bennett ( 1975 ) reported that signs and symptoms of the high pressure nervous syndrome ( hpns ) appeared including nausea , dizziness , tremors of the hands and arms , increased slow wave activity in electroencephalogram , especially in the theta band ( 4-7 hz ) with depression of alpha ( 8-13 hz ) and beta ( 20 hz and higher ) on compression with oxygen-helium to depths greater than 500 ft ( 16 ata ) .
C0019537
high pressure nervous
C0018880
helium