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 500 feet (150 m) 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.[1]

"Helium tremors" were described in 1965 by Royal Navy physiologist Peter B. Bennett.[1][2] 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.[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.[1][2]


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 500 feet (150 m) 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 1,000 feet (300 m) and remain regardless of the time spent at that depth. All effects are completely reversible on ascent to shallower depths.[1]

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.[1]

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.[6]


It is likely that HPNS cannot be entirely prevented but there are effective methods to delay or change the development of the symptoms.[1][7]

Slow rates of compression, or adding stops to the compression, have been found to prevent large initial decrements in performance.[1][8]

Including other gases in the Heliox helium–oxygen mixture, such as nitrogen (creating trimix) or hydrogen (producing hydreliox), suppresses the neurological effects.[9][10][11]

Alcohol, anesthetics, and anticonvulsant drugs have had varying results in suppressing HPNS in animals.[1] None are currently in use for humans.[citation needed]

In popular culture

HPNS is a plot point in the 1989 James Cameron film The Abyss.

See also


  1. ^ a b c d e f g h Bennett, Peter B; Rostain, Jean Claude (2003). "The High Pressure Nervous Syndrome". In Brubakk, Alf O.; Neuman, Tom S (eds.). Bennett and Elliott's physiology and medicine of diving, 5th Rev ed. United States: Saunders. pp. 323–57. ISBN 0-7020-2571-2.
  2. ^ a b Bennett, P. B. (1965). "Psychometric impairment in men breathing oxygen-helium at increased pressures". Royal Navy Personnel Research Committee, Underwater Physiology Subcommittee Report No. 251. London.
  3. ^ Zal'tsman, G. L. (1967). "Psychological principles of a sojourn of a human in conditions of raised pressure of the gaseous medium (in Russian, 1961)". English Translation, Foreign Technology Division. AD655 360. Wright Patterson Air Force Base, Ohio.
  4. ^ Brauer, R. W. (1968). "Seeking man's depth level". Ocean Industry. 3. London: 28–33.
  5. ^ Brauer, R. W.; S. Dimov; X. Fructus; P. Fructus; A. Gosset; R. Naquet. (1968). "Syndrome neurologique et electrographique des hautes pressions". Rev Neurol. 121 (3). Paris: 264–5. PMID 5378824.
  6. ^ Bliznyuk, Alice; Grossman, Yoram; Moskovitz, Yevgeny (25 July 2019). "The effect of high pressure on the NMDA receptor: molecular dynamics simulations". Scientific Reports. 9 (1). Nature Research: 10814. Bibcode:2019NatSR...910814B. doi:10.1038/s41598-019-47102-x. PMC 6658662. PMID 31346207.
  7. ^ Hunger, W. L. Jr.; P. B. Bennett. (1974). "The causes, mechanisms and prevention of the high pressure nervous syndrome". Undersea Biomed. Res. 1 (1): 1–28. ISSN 0093-5387. OCLC 2068005. PMID 4619860. Archived from the original on 2010-12-25. Retrieved 2008-04-07.((cite journal)): CS1 maint: unfit URL (link)
  8. ^ Bennett, P. B.; R. Coggin; M. McLeod. (1982). "Effect of compression rate on use of trimix to ameliorate HPNS in man to 686 m (2250 ft)". Undersea Biomed. Res. 9 (4): 335–51. ISSN 0093-5387. OCLC 2068005. PMID 7168098. Archived from the original on July 8, 2012. Retrieved 2008-04-07.((cite journal)): CS1 maint: unfit URL (link)
  9. ^ Vigreux, J. (1970). "Contribution to the study of the neurological and mental reactions of the organism of the higher mammal to gaseous mixtures under pressure". MD Thesis. Toulouse University.
  10. ^ Fife, W. P. (1979). "The use of Non-Explosive mixtures of hydrogen and oxygen for diving". Texas A&M University Sea Grant. TAMU-SG-79-201.
  11. ^ Rostain, J. C.; Gardette-Chauffour, M. C.; Lemaire, C.; Naquet, R. (1988). "Effects of a H2-He-O2 mixture on the HPNS up to 450 msw". Undersea Biomedical Research. 15 (4): 257–70. ISSN 0093-5387. OCLC 2068005. PMID 3212843. Archived from the original on December 6, 2008. Retrieved 2008-04-07.((cite journal)): CS1 maint: unfit URL (link)