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High-altitude adaptation in humans

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 extremely high altitudes. This adaptation means irreversible, long-term physiological responses to high-altitude environments, associated with heritable behavioural and genetic changes. While the rest of the human population would suffer serious health consequences, the indigenous inhabitants of these regions thrive well in the highest parts of the world. ...

High-altitude cerebral edema

High-altitude cerebral edema is a medical condition in which the brain swells with fluid because of the physiological effects of traveling to a high altitude. It generally appears in patients who have acute mountain sickness and involves disorientation, lethargy, and nausea among other symptoms. It occurs when the body fails to acclimatize while ascending to a high altitude. It appears to be a vasogenic edema fluid penetration of the blood–brain barrier, although cytotoxic edema cellular retention of fluids may play a role as well. Individuals with the condition must immediately descend to ...

High-altitude flatus expulsion

High-altitude flatus expulsion is a gastrointestinal syndrome which involves the spontaneous passage of increased quantities of rectal gases at high altitudes. First described by Joseph Hamel in c. 1820 and occasionally described afterward, a landmark study of this phenomenon was published in 1981 by Paul Auerbach and York Miller. The phenomenon is based on the differential in atmospheric pressure, directly correlated with the observers frequency of and level of experience in high-altitude metabolism. As the external pressure decreases, the difference in pressure between the gas within the ...

High-altitude pulmonary edema

High-altitude pulmonary edema is a life-threatening form of non-cardiogenic pulmonary edema that occurs in otherwise healthy people at altitudes typically above 2.500 meters. However, cases have also been reported between 1.500–2.500 metres or 4.900–8.200 feet in more vulnerable subjects. Classically, HAPE occurs in persons normally living at low altitude who travel to an altitude above 2.500 meters 8.200 feet. Re-entry HAPE is also an entity that has been described in persons who normally live at high altitude but who develop pulmonary edema after returning from a stay at low altitude. Th ...

Hunting reaction

The hunting reaction or hunting response is a process of alternating vasoconstriction and vasodilation in extremities exposed to cold. The term Lewis reaction is used too, named after Thomas Lewis, who first described the effect in 1930. Vasoconstriction occurs first to reduce heat loss, but also results in strong cooling of the extremities. Approximately five to ten minutes after the start of cold exposure, the blood vessels in the extremities will suddenly vasodilate. This is probably caused by a sudden decrease in the release of neurotransmitters from the sympathetic nerves to the muscu ...

Hypoxia (medical)

Hypoxia is a condition in which the body or a region of the body is deprived of adequate oxygen supply at the tissue level. Hypoxia may be classified as either generalized, affecting the whole body, or local, affecting a region of the body. Although hypoxia is often a pathological condition, variations in arterial oxygen concentrations can be part of the normal physiology, for example, during hypoventilation training or strenuous physical exercise. Hypoxia differs from hypoxemia and anoxemia in that hypoxia refers to a state in which oxygen supply is insufficient, whereas hypoxemia and ano ...

Photokeratitis

Photokeratitis or ultraviolet keratitis is a painful eye condition caused by exposure of insufficiently protected eyes to the ultraviolet rays from either natural or artificial sources. Photokeratitis is akin to a sunburn of the cornea and conjunctiva, and is not usually noticed until several hours after exposure. Symptoms include increased tears and a feeling of pain, likened to having sand in the eyes. The injury may be prevented by wearing eye protection that blocks most of the ultraviolet radiation, such as welding goggles with the proper filters, a welders helmet, sunglasses rated for ...

Portable hyperbaric bag

A portable hyperbaric bag, of which one brand is the Gamow bag, is an inflatable pressure bag large enough to accommodate a person inside. A person can be placed inside the bag which is sealed and inflated with a foot pump. Within minutes, the effective altitude can be decreased by 1000 to as much as 3000 meters depending on the elevation. The bag is pressurised to 105-220 mmHg, pressure gradient is regulated by pop-off valves set to the target pressure. It is primarily used for treating severe cases of altitude sickness, high-altitude cerebral edema, and high-altitude pulmonary edema. Lik ...