The term altitude does not have a precise scientific definition (see section on epidemiology for definitions of work). Physiologically, elevated altitudes are generally accepted as altitudes above 2700 m. At these altitudes, arterial oxygen partial pressure (PaO2) is about 66 mm Hg, giving an arterial oxygen saturation of hemoglobin (SaO2) of 92%. During sleep, the resulting hypoventilation produces a new drop of PaO2, and SaO2 drops significantly due to the sigmoid form of the oxygen dissociation curve of hemoglobin, leading to significant tissue hypoxia. Cardiorespiratory changes are usually seen just above these altitudes. The term extreme altitude (altitudes above 5800M) also has a physiological meaning. Long-term human survival above these heights is not possible, since physiological changes in acclimatization can not compensate for the severity of hypoxia.
High Altitude Physics Physical Education Essay
High altitudes, compared to sea level environments, have higher levels of ionizing and non-ionizing radiation and lower levels of temperature and barometric pressures. Of these factors, reduced barometric pressure is unique to high altitude and is the main factor involved in acclimatization and pathogenesis of high altitude disturbances. The percentage of oxygen remains the same at all altitudes. However, the drop in ambient barometric pressure results in progressively low partial pressures of oxygen with increased altitude. Figure 1.1 gives the relation of altitude, barometric pressure and oxygen partial pressure.
A high environmental risk at high altitude associated with hypoxia is cold. There is approximately 10 C of temperature drop per 150 m altitude. Although low temperatures are not unique to high altitude, the combined effects of hypoxia and cold change the course of injury related to freezing cold and cold in terms of severity and incidence. The high wind speeds further aggravate the cold due to the wind cooling factor.
Mountain air is generally drier than sea level air. This drop in humidity is directly proportional to the drop in temperature. Dry air has important physiological effects. Loss of insensitive water due to evaporation is increased. Hyperventilation observed at high altitudes further increases water loss and the resulting dehydration predisposes to thrombosis. The combination of low temperature and low humidity is subjectively unpleasant.
Solar and ionizing radiation is significantly higher at high altitudes. Sensitivity to radio tissue increases with increased oxygen tension. The potentially harmful effects of increased ionizing radiation are partially offset by the hypoxia observed at high altitude. The characteristic changes occur in the exposed skin that was denominated Dermatopatia of high altitude. These changes are similar to the histological changes observed in the skin on prolonged exposure to solar radiation.