoxia and mountain sickness in climbers of Mount Everest and other peaks of extreme altitude.
Mountain sickness may progress to HACE (high-altitude cerebral edema) and HAPE (high-altitude pulmonary edema), both of which can be fatal within 24 hours. [43] [45] [47] In high mountains, atmospheric pressure is lower and this means that less oxygen is available to breathe. [43] This is the underlying cause of altitude sickness.
Oxygen consumption is reduced to a maximum of 1 liter per minute. [8] Travelers acclimatized to high altitudes exhibit high levels of HVR, as it provides advantages such as increased oxygen intake, enhanced physical and mental performance, and lower susceptibility to illnesses associated with high altitude. [1]