Effects of simulated high altitude hypoxia and diving on human EEG and subjective evaluations

Abstract

Objective To investigate the effects of simulated high altitude diving and hypoxia on human cerebral function by using alpha attenuation coefficient (AAC) of EEG,event-related potential P300 (ERP P300) and subjective evaluations.Methods Four divers as research subjects were exposed respectively to the altitudes of 3 000,4 000 and 5 200 meters in the hypobaric and hyperbaric chamber for 2 days,during which 30 m and 50 m simulated helium-oxygen mixture gas dives were made for a duration of 60 minutes.Detection and analysis of AAC and auditory-evoked event-related potentials were performed by using recorded EEG.Feelings of fatigue and drowsiness of the divers were detected with visual analogue scale (VAS) and were used as the criteria for subjective evaluation.Results At high altitude exposure,AAC decreased with the elevation of sea levels,and statistical differences could be noted,when it was compared with the data measured at the sea level (P ＜ 0.05).Statistical significance could also be seen,when comparisons were made between different altitudes(P ＜0.05).P300 latency seemed to be prolonged with the elevation of sea level,with the difference at 5 200 m being statistically significant(P ＜ 0.05).However,amplitude seemed to decrease with the elevation of sea levels.Due to limitations of experimental conditions,few research subjects and individual differences between the subjects,the average values tended to decrease,but without statistical significance.Analysis of subjective evaluation indicated that symptoms of hypoxia seemed to be worsened with the elevation of sea levels,and feelings of fatigue and drowsiness increased,which was manifested with the decreased cerebral function,awareness and cognition of the divers.In simulated high altitude diving,AAC tended to increase and subjective evaluation seemed to be better during hyperbaric and hyperoxia exposures.Conclusions When compared with hypoxic conditions,no difference could be noted in AAC during the dives,but there was significant increase in AAC during high altitude hypoxic exposure,indicating that EEG and subjective evaluation tended to return to the baseline level. Key words: Simulated high altitude; Diving; Alpha attenuation coefficient; Subjective evaluation