Altitude, acclimatization

Johnson (2000). Increases in submaximal cycling efficiency mediated by altitude acclimatization. J. Appl. Physiol. 1189-1197. 

What causes high-altitude sickness, and what is high-altitude acclimatization ... 

Human evolution has taken place close to sea level, and humans are physiologically adjusted to the absolute partial pressure of the oxygen at that point, namely 21.2 kPa (159.2 mm Hg), ie, 20.946% of 101.325 kPa (760 mm Hg). However, humans may become acclimatized to life and work at altitudes as high as 2500—4000 m. At the 3000-m level, the atmospheric pressure drops to 70 kPa (523 mm Hg) and the oxygen partial pressure to 14.61 kPa (110 mm Hg), only slightly above the 13.73 kPa (102.9 mm Hg) for the normal oxygen pressure in alveolar air. To compensate, the individual is forced to breathe much more rapidly to increase the ratio of new air to old in the lung mixture. 

Adaptation to CO toxicity also seems to occur in humans. Doing experiments on herself, KiUick (1940) found diminished symptoms and lower COHb on chronic exposure to CO than in the beginning, which is in accord with the data of Haldane and Priestley (1935). Adaptation to hypoxia is the reason why people living at high altitudes feel perfectly normal while a visitor Irom the plains may feel quite unwell. Indian and Pakistani soldiers are facing one another in Siachen of Kashmir, the highest place for any military confrontation in the world. Unless the soldiers are acch-matized before they go to Siachen, many develop fatal pulmonary edema if they are acclimatized, the incidence of pulmonary toxicity is considerably reduced. 

A disorder occurring in individuals exposed to high altitudes (about 3048 m [10,000 ft]) for relatively long periods (24 hours or more). It presents as malaise, headache, and vomiting attributed to cerebral and pulmonary edema. It is probably related to both hypoxia and decreased atmospheric pressure. It may be prevented by proper acclimatization. Acute Radiation Syndrome... 

For some who climb high mountains, it is important to stop and acclimatize for several days at increasing altitudes. At very high altitudes, it may be necessary to use an oxygen tank. 

Opitz E. Increased vascularization of the tissue due to acclimatization to high altitude and its significance for the oxygen transport. Exp Med Surg 1951 9 389-403. 

III. Importance of Acclimatization to Long-Term Hypoxia at Altitude and Hormonal Control of Dopaminergic Metabolism in the Carotid Bodies... 

A proper acclimatization to hypoxia is very important and determines the overall ability to cope with hypoxia. In climbers at very high altitude, the maximum altitude that an individual can reach is clearly related to the hypoxic ventilatory response measured at sea level and to the extent of the ventilatory acclimatization during ascension (46,46a). At lower altitude, a proper ventilatory acclimatization is also a determinant mechanism for the overall hypoxic acclimatization. Our own observations (unpublished) in rats permanently living at 3600 m above sea level (Bolivian Institute for Altitude Biology—IBBA, La Paz, Bolivia) revealed that following surgical chemodenervation, the hematocrit rose from a baseline level of around 50% to more than 70% within a few weeks and numerous animals died during this period. 

Lahiri S, Rozanov C, Chemiack NS. Altered structure and fimction of the carotid hody at high altitude and associated chemoreflexes. High Alt Med Biol 2000 1 63-74. Bisgard GE. Carotid body mechanisms in acclimatization to hypoxia. Respir Physiol 2000 121 237-246. 

Tatsumi K, Pickett CK, Weil JV Possible role of dopamine in ventilatory acclimatization to high altitude. Respir Physiol 1995 99 63-73. 

Healthy individuals undergo adaptive responses to prolonged hypoxia when aceUmatizing to high altitude. Most recently, evidence has emerged that even short-duration exposures to very mild hypoxia, such as those eommonly associated with the reduction in cabin pressure during commercial airline flight, can induce an acclimatization response (93). Individuals with a variety of eardiorespiratory... 

The air at the elevations on the Plateau contains 35-40% less oxygen than at sea level. Pulmonary edema can occur at 3,000 m (9842.5 ft) elevation at Golmud for people who have come from near sea level. The abrupt rise to 4,000-5,000 m (13,123-16,404 ft) in a short time can even cause problems for people from Golmud, which is why the passenger trains are sealed, pressurized, and have added oxygen for the comfort of travelers. When tourists were crossing the Plateau to Lhasa by bus, they were required to travel nonstop for 24 h to minimize the risk of injury or death. Most healthy people will have altitude sickness at these elevations until they have acclimatized. 

Acclimation to high altitudes with reduced oxygen levels occurs when the body can maintain an adequate supply of oxygen to meet the metabolic demands of work. Those most sensitive to reduced barometric pressure risks are individuals who are either not sufficiently acclimatized to oxygen-deficient atmospheres or suffer from medical conditions that may be aggravated at altitude. Rapid ascents to high altitudes in unacclimated individuals can result in death. 

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