related to AMS per se, but one that probably affects food consumption, is gas expansion in the gastrointestinal tract. The problem obviously persists with continued ascent due to the continued reduction in barometric pressure.
HACE is thought to be a progressive form of AMS with similar symptoms as shown in Table 16-2, albeit on a more severe scale. The incidence of HACE is extremely low but requires immediate attention and medical treatment. From a nutritional standpoint, it should not be a concern for troops at high terrestrial elevations.
Altitude exposure usually leads to significant weight losses in nonacclimatized individuals. Table 16-3 summarizes the weight losses of subjects from several selected studies conducted on high-altitude expeditions, in high-altitude field laboratories, and in hypobaric chambers. This weight loss has been attributed to the novelty of the environment, the effects of altitude-related illnesses, and to the factors shown in Figure 16-7. These factors may or may not be related to altitude-induced illness. Weight loss appears to occur in those whose travel commences at sea level and stabilizes with acclimatization. It does not occur to any appreciable extent in high-altitude natives.
The degree of weight loss is apparently dependent on the altitude and the duration of stay at high altitudes. The direct relationship between the severity of hypoxia and body weight loss has not been demonstrated decisively for humans, but has been demonstrated in animals (Schnakenberg et al., 1971). With acclimatization, weight loss may not be observed unless the altitude is extreme, that is, above 5,000 m (16,404 ft). In fact, Pugh (1962) observed an increase in body weight in one subject on the 1960–1961 Silver Hut Expedition when that subject had a respite of 20 days at 4,500 m (14,764 ft) after descent from 5,800 m (19,029 ft). Even in mountain laboratories at moderate altitudes where diet was controlled, there may not be evidence of an obligatory loss of weight (Butterfield et al., 1992; Kayser et al., 1993).
All of the factors shown in Figure 16-7 can contribute to an overall loss in body weight in deployed soldiers who may not have the benefit of time for acclimatization that is afforded to mountain trekkers and climbers.
Hypoxia-induced diuresis and subliminal thirst (hypodipsia) are usual occurrences in healthy subjects acutely exposed to altitudes similar to the summit of Pikes Peak (4,300 m [14,110 ft]). With individuals having symptoms of AMS, fluid retention that is independent of fluid intake has been observed. These individuals are characterized by a gain in weight. Bärtch et