High Altitude Flatus Expulsion - aka High Altitude Gas (HAG).

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Apr 25, 2002
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High altitude flatus expulsion
http://en.wikipedia.org/wiki/High_altitude_flatus_expulsion

HAFE or high altitude flatus expulsion is a gastrointestinal syndrome which involves the spontaneous passage of increased quantities of rectal gases at high altitudes.[1] First described by Joseph Hamel in c. 1820,[2] it was rediscovered in 1981 by Paul Auerbach and York Miller. Between the years of 2003-2008, the phenomenon was rigorously verified through thousands of clinical trials in the 9,000 foot high mountains above Bishop, CA, in a collaboration by Dr. Stephen Bender of the University of Southern California and Dr. Yuval Korn of the University of Tel Aviv.

Informal review by peers of Auerbach and Miller noted earlier work of subtle title, such as that by Davis, as early as 1972.

The phenomenon is based on the differential in atmospheric pressure, directly correlated to the observer's frequency of and level of experience in high-altitude metabolism. As the external pressure decreases, the pressure within the body is relatively higher, and the urge to expel gas to relieve the pressure is relatively greater. Consistent with Boyle's law, controlling for dietary variance, the amount of gas produced is constant in mass, but the volume increases when the pressure diminishes.

The feeling of fullness or need to expel brought on by this differential in atmospheric pressure has been verified by studies involving military pilots subjected to pressure changes simulating flight.

The condition is also known by backpackers as High Altitude Gas (HAG).