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FIGURE 16-5 Differential response of urinary norepinephrine (NE) and epinephrine (E) during 7 days of exposure to 4,300 m (14,110 ft). SOURCE: Adapted from Burse et al. (1987).

compensated respiratory alkalosis, the increased real hematocrit, the restoration of normal blood flow distribution, and altered metabolic pathways.

The degree of adaptability of the human organism to very high terrestrial elevations is best exemplified by the natives of the Andes mountains. From present-day observations and historical records of South American Indians, there is evidence that oxygen concentrations as low as 10.5 percent (equivalent to 5,500 m or 18,045 ft) can be tolerated to do heavy physical work as long as the natives sleep at a lower altitude. High-altitude natives can apparently maintain a routine of working in mines at 5,500 m (18,045 ft) and sleeping at lower elevations for extended periods of time without marked deterioration.

For sojourners to high altitudes without any acclimatization, this level of exposure would result in marked deterioration and illness. The ability for newcomers to acclimatize adequately to a moderate altitude is dependent on the rate of ascent and the time allowed for acclimatization. Figure 16-6 illustrates the relative time, magnitude, and direction of changes at the respiratory, circulatory, and cellular levels with respect to their relationship to general health and performance at 4,267 to 4,572 m (14,000 to 15,000 ft).

Several illnesses can occur with ascent to altitude. Of these, only two are of real concern for the purposes of this book. A brief discussion of these illnesses is warranted because they affect nutrition. These illnesses are termed acute mountain sickness (AMS) and high-altitude cerebral edema (HACE).

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