Effect of high altitude on the visual evoked responses in humans on Mt. Everest

Cerebral visual evoked potentials (VEPs) were collected over a 1-year period from the summer of 1983 through the summer of 1984 from 16 members of the American Ultima Thule Everest Expedition at sea level and at altitudes of 7,100 ft, 16,800 ft, and 21,300 ft. VEPs in response to 100 unilateral LED flashes were processed by a modified Nicolet CA-1000 computer of average transients with an analysis time of 250 ms and were recorded by an X-Y plotter. Readings of oxygen saturation, tetrapolar impedance pulmonary plethysmography, and clinical signs and symptoms of acute mountain sickness (AMS) were recorded. The latency of the major waves of the VEPs increased on initial arrival at higher altitude and returned toward base line over time with acclimatization. There were more acute latency changes in individuals who suffered from symptoms of AMS, which reversed with amelioration of symptoms.