High-pressure nervous syndrome

Symptoms of HPNS include tremors, myoclonic jerking, somnolence, EEG changes, visual disturbance, nausea, dizziness, and decreased mental performance. ==Causes==

HPNS has two components, one resulting from the speed of compression and the other from the absolute pressure. The compression effects may occur when descending below at rates greater than a few metres per minute, but reduce within a few hours once the pressure has stabilised. The effects from depth become significant at depths exceeding and remain regardless of the time spent at that depth. All effects are completely reversible on ascent to shallower depths. ==Prevention==

It is likely that HPNS cannot be entirely prevented but there are effective methods to delay or change the development of the symptoms. Slow rates of compression, or adding stops to the compression, have been found to prevent large initial decrements in performance. There is circumstantial evidence suggesting that a high chamber temperature can aggravate HPNS, and that the temperature should be maintained at a comfortable level. Including other gases in the heliox helium–oxygen mixture, such as nitrogen (creating trimix) or hydrogen (producing hydreliox), suppresses the neurological effects. Alcohol, anesthetics, and anticonvulsant drugs have had varying results in suppressing HPNS in animals. None are in use for humans. ==In popular culture==

HPNS is a plot point in the 1989 James Cameron film The Abyss. HPNS features in episode one and two of series 3 of State of Happiness (Lykkeland). in Mission: Impossible – The Final Reckoning, it is mentioned that HPNS will occur during a dive due to the extremely fast descent needed for a mission. ==See also==