Don’t Go High Up, Danger Is Out There…
Yes, Exposure to high altitude has become commonplace as a result of developments within the last century including air travel, extreme altitude mountaineering and even tourism (e.g. in the Andes). The physiological effects of high altitude are very significant. On Everest, the barometric pressure of the atmosphere falls from sea level by 50% at base camp (5400 m) and 70% at the summit (8848 m). Since the atmosphere is flattened at the poles, due to the centrifugal effect of the earth’s rotation, the atmosphere is thinner at 5800 m on Mount McKinley in Alaska than at the same altitude on Kilimanjaro on the equator. Barometric pressure is also lower in winter than in summer. With the fall in barometric pressure, the proportions of oxygen, nitrogen and carbon dioxide in air do not change, but the pressure of each of these falls in proportion to barometric pressure. Oxygen tension within the lung is further reduced at altitude because the partial pressure of water vapour is related to body temperature and not barometric pressure, and so is proportionately greater at altitude, accounting for only 6% of barometric pressure at sea level, but 19% at 8848 m.
Ascent to altitudes up to 2500 m or travel in a pressurized aircraft cabin is harmless to healthy people. Above 2500 m high-altitude illnesses may occur in previously healthy people, and above 3500 m these become common.
Sudden ascent to altitudes above 6000 m, as experienced by aviators, balloonists and astronauts, may result in decompression illness. Acute Mountain Syndrome is another sickness comprising headache (the principal symptom) together with fatigue, loss of appetite, vertigo, vomiting and difficulty in sleeping. Leg swelling by body fluid may be present. Its cause is not fully understood but it is thought that the oxygen level decreases at brain blood flow and hence the pressure inside the brain rises. Symptoms occur within 6-12 hours of an ascent and vary in severity from trivial to completely incapacitating. The incidence in travelers to 3000 m may be 40-50%. Depending on the rate of ascent, Chronic Mountain sickness can occur. This occurs on prolonged exposure to altitude and has been reported in residents of Colorado, South America and Tibet. Rapid ascent to altitudes above 7000 m may result in loss of consciousness.
Now a days Commercial aircraft usually cruise at 10 000-12 000 m, with the cabin pressurized to an equivalent of around 2400 m. At this altitude, the partial pressure of oxygen is 16 kPa (120 mmHg), leading to a PaO2 in healthy people of 7.0-8.5 kPa (53-64 mmHg). Oxygen level is also reduced, but to a lesser degree. Although well tolerated by healthy people, in patients with respiratory disease this degree of low Oxygen may be dangerous.
yea nice Work