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The summit of K2, the second highest mountain on Earth, is in the death zone. At an altitude of 19,000 m (63,000 ft), the atmospheric pressure is sufficiently low that water boils at the normal temperature of the human body. This altitude is known as the Armstrong limit.
High-altitude adaptation in humans is an instance of evolutionary modification in certain human populations, including those of Tibet in Asia, the Andes of the Americas, and Ethiopia in Africa, who have acquired the ability to survive at altitudes above 2,500 meters (8,200 ft). [1]
Failure to acclimatize may result in altitude sickness, including high-altitude pulmonary edema or cerebral edema . [11] [12] Humans have survived for 2 years at 5,950 m (19,520 ft) [475 millibars (14.0 inHg; 6.89 psi) of atmospheric pressure], which appears to be near the limit of the permanently tolerable highest altitude. [13]
A person that stays for a period of time at higher altitudes acclimates, producing fewer effects over the human body. [3] There are several mechanisms that help with acclimation, which are an increase of pulmonary ventilation, higher erythrocytes levels, increase of the pulmonary diffusion capacity and increase of the vascularization of the ...
The Armstrong limit or Armstrong's line is a measure of altitude above which atmospheric pressure is sufficiently low that water boils at the normal temperature of the human body. Exposure to pressure below this limit results in a rapid loss of consciousness, followed by a series of changes to cardiovascular and neurological functions, and ...
The higher the altitude, the more likely are serious effects. [10] The human body can adapt to high altitude by breathing faster, having a higher heart rate, and adjusting its blood chemistry. [19] [20] It can take days or weeks to adapt to high altitude.
The adaptation of humans to high altitude is an example of natural selection in action. [2] High-altitude adaptations provide examples of convergent evolution, with adaptations occurring simultaneously on three continents. Tibetan humans and Tibetan domestic dogs share a genetic mutation in EPAS1, but it has not been seen in Andean humans. [3]
High altitude breathing apparatus is a breathing apparatus which allows a person to breathe more effectively at an altitude where the partial pressure of oxygen in the ambient atmospheric air is insufficient for the task or to sustain consciousness or human life over the long or short term.