高所における大脳事象関連電位および聴覚誘発電位の変化

Abstract

人が平地から標高5000mを越える高所に移動すると頭痛, 嘔吐, 不眠といった自律神経系の機能障害に起因する症状に加えて, 感覚および運動機能障害, 判断力, 記憶力の低下等の大脳および小脳の機能障害が現れる. 本調査は, 電気生理学的手法を用いて, これらの脳機能障害のメカニズムを解明するための手がかりを得ることが目的である.

It is well known that the hypoxic environment produced by sojourn at high altitudes often induces the disorders in the sensory and motor system of the brain as well as behavioral and physiological changes such as anorexia nausea or insomnia. These symptoms may be produced mainly by combined effect of hypoxia and hypothermia at high altitudes. The purpose of this study is to find the changes in the electrical activities of the human brain at high altitudes occurring in association with brain symptoms and disorders. Twenty one subjects were selected from the members of the Kyoto University Himalayan Medical Expedition in 1990. They spent about two or three months at high altitudes above 5000 meters. Recordings of the event related potentials (ERP) which is referred to P3 or P300, and auditory evoked potentials (AEP) were made at sea level and at high altitudes, usually at the base camp. The subject concentrated to a tone, and responded by pressing a push-button with the thumb. Paired tones separated by an interstimulus interval of 1-4 seconds were given to the subjects required to respond to the second tone. The electroencephalogram (EEG) was recorded from silver-chloride disc electrodes at vertex (Cz), with left earlobe as reference. The right earlobe was connected to the ground, usually. The amplified EEG was stored on magnetic tapes using a frequency modulated tape recorder for off-line analysis by an averaging computer after returning to our laboratories. Individual potentials were averaged over 30-50 trials. In 13 subjects significant decrease in ERP (P3) at high altitudes was observed compared with control recordings at sea level. Seven subjects suffered from the brain syndrome. Mean values of the P3 were 7.9 + 5.1 uV at high altitude and 18.5 + 9.2 uV (N=13) at sea level. Significant decrease in AEP was also observed. Mean values of the AEP were 9.6 + 5.8 uV at high altitude and 15.8 + 6.2 uV (N=21) at sea level. It was inferred that ERP is more sensitive to the hypoxic environment compared with AEP.