ABSTRACT
An immutable but usually benign feature of our earthly existence is that the oxygen supply available to us varies depending on the altitude. Oxygen is most plentiful at the highest barometric pressures. Usually this means at sea level, where the barometric pressure is 760 torr.* At locations below sea level, such as the Dead Sea or Death Valley, or in deep mines, oxygen is even more plentiful. As one ascends to higher terrain, artificially levitates oneself in balloons or aircraft, or simulates altitude by sitting in an airlocked decompres sion chamber, the barometric pressure drops, becoming 47 torr at 63,000 ft, at which point no gases are present in alveolar air, only drops of moisture. The reduced barometric pres sure in densely populated areas of the world, such as Denver (altitude 5280 feet, barometric pressure of 622 torr, normal arterial P02, 65 torr), hardly stress normally functioning mech anisms, which provide oxygen for aerobic metabolism. However, when patients living at these same moderate altitudes have disease-limited adaptive mechanisms brought on by a wide range of medical conditions, the coping responses may be sluggish or ineffective, producing, at least, uncomfortable symptoms and in some cases more severe clinical ill ness. An illustrative epidemiological example concerns chronic obstructive pulmonary disease (COPD). A large multihospital Veterans Administration (VA) study of the progno sis of COPD included two participating hospitals located at moderate altitude (Salt Lake City, at 4300 ft, and Albuquerque at 5400 ft). Patients at those altitudes compared with similar patients at sea level had a significantly higher mortality, the precocious develop ment of cor pulmonale, and lower oxygen saturations.
