THE HIGH-TERRESTRIAL ENVIRONMENT
PART IV BEGINS BY EXPLORING THE PHYSIOLOGICAL and mental responses that uniquely characterize high altitudes. Chapter 16 details the physiological and pathological effects of high-altitude exposure. An initial weight loss accompanies the ascent to altitude because of increased water losses and decreased energy intake relative to expenditure. Altitude-related illnesses, such as acute mountain sickness and high-altitude cerebral edema, may cause further complications because they affect nutrition. Chapter 17 reviews the effects of lowered oxygen transport on physical performance as well as cardiac, hematologic, and nervous system responses at high altitudes. In Chapter 18, fluid metabolism at high altitudes is discussed. The literature presents conflicting data due to the differences in methodology and the presence of variables such as the effects of altitude-related sickness. Water retention contributes to the development of these illnesses, and exercise stimulates the accumulation of body water and electrolytes.
At high altitudes, diuresis, decline in appetite, and increase in basal energy needs contribute to weight loss. Chapter 19 finds that adequate energy intake can eliminate this problem, as well as decrease the diuresis that results from acute altitude exposure. Carbohydrate is the metabolic fuel that ensures adequate energy intake. Total energy requirements at high altitude are discussed in Chapter 20. The type and duration of physical activity, preexisting
energy stores, and environmental conditions determine these energy needs. Because the energy requirements for work at high altitudes are higher and appetite tends to decline, energy intakes are often inadequate to meet these increases.
Chapter 21 presents evidence suggesting that there is increased oxidative stress at high altitudes, which impairs blood flow and physical performance. Inadequate levels of antioxidants may impair metabolic functions at altitude, and some studies show that vitamin E is beneficial.