“…From the medical point of view, there is no obvious geological boundary between high and low altitudes, but from the evidence of plateau-related diseases, it is generally believed that high altitude (HA) refers to the altitude of 1,500 m or above the average sea level (1). It can be divided into three levels: high altitude (1,500-3,500 m), extremely high altitude (3,500-5,500 m), and extreme altitude (>5,500 m) (2).…”