Altitude sickness—also known as acute mountain sickness (AMS), altitude illness, hypobaropathy, the altitude bends, or soroche—is a pathological effect of high altitude on humans, caused by acute exposure to low partial pressure of oxygen at high altitude. It commonly occurs above 2,400 metres (8,000 feet). It presents as a collection of nonspecific symptoms, acquired at high altitude or in low air pressure, resembling a case of flu, carbon monoxide poisoning, or a hangover It is hard to determine who will be affected by altitude sickness, as there are no specific factors that correlate with a susceptibility to altitude sickness. However, most people can ascend to 2,400 metres (8,000 ft) without difficulty. Acute mountain sickness can progress to high altitude pulmonary edema (HAPE) or high altitude cerebral edema (HACE), which are potentially fatal. Chronic mountain sickness, also known as Monges disease, is a different condition that only occurs after very prolonged exposure to high altitude. CAUSES: The available amount of oxygen to sustain mental and physical alertness decreases with altitude. Available oxygen drops as the air density itself, the number of molecules (of both oxygen and nitrogen) per given volume, drops as altitude increases. However, the percentage of oxygen in air, at 21%, remains almost unchanged up to 21,000 meters (69,000 ft).The RMS velocities of diatomic nitrogen and oxygen are very similar and thus no change occurs in the ratio of oxygen to nitrogen. Dehydration due to the higher rate of water vapor lost from the lungs at higher altitudes may contribute to the symptoms of altitude sickness.[7] The rate of ascent, altitude attained, amount of physical activity at high altitude, as well as individual susceptibility, are contributing factors to the onset and severity of high-altitude illness. Altitude sickness usually occurs following a rapid ascent and can usually be prevented by ascending slowly.In most of these cases, the symptoms are temporary and usually abate as altitude acclimatization occurs. However, in extreme cases, altitude sickness can be fatal. Signs and symptoms. People have different susceptibilities to altitude sickness; for some otherwise healthy people, acute altitude sickness can begin to appear at around 2000 meters (6,500 ft) above sea level, such as at many mountain ski resorts, equivalent to a pressure of 80 kPa.This is the most frequent type of altitude sickness encountered. Symptoms often manifest themselves six to ten hours after ascent and generally subside in one to two days, but they occasionally develop into the more serious conditions. Symptoms include headache, fatigue, stomach illness, dizziness, and sleep disturbance.Exertion aggravates the symptoms. The Lake Louise assessment system of AMS is based on a self-report questionnaire as well as a quick clinical assessment. Those individuals with the lowest initial partial pressure of end-tidal pCO2 (the lowest concentration of carbon dioxide at the end of the respiratory cycle, a measure of a higher alveolar ventilation) and corresponding high oxygen saturation levels tend to have a lower incidence of acute mountain sickness than those with high end-tidal pCO2 and low oxygen saturation levels. Primary symptoms. Headaches are the primary symptom used to diagnose altitude sickness, although a headache is also a symptom of dehydration. A headache occurring at an altitude above 2,400 metres (8,000 feet = 76 kPa), combined with any one or more of the following symptoms, may indicate altitude sickness: Lack of appetite, nausea, or vomiting Fatigue or weakness Dizziness or lightheadedness Insomnia Pins and needles Shortness of breath upon exertion Nosebleed Persistent rapid pulse Drowsiness Excessive flatulation[8] General malaise Peripheral edema (swelling of hands, feet, and face) Severe symptoms. Symptoms that may indicate life-threatening altitude sickness include: Pulmonary edema (fluid in the lungs) Symptoms similar to bronchitis Persistent dry cough Fever Shortness of breath even when resting Cerebral edema (swelling of the brain) Headache that does not respond to analgesics Unsteady gait Gradual loss of consciousness Increased nausea Retinal hemorrhage The most serious symptoms of altitude sickness arise from edema (fluid accumulation in the tissues of the body). At very high altitude, humans can get either high altitude pulmonary edema (HAPE), or high altitude cerebral edema (HACE). The physiological cause of altitude-induced edema is not conclusively established. It is currently believed, however, that HACE is caused by local vasodilation of cerebral blood vessels in response to hypoxia, resulting in greater blood flow and, consequently, greater capillary pressures. On the other hand, HAPE may be due to general vasoconstriction in the pulmonary circulation (normally a response to regional ventilation-perfusion mismatches) which, with constant or increased cardiac output, also leads to increases in capillary pressures. For those suffering HACE, dexamethasone may provide temporary relief from symptoms in order to keep descending under their own power. HAPE can progress rapidly and is often fatal. Symptoms include fatigue, severe dyspnea at rest, and cough that is initially dry but may progress to produce pink, frothy sputum. Descent to lower altitudes alleviates the symptoms of HAPE. HACE is a life-threatening condition that can lead to coma or death. Symptoms include headache, fatigue, visual impairment, bladder dysfunction, bowel dysfunction, loss of coordination, paralysis on one side of the body, and confusion. Descent to lower altitudes may save those afflicted with HACE.
Posted on: Sat, 17 Jan 2015 06:42:53 +0000
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