High-pressure nervous syndrome
High-pressure nervous syndrome (HPNS – also known as high-pressure neurological syndrome) is a neurological and physiological diving disorder that results when a diver descends below about 500 feet (150 m) while breathing a helium–oxygen mixture. The effects depend on the rate of descent and the depth. HPNS is a limiting factor in future deep diving.
"Helium tremors" were first widely described in 1965 by Royal Navy physiologist Peter B. Bennett, who also founded the Divers Alert Network. Russian scientist G. L. Zal'tsman also reported on helium tremors in his experiments from 1961. However these reports were not available in the West until 1967.
The term high pressure nervous syndrome was first used by 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.
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.
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.
Rate of Compression 
Breathing Mixture 
Alcohol, anesthetics and anticonvulsant drugs have had varying results in suppressing HPNS with animals. None are currently in use for humans.
See also 
- Bennett, Peter B; Rostain, Jean Claude (2003). "The High Pressure Nervous Syndrome". In Brubakk, Alf O; Neuman, Tom S. Bennett and Elliott's physiology and medicine of diving, 5th Rev ed. United States: Saunders. pp. 323–57. ISBN 0-7020-2571-2.
- 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).
- 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).
- Brauer, R. W. (1968). "Seeking man's depth level". Ocean Industry (London) 3: 28–33.
- Brauer, R. W.; S. Dimov; X. Fructus; P. Fructus; A. Gosset; R. Naquet. (1968). "Syndrome neurologique et electrographique des hautes pressions". Rev Neurol (Paris) 121 (3): 264–5. PMID 5378824.
- Hunger Jr, W. L.; 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. Retrieved 2008-04-07.
- 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. Retrieved 2008-04-07.
- 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).
- 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.
- 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. Retrieved 2008-04-07.