injuries poisoning
Altitude Illness
Pathophysiology of Altitude Illness
Whereas severe acute hypoxemia can cause altered central nervous system function within a matter of minutes, acute altitude illness develops anywhere from 1 to 5 days after ascent to a given elevation. The pathogenesis of acute mountain sickness (AMS) and high-altitude cerebral edema (HACE) remain unclear despite considerable research in this area. The diseases likely develop as a result of the same underlying pathophysiology and fall on a continuum of severity, with HACE representing the extreme of the spectrum. AMS may involve activation of the trigeminovascular system due to a variety of stimuli, while HACE involves blood-brain barrier leakage and increased intracranial pressure. High-altitude pulmonary edema (HAPE) is caused by hypoxia-induced elevation of pulmonary artery pressure which causes interstitial and alveolar pulmonary edema, resulting in impaired oxygenation. Small-vessel hypoxic vasoconstriction is patchy, causing elevated pressure, capillary wall damage, and capillary leakage in less constricted areas. Other factors, such as sympathetic overactivity, may also be involved. Long-time high-altitude residents can develop HAPE when they return after a brief stay at low altitude, a phenomenon referred to as reentry pulmonary edema. Recent reports suggest that long-term high-altitude residents can also develop noncardiogenic pulmonary edema—referred to as high-altitude resident HAPE—even if they do not descend to and then return from a lower elevation. Acclimatization is an integrated series of responses that allow the body to tolerate the hypoxia at high altitude. Most people acclimatize reasonably well to altitudes of up to 3000 m (10,000 ft) within a few days. The higher the altitude, the longer acclimatization takes. However, no one can fully acclimatize to long-term residence at altitudes>5100 m (>17,000 ft). but also causes Respiratory Alkalosis . Blood pH tends to normalize within days as bicarbonate is excreted in urine; as pH normalizes, ventilation can increase further. Cardiac output increases initially and returns to baseline values over time; red blood cell mass and tolerance for aerobic work also increase over a period of several weeks. 