[3] The term high-pressure nervous syndrome was first used by R. W. Brauer in 1968 to describe the combined symptoms of tremor, electroencephalography (EEG) changes, and somnolence that appeared during a 1,189-foot (362 m) chamber dive in Marseille.
[4] Symptoms of HPNS include tremors, myoclonic jerking, somnolence, EEG changes,[5] visual disturbance, nausea, dizziness, and decreased mental performance.
The compression effects may occur when descending below 500 feet (150 m) at rates greater than a few metres per minute, but reduce within a few hours once the pressure has stabilised.
[1] The effect of dissolved helium on an embedded trans-membrane channel has also been studied by molecular modeling tools.
[1][8] Including other gases in the Heliox helium–oxygen mixture, such as nitrogen (creating trimix) or hydrogen (producing hydreliox), suppresses the neurological effects.