Effects of High Altitude
Katelin Anderson
Altitude increases have multiple effects on the human body, particularly at high altitudes. The definition of high altitude is not consistent, however, there are definite physical effects of altitude on the majority of individuals at altitudes above 3,000 meters or a little less than 9,850 feet (Ward 33). Many of these changes or complications are due to hypoxia, the deprivation of oxygen, but others are a function of other occurrences found at the elevations at which these altitude effects occur.
It is possible for humans to function normally at high altitudes, either through having been born and raised at altitude, as seen in populations native to high altitudes or lowlanders who have become acclimatized. However, long term exposure to high altitudes carries certain risks, most notably long term mountain sickness, related to the more immediate danger of acute mountain sickness.
Among people remaining high altitudes for long periods of time, there is a risk of chronic mountain sickness (CMS). The symptoms of CMS are rather vague, including headaches, dizziness, fatigue, difficulties in concentrating, and loss of mental focus, as well as irritability, depression, and even hallucinations (Ward 252). Low exercise tolerance is common and weight gain is a possibility. However, these symptoms disappear on return to a lower altitude.
Acute mountain sickness (AMS) occurs when an individual ascends to a high altitude too quickly. Most commonly, symptoms show several hours after arrival. Headaches, loss of appetite (anorexia), nausea, vomiting, lethargy, malaise, and disturbed sleep are the most prevalent symptoms of AMS (Ward 215). A slight fever is also sometimes present.
They are generally considered to be worst on the second and third days but disappear by day five, but may reappear if ascent continues. In this form, it is considered simple or benign AMS. However, severe forms of AMS are known as malignant AMS and are potentially fatal. These are high altitude pulmonary edema (HAPE) and high altitude cerebral edema (HACE). AMS is not related to physical fitness and can affect anyone, though strenuous exercise on the day of arrival is considered a possible risk factor, especially for HAPE. AMS can be prevented by slow ascent and drugs, mostly acetazolamide, usually 1,000 mg a day orally 48 hours prior to ascent and 48 hours after arrival (United States 19).
Though AMS has a clearly defined set of symptoms, there are varying degrees of contraction and seriousness. The Lake Louise scoring system provides a scaled scoring method to determine general severity of AMS, though the diagnosis cannot be made without added factors, such as a recent ascension in height and a period of several hours time before the symptoms presented (Ward 217). The Lake Lousie scoring system can be found here.
There are, of course, other effects of altitude beyond AMS. A loss of weight after arrival at high altitudes is common, but generally stabilizes. This weight loss has been attributed to a reduced diet (possibly connected to the anorexia present in AMS), greater water loss from hyperventilation, and a loss of stored body fat (West 37). Hypoxia in the tissues of the body also results in altered performance both mentally and physically, resulting in a lowered ability to perform tasks effectively or learn new ones, especially at increased altitudes (West 32). However, even after long term exposure to high altitudes, these effects will reverse at lower altitudes eventually, usually within two years at the most.
Sleep disturbance is also a significant concern at high altitudes. In addition to insomnia associated with AMS, there is record of frequent waking and reduced REM sleep and it is common for individuals to be unable to sleep for the first one or two nights at high altitude. More problematic is the characteristic periodic breathing that occurs during sleep at high altitudes. A study by West, et al. in 1986 showed that at 6,300 meters, or about 20,670 feet, there was about an eight second apneic period between breaths. However, these periods may be as long as 10 to 15 seconds (Ward 156).
The treatment for most of these conditions is either treatment of symptoms or removal from the increased altitude, especially in severe cases of AMS. Once an individual returns to a lower altitude, the symptoms, both physiological and mental, should eventually vanish.
It is possible for humans to function normally at high altitudes, either through having been born and raised at altitude, as seen in populations native to high altitudes or lowlanders who have become acclimatized. However, long term exposure to high altitudes carries certain risks, most notably long term mountain sickness, related to the more immediate danger of acute mountain sickness.
Among people remaining high altitudes for long periods of time, there is a risk of chronic mountain sickness (CMS). The symptoms of CMS are rather vague, including headaches, dizziness, fatigue, difficulties in concentrating, and loss of mental focus, as well as irritability, depression, and even hallucinations (Ward 252). Low exercise tolerance is common and weight gain is a possibility. However, these symptoms disappear on return to a lower altitude.
