High Altitude: The scientific and medical aspects
High altitude is defined as the height above which the atmospheric pressure is less than 760 mmHg. It generally refers to elevations between 5,000 and 8,000 meters (about 16,500 to 26,250 feet). Although some people live permanently at high altitudes, most of the world’s population lives at or near sea level. People who travel to high altitudes for work or recreation make up a small but important group. For example, mountaineers often climb to altitudes greater than 8,000 meters (26,250 feet) while pilots may fly aircraft at altitudes up to 12,500 meters (41,010 feet).
The effects of altitude on humans are caused by reduced air pressure and lower oxygen levels at higher elevations. These conditions can lead to several health problems including:
• Acute mountain sickness (AMS) – a condition that usually occurs above 2,400 meters (about 8,000 feet). Symptoms include headache, nausea and vomiting, fatigue, lightheadedness and difficulty sleeping. Most people acclimatize within a few days and do not experience serious symptoms. However , some people develop more severe forms of AMS known as high-altitude cerebral edema (HACE) or high-altitude pulmonary edema(HAPE). HACE is characterized by confusion , loss of coordination ,and eventually coma . HAPE is marked by cough ,shortness of breath upon exertion ,and eventual respiratory failure . Both conditions are life threatening and require immediate descent .
• Hypoxia – a condition that results when the body tissues are deprived of oxygen . Hypoxia can cause headaches ,fatigue ,shortness of breath ,nausea ,insomnia and dizziness . It can also lead to more serious conditions such as HACE or HAPE .
High altitude presents many challenges for the human body . The first challenge is simply getting enough oxygen into the bloodstream . At sea level ,each breath delivers about 21 percent oxygen ; however this percentage decreases with elevation so that at 4559 meters(about 15 000feet ) only about 12 percentoxygenis available in each breath In addition blood carries less oxygen at high altitude because hemoglobin molecules have a harder time bindingto oxygen molecules in low -pressure environments Another problem associated with low partial pressuresof inspired gasesis hypoventilationor shallow breathing Many visitors to high altitude failto increase their breathing rate adequatelyto compensatefor the decrease ininspired gas concentrations This relative hypoventilation resultsin retentionof carbon dioxide which promotes drowsiness Ascentto even moderatelyhigh altitudethereforerequirescarefulmonitoringof breathingpatternsand frequentreststo maintain an adequatelevelof ventilation To further complicate matters ascentto highelevationscan resultindecreasedappetiteand fluidintake bothof which contribute toundernutrition Dehydrationalsobecomesa concernas urine outputincreases insomeindividualsdespitelow total fluid intake Allofthesefactorscombine topotentiallyimpedeperformanceat highelevation Finallyhighaltitudepresentsseveralcold weatherchallengesbecause temperaturesgenerallydecreasewith increasingelevation Humidityalso dropsso that perspirationevaporatesmore quickly leadingtothe sensationoffeelingchilled Additionallywind chillcan becomeaproblemat highelevation exacerbatingthe cold weathereffects Highaltitudealso predisposesindividualstoSolar radiationexposurebecause thereis les atmospherebetweenyouand the suntoprotectyou from ultravioletlight Furthermorethinnerairprovideslessbufferingfrom potentiallydamagingtemperatureextremes So althougha sunny daycan feelquite pleasantattopofthemountainit mightactuallybe causinglongterm cell damagewithout youeven realizingit