ABSTRACT
Most of the medical problems that occur at high altitude are caused by the low partial pressure of oxygen in the atmosphere which in turn is due to the decrease in barometric pressure as altitude increases. The relationship between barometric pressure and altitude is therefore important, especially in regions of the world such as the Andes and Himalayas where large numbers of people reside at high altitude. Recent work has clarified the pressure-altitude relationship with much better accuracy than previously. Considerable confusion occurred in the past by assuming that the relationship follows the standard atmosphere. In fact, the pressures are usually substantially higher at a given altitude because the relationship between barometric pressure and altitude is latitude-dependent, and most of the high mountains of the world are relatively near the equator. At extreme altitudes, the variation of barometric pressure with season is believed to be sufficient to affect human performance. This is particularly true of the summit of Mount Everest where climbers are near the limit of tolerance to hypoxia. Other atmospheric factors, such as temperature, humidity and solar radiation, are also important.
