{{Short description|Disorder from breathing helium based gas at high ambient pressure}}
'''High-pressure nervous syndrome''' ('''HPNS''' – also known as '''high-pressure neurological syndrome''') is a neurological and physiological diving disorder which can result when a diver descends below about {{convert|500|ft|m|-1}} using a breathing gas containing helium. The effects experienced, and the severity of those effects, depend on the rate of descent, the depth and the percentage of helium.<ref name=Brubakk>{{cite book |title=Bennett and Elliott's physiology and medicine of diving, 5th Rev ed |editor1-last=Brubakk |editor1-first=Alf O. |editor1-link=Alf O. Brubakk |editor2-last=Neuman |editor2-first=Tom S |year=2003 |publisher=Saunders |location=United States |isbn=0-7020-2571-2 |last1=Bennett |first1=Peter B |last2=Rostain |first2=Jean Claude |chapter=The High Pressure Nervous Syndrome |pages=323–57}}</ref>
"Helium tremors" were described in 1965 by Royal Navy physiologist Peter B. Bennett.<ref name=Brubakk/><ref name=Bennett>{{cite journal |last=Bennett |first=P. B. |title=Psychometric impairment in men breathing oxygen-helium at increased pressures |journal=Royal Navy Personnel Research Committee, Underwater Physiology Subcommittee Report No. 251 |year=1965 |location=London }}</ref> Soviet scientist G. L. Zal'tsman first reported on helium tremors in his experiments from 1961. These reports were not available in the West until 1967.<ref>{{cite journal |last=Zal'tsman |first=G. L. |title=Psychological principles of a sojourn of a human in conditions of raised pressure of the gaseous medium (in Russian, 1961) |journal=English Translation, Foreign Technology Division. AD655 360 |year=1967 |location=Wright Patterson Air Force Base, Ohio }}</ref>
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 {{convert|1189|ft|m|adj=on}} chamber dive in Marseille.<ref>{{cite journal |last=Brauer |first=R. W. |title=Seeking man's depth level |journal=Ocean Industry |volume=3 |pages=28–33 |year=1968 |location=London }}</ref>
==Symptoms== Symptoms of HPNS include tremors, myoclonic jerking, somnolence, EEG changes,<ref>{{cite journal |last=Brauer |first=R. W. |author2=S. Dimov |author3=X. Fructus |author4=P. Fructus |author5=A. Gosset |author6= R. Naquet. |title=Syndrome neurologique et electrographique des hautes pressions |journal=Rev Neurol |volume=121 |issue=3 |pages=264–5 |year=1968 |pmid=5378824 |location=Paris }}</ref> visual disturbance, nausea, dizziness, and decreased mental performance.<ref name=Brubakk/><ref name=Bennett/>
==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 {{convert|500|ft|m|-1}} 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 {{convert|1000|ft|m|-1}} and remain regardless of the time spent at that depth. All effects are completely reversible on ascent to shallower depths.<ref name=Brubakk/>
The susceptibility of divers and animals to HPNS varies over a wide range depending on the individual, but has little variation between different dives by the same diver.<ref name=Brubakk/>
The effect of dissolved helium on an embedded trans-membrane channel has also been studied by molecular modeling tools. Those suggest that helium might cause substantial lipid membrane distortion. The high hydrostatic pressure itself has a less damaging influence on the membrane, reducing molecular volumes, but leaving the molecular boundary intact.<ref>{{cite journal |last1=Bliznyuk |first1=Alice |last2=Grossman |first2=Yoram |last3=Moskovitz |first3=Yevgeny |title=The effect of high pressure on the NMDA receptor: molecular dynamics simulations |journal=Scientific Reports |date=25 July 2019 |volume=9 |issue=1 |page=10814 |doi=10.1038/s41598-019-47102-x |publisher=Nature Research|pmid=31346207 |pmc=6658662 |bibcode=2019NatSR...910814B |doi-access=free }}</ref>
