Mountaineering
The effects of altitude

Altitude can effect different people in different ways. Some people are more prone to altitude sickness than others. Some people can perform well on one expedition and then on their next trip into the mountains it's a completely different story. The following explains the effects of altitude on the body.

Altitude sickness

Altitude sickness, also known as acute mountain sickness (AMS) or altitude illness is a pathological condition that is caused by acute exposure to high altitudes. It commonly occurs above 2,400 metres (approximately 8,000 feet). Acute mountain sickness can progress to high altitude pulmonary edema (HAPE) or high altitude cerebral edema (HACE).

Altitude sickness does not typically manifest in persons traveling in aircraft, as the cabins of modern flights are generally pressurized.

Another rarer type of altitude sickness caused by prolonged exposure to high altitude is chronic mountain sickness, also known as Monge's disease.

Different people have different susceptibilities to altitude sickness. For some otherwise healthy people Acute mountain sickness (AMS) can begin to appear at around 2000 meters (6,500 feet) above sea level such as at many mountain ski resorts. AMS is the most frequent type of altitude sickness encountered. Symptoms often manifest themselves 6 to 10 hours after ascent and generally subside in 1 to 2 days, but they occasionally develop into the more serious conditions. Symptoms are described as headache with fatigue, stomach sickness, dizziness, and sleep disturbance as additional possible symptoms. Exertion aggravates the symptoms.

High altitude pulmonary edema (HAPE)

High altitude pulmonary edema (HAPE) is a life threatening form of non-cardiogenic pulmonary edema that occurs in otherwise healthy mountaineers at altitudes above 2500m. Some cases have however been reported also at lower altitudes (between 1500 and 2500m in highly vulnerable subjects), although what makes some people susceptible to HAPE is not currently known. HAPE remains the major cause of death related to high altitude exposure with a high mortality in absence of emergency treatment.

The initial insult that causes HAPE is a shortage of oxygen which is caused by the lower air pressure at high altitudes.[1] The mechanisms by which this shortage of oxygen causes HAPE are poorly understood, but two processes are believed to be important:

Although higher pulmonary arterial pressures are associated with the development of HAPE, the presence of pulmonary hypertension may not in itself be sufficient to explain the development of edema: severe pulmonary hypertension can exist in the absence of clinical HAPE in subjects at high altitude.

Individual susceptibility to HAPE is difficult to predict. The most reliable risk factor is previous susceptibility to HAPE, and there is likely to be a genetic basis to this condition, perhaps involving the gene for angiotensin converting enzyme (ACE).

High altitude cerebral edema (or HACE)

High altitude cerebral edema (or HACE) is a severe (frequently fatal) form of altitude sickness. HACE is the result of swelling of brain tissue from fluid leakage. Symptoms can include headache, loss of coordination (ataxia), weakness, and decreasing levels of consciousness including disorientation, loss of memory, hallucinations, psychotic behavior, and coma. It generally occurs after a week or more at high altitude. Severe instances can lead to death if not treated quickly. Immediate descent is a necessary life-saving measure (2,000 - 4,000 feet). There are some medications (e.g. dexamethasone) that may be prescribed for treatment in the field, but these require proper medical training in their use. Anyone suffering from HACE must be evacuated to a medical facility for proper follow-up treatment. A Gamow bag can sometimes be used to stabilize the sufferer before transport or descending.

Climbers may also suffer high altitude pulmonary edema (HAPE), which affects the lungs. While not nearly as life threatening as HACE in the initial stages, failure to descend to lower altitudes or receive medical treatment can also lead to death. High altitude peripheral edema is less common, but thought by some to be underdiagnosed, often being mistaken for trench foot.

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