High-pressure nervous syndrome
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 Template:Convert 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 Template:Convert chamber dive in Marseille.[4]
Symptoms
Symptoms of HPNS include tremors, myoclonic jerking, somnolence, EEG changes,[5] visual disturbance, nausea, dizziness, and decreased mental performance.[1][2]
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 Template:Convert 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 Template:Convert 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]
Prevention
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] There is circumstantial evidence suggesting that a high chamber temperature can aggravate HPNS, and that the temperature should be maintained at a comfortable level.[9]
Including other gases in the Heliox helium–oxygen mixture, such as nitrogen (creating trimix) or hydrogen (producing hydreliox), suppresses the neurological effects.[10][11][12]
Alcohol, anesthetics, and anticonvulsant drugs have had varying results in suppressing HPNS in animals.[1] None are currently in use for humans.Script error: No such module "Unsubst".
In popular culture
HPNS is a plot point in the 1989 James Cameron film The Abyss.Script error: No such module "Unsubst".
HPNS features in episode one of series 3 of State of Happiness (Lykkeland).
See also
- Template:Annotated link
- Template:Annotated link
- Template:Annotated link
- Template:Annotated link
- Template:Annotated link
References
- ↑ a b c d e f g h Script error: No such module "citation/CS1".
- ↑ a b Script error: No such module "Citation/CS1".
- ↑ Script error: No such module "Citation/CS1".
- ↑ Script error: No such module "Citation/CS1".
- ↑ Script error: No such module "Citation/CS1".
- ↑ Script error: No such module "Citation/CS1".
- ↑ Script error: No such module "Citation/CS1".
- ↑ Script error: No such module "Citation/CS1".
- ↑ Template:Cite report
- ↑ Script error: No such module "Citation/CS1".
- ↑ Script error: No such module "Citation/CS1".
- ↑ Script error: No such module "Citation/CS1".