Acute mountain sickness (AMS) occurs when an individual ascends to a high altitude too quickly. Most commonly, symptoms show several hours after arrival. Headaches, loss of appetite (anorexia), nausea, vomiting, lethargy, malaise, and disturbed sleep are the most prevalent symptoms of AMS (Ward 215). A slight fever is also sometimes present.
They are generally considered to be worst on the second and third days but disappear by day five, but may reappear if ascent continues. In this form, it is considered simple or benign AMS. However, severe forms of AMS are known as malignant AMS and are potentially fatal. These are high altitude pulmonary edema (HAPE) and high altitude cerebral edema (HACE). AMS is not related to physical fitness and can affect anyone, though strenuous exercise on the day of arrival is considered a possible risk factor, especially for HAPE. AMS can be prevented by slow ascent and drugs, mostly acetazolamide, usually 1,000 mg a day orally 48 hours prior to ascent and 48 hours after arrival (United States 19).
Though AMS has a clearly defined set of symptoms, there are varying degrees of contraction and seriousness. The Lake Louise scoring system provides a scaled scoring method to determine general severity of AMS, though the diagnosis cannot be made without added factors, such as a recent ascension in height and a period of several hours time before the symptoms presented (Ward 217). The Lake Lousie scoring system can be found here.
There are, of course, other effects of altitude beyond AMS. A loss of weight after arrival at high altitudes is common, but generally stabilizes. This weight loss has been attributed to a reduced diet (possibly connected to the anorexia present in AMS), greater water loss from hyperventilation, and a loss of stored body fat (West 37). Hypoxia in the tissues of the body also results in altered performance both mentally and physically, resulting in a lowered ability to perform tasks effectively or learn new ones, especially at increased altitudes (West 32). However, even after long term exposure to high altitudes, these effects will reverse at lower altitudes eventually, usually within two years at the most.
Sleep disturbance is also a significant concern at high altitudes. In addition to insomnia associated with AMS, there is record of frequent waking and reduced REM sleep and it is common for individuals to be unable to sleep for the first one or two nights at high altitude. More problematic is the characteristic periodic breathing that occurs during sleep at high altitudes. A study by West, et al. in 1986 showed that at 6,300 meters, or about 20,670 feet, there was about an eight second apneic period between breaths. However, these periods may be as long as 10 to 15 seconds (Ward 156).
The treatment for most of these conditions is either treatment of symptoms or removal from the increased altitude, especially in severe cases of AMS. Once an individual returns to a lower altitude, the symptoms, both physiological and mental, should eventually vanish.
Citations
Lake Louise scoring system chart found here: http://www.thepeakinc.com/downloads/lake-louise-score.pdf
United States. UNITED STATES ARMY MEDICAL RESEARCH AND DEVELOPMENT COMMAND. U S ARMY RESEARCH INSTITUTE OF ENVIRONMENTAL MEDICINE. MEDICAL PROBLEMS IN HIGH MOUNTAIN ENVIRONMENTS. Allen Cymerman, Ph.D. and Paul B. Rock, LTC, MC, Feb. 1994. Web. 23 Sept. 2011. <http://www.usariem.army.mil>.
Ward, Michael, James S. Milledge, and John B. West. High Altitude Medicine and Physiology. London: Arnold, 2000. Print.
West, John B., and Sukhamay Lahiri. High Altitude and Man. Bethesda, MD: American Physiological Society, 1984. Print.
United States. UNITED STATES ARMY MEDICAL RESEARCH AND DEVELOPMENT COMMAND. U S ARMY RESEARCH INSTITUTE OF ENVIRONMENTAL MEDICINE. MEDICAL PROBLEMS IN HIGH MOUNTAIN ENVIRONMENTS. Allen Cymerman, Ph.D. and Paul B. Rock, LTC, MC, Feb. 1994. Web. 23 Sept. 2011. <http://www.usariem.army.mil>.
Ward, Michael, James S. Milledge, and John B. West. High Altitude Medicine and Physiology. London: Arnold, 2000. Print.
West, John B., and Sukhamay Lahiri. High Altitude and Man. Bethesda, MD: American Physiological Society, 1984. Print.
