HUMAN BIOCLIMATOLOGY

The high altitude environment is one of severe stress for humans. Air pressure is reduced from its sea level value by 30 percent at 3000 m and almost 50 percent at 5000 m (see Table 2.2, 32) and, on average, air temperatures decrease from sea level to the same elevations by about 18 and 30℃, respectively. Other factors include low humidity and increased ultraviolet radiation. Visitors to high altitudes, above about 3000 m, generally notice the oxygen deficiency as a slight breathlessness, especially when undergoing any exertion, and they frequently experience sleep-disordered breathing and/or apnea. Beneficial effects of altitude have also been noted among asthma sufferers due to reduced levels of air pollution and allergens (Hackett, 2001).

The consequences for permanent residents of high altitudes are quite different, however, since they acquire long-term acclimatization. In fact, low temperatures, snow cover and, therefore, limited food resources rather than oxygen deficiency are the dominant controls of human occupancy in the high mountains (Grover, 1974). We will consider first some basic physiological aspects relating to mountain environments in terms of short-term visitors.

Physiological factors and responses

Oxygen deficiency

The difficulties of breathing and symptoms of mountain sickness experienced by early travelers crossing high mountain passes is reported in many historical documents, but scientific explanations only began to be proposed in the late eighteenth century (Houston, 2001).