Physiology of High Altitude Flying 1942 US Army Air Corps Pilot Training Film TF1-313; World War II

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Originally a public domain film from the US Army Air Forces, slightly cropped to remove uneven edges, with the aspect ratio corrected, and one-pass brightness-contrast-color correction & mild video noise reduction applied.

The soundtrack was also processed with volume normalization, noise reduction, clipping reduction, and/or equalization (the resulting sound, though not perfect, is far less noisy than the original).

https://en.wikipedia.org/wiki/Effects_of_high_altitude_on_humans

Wikipedia license: http://creativecommons.org/licenses/by-sa/3.0/

The effects of high altitude on humans are considerable. The percentage oxygen saturation of hemoglobin determines the content of oxygen in blood. After the human body reaches around 2,100 m (7,000 feet) above sea level, the saturation of oxyhemoglobin begins to decrease rapidly. However, the human body has both short-term and long-term adaptations to altitude that allow it to partially compensate for the lack of oxygen. There is a limit to the level of adaptation; mountaineers refer to the altitudes above 8,000 metres (26,000 ft) as the death zone, where it is generally believed that no human body can acclimatize...

Effects as a function of altitude

The human body can perform best at sea level, where the atmospheric pressure is 101,325 Pa or 1013.25 millibars (or 1 atm, by definition). The concentration of oxygen (O2) in sea-level air is 20.9%, so the partial pressure of O2 (pO2) is 21.136 kPa. In healthy individuals, this saturates hemoglobin, the oxygen-binding red pigment in red blood cells.

Atmospheric pressure decreases exponentially with altitude while the O2 fraction remains constant to about 100 km, so pO2 decreases exponentially with altitude as well. It is about half of its sea-level value at 5,000 m (16,000 ft), the altitude of the Everest Base Camp, and only a third at 8,848 m (29,029 ft), the summit of Mount Everest. When pO2 drops, the body responds with altitude acclimatization.

Mountain medicine recognizes three altitude regions which reflect the lowered amount of oxygen in the atmosphere:

High altitude = 1,500–3,500 metres (4,900–11,500 ft)

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 (HAPE) and high-altitude cerebral edema (HACE). The higher the altitude, the greater the risk. Expedition doctors commonly stock a supply of dexamethasone, to treat these conditions on site. Research also indicates elevated risk of permanent brain damage in people climbing to above 5500 m.

Humans have survived for two years at 5,950 m (19,520 ft, 475 millibars of atmospheric pressure), which is the highest recorded permanently tolerable altitude; the highest permanent settlement known, La Rinconada, is at 5,100 m (16,700 ft).

At altitudes above 7,500 m (24,600 ft, 383 millibars of atmospheric pressure), sleeping becomes very difficult, digesting food is near-impossible, and the risk of HAPE or HACE increases greatly...