==Prevention== It is likely that HPNS cannot be entirely prevented but there are effective methods to delay or change the development of the symptoms.<ref name=Brubakk/><ref>{{cite journal |last=Hunger |first=W. L. Jr. |first2=P. B. |last2=Bennett |title=The causes, mechanisms and prevention of the high pressure nervous syndrome |journal=Undersea Biomed. Res. |volume=1 |issue=1 |pages=1–28 |year=1974 |issn=0093-5387 |oclc=2068005 |pmid=4619860 }}</ref>
Slow rates of compression, or adding stops to the compression, have been found to prevent large initial decrements in performance.<ref name=Brubakk/><ref>{{cite journal |last=Bennett |first=P. B. |first2=R. |last2=Coggin |first3=M. |last3=McLeod |title=Effect of compression rate on use of trimix to ameliorate HPNS in man to 686 m (2250 ft) |journal=Undersea Biomed. Res. |volume=9 |issue=4 |pages=335–51 |year=1982 |issn=0093-5387 |oclc=2068005 |pmid=7168098 }}</ref> There is circumstantial evidence suggesting that a high chamber temperature can aggravate HPNS, and that the temperature should be maintained at a comfortable level.<ref name="NUI" >{{cite report |url=https://www.havtil.no/contentassets/04882bf9c4054c0989f0fd70fc8c05e6/2022_1121-prosjektrapport-compression-and-excursion-parameters-for-saturation-diving.pdf |title=Compression and excursion parameters for saturation dives 0-250 msw |publisher=NUI |work=2023-69 |edition=Revision 1 |date=22 January 2024 |archive-date=24 January 2025 |access-date=14 June 2025 |archive-url=https://web.archive.org/web/20250124103050/https://www.havtil.no/contentassets/04882bf9c4054c0989f0fd70fc8c05e6/2022_1121-prosjektrapport-compression-and-excursion-parameters-for-saturation-diving.pdf |url-status=live }}</ref>
Including other gases in the heliox helium–oxygen mixture, such as nitrogen (creating trimix) or hydrogen (producing hydreliox), suppresses the neurological effects.<ref name="vigreux1970">{{cite journal |last=Vigreux |first=J. |title=Contribution to the study of the neurological and mental reactions of the organism of the higher mammal to gaseous mixtures under pressure |journal=MD Thesis |year=1970 |location=Toulouse University }}</ref><ref name="fife1979">{{cite journal |last=Fife |first=W. P. |title=The use of Non-Explosive mixtures of hydrogen and oxygen for diving |volume=TAMU-SG-79-201 |journal=Texas A&M University Sea Grant |year=1979 }}</ref><ref>{{cite journal |last=Rostain |first=J. C. |author2=Gardette-Chauffour, M. C. |author3=Lemaire, C. |author4= Naquet, R. |title=Effects of a H2-He-O2 mixture on the HPNS up to 450 msw |journal=Undersea Biomedical Research |volume=15 |issue=4 |pages=257–70 |year=1988 |issn=0093-5387 |oclc=2068005 |pmid=3212843 |url=http://archive.rubicon-foundation.org/2487 |archive-url=https://web.archive.org/web/20081206035912/http://archive.rubicon-foundation.org/2487 |url-status=usurped |archive-date=December 6, 2008 |access-date=2008-04-07 }}</ref>
Alcohol, anesthetics, and anticonvulsant drugs have had varying results in suppressing HPNS in animals.<ref name=Brubakk/> None are {{ As of | 2008 | 4 | alt= currently}} in use for humans.{{citation needed|date=September 2013}}
==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== * {{annotated link|Barotrauma}} * {{annotated link|Compression arthralgia}} * {{annotated link|Decompression sickness}} * {{annotated link|Nitrogen narcosis}} * {{annotated link|Oxygen toxicity}}
== References ==
<references>
</references>
{{underwater diving|divmed}}
{{DEFAULTSORT:High-Pressure Nervous Syndrome}} Category:Underwater diving disorders Category:Underwater diving hazards Category:Underwater diving physiology