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Effects of high altitude on humans
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Effects of high altitude on humans
The effects of high altitude on humans are mostly the consequences of reduced partial pressure of oxygen in the atmosphere. The medical problems that are direct consequence of high altitude are caused by the low inspired partial pressure of oxygen, which is caused by the reduced atmospheric pressure, and the constant gas fraction of oxygen in atmospheric air over the range in which humans can survive. The other major effect of altitude is due to lower ambient temperature.
The oxygen saturation of hemoglobin determines the content of oxygen in blood. After the human body reaches around 2,100 metres (6,900 ft) 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. At extreme altitudes, the ambient pressure can drop below the vapor pressure of water at body temperature, but at such altitudes even pure oxygen at ambient pressure cannot support human life, and a pressure suit is necessary. A rapid depressurisation to the low pressures of high altitudes can trigger altitude decompression sickness.
The physiological responses to high altitude include hyperventilation, polycythemia, increased capillary density in muscle and hypoxic pulmonary vasoconstriction–increased intracellular oxidative enzymes. There are a range of responses to hypoxia at the cellular level, shown by discovery of hypoxia-inducible factors (HIFs), which determine the general responses of the body to oxygen deprivation. Physiological functions at high altitude are not normal and evidence also shows impairment of neuropsychological function, which has been implicated in mountaineering and aviation accidents. Methods of mitigating the effects of the high altitude environment include oxygen enrichment of breathing air and/or an increase of pressure in an enclosed environment. Other effects of high altitude include frostbite, hypothermia, sunburn, and dehydration.
Tibetans, Andeans, and Amharas are three groups which are relatively well adapted to high altitude, but display noticeably different phenotypes.
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 kilopascals (158.53 mmHg). In healthy individuals, this saturates hemoglobin, the oxygen-binding red pigment in red blood cells.
Atmospheric pressure decreases following the Barometric formula with altitude while the O2 fraction remains constant to about 100 km (62 mi), so pO2 decreases 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.
The International Society for Mountain Medicine recognizes three altitude regions which reflect the lowered amount of oxygen in the atmosphere:
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 5,500 m (18,045 ft).
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Effects of high altitude on humans
The effects of high altitude on humans are mostly the consequences of reduced partial pressure of oxygen in the atmosphere. The medical problems that are direct consequence of high altitude are caused by the low inspired partial pressure of oxygen, which is caused by the reduced atmospheric pressure, and the constant gas fraction of oxygen in atmospheric air over the range in which humans can survive. The other major effect of altitude is due to lower ambient temperature.
The oxygen saturation of hemoglobin determines the content of oxygen in blood. After the human body reaches around 2,100 metres (6,900 ft) 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. At extreme altitudes, the ambient pressure can drop below the vapor pressure of water at body temperature, but at such altitudes even pure oxygen at ambient pressure cannot support human life, and a pressure suit is necessary. A rapid depressurisation to the low pressures of high altitudes can trigger altitude decompression sickness.
The physiological responses to high altitude include hyperventilation, polycythemia, increased capillary density in muscle and hypoxic pulmonary vasoconstriction–increased intracellular oxidative enzymes. There are a range of responses to hypoxia at the cellular level, shown by discovery of hypoxia-inducible factors (HIFs), which determine the general responses of the body to oxygen deprivation. Physiological functions at high altitude are not normal and evidence also shows impairment of neuropsychological function, which has been implicated in mountaineering and aviation accidents. Methods of mitigating the effects of the high altitude environment include oxygen enrichment of breathing air and/or an increase of pressure in an enclosed environment. Other effects of high altitude include frostbite, hypothermia, sunburn, and dehydration.
Tibetans, Andeans, and Amharas are three groups which are relatively well adapted to high altitude, but display noticeably different phenotypes.
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 kilopascals (158.53 mmHg). In healthy individuals, this saturates hemoglobin, the oxygen-binding red pigment in red blood cells.
Atmospheric pressure decreases following the Barometric formula with altitude while the O2 fraction remains constant to about 100 km (62 mi), so pO2 decreases 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.
The International Society for Mountain Medicine recognizes three altitude regions which reflect the lowered amount of oxygen in the atmosphere:
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 5,500 m (18,045 ft).
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