High pressure nervous syndrome
Encyclopedia
High-pressure nervous syndrome (HPNS – also known as high-pressure neurological syndrome) is a neurological and physiological diving disorder that results when a commercial diver or scuba diver descends below about 500 feet (152.4 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 to describe the combined symptoms of tremor, electroencephalography
(EEG) changes, and somnolence
that appeared during a 1189 feet (362.4 m) chamber dive in Marseilles.
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.
(creating trimix) or hydrogen
(hydreliox
) suppresses the neurological effects.
"Helium tremors" were first widely described in 1965 by Royal Navy
Royal Navy
The Royal Navy is the naval warfare service branch of the British Armed Forces. Founded in the 16th century, it is the oldest service branch and is known as the Senior Service...
physiologist Peter B. Bennett
Peter B. Bennett
Peter B. Bennett is the founder and former president and CEO of the Divers Alert Network , a non-profit organization devoted to assisting scuba divers in need. He is a professor of anesthesiology at Duke University Medical Center, and is currently the Senior Director of the Center for Hyperbaric...
, who also founded the Divers Alert Network
Divers Alert Network
The Divers Alert Network is a non-profit 501 organization devoted to assisting divers in need. The Research department conducts significant medical research on recreational scuba diving safety...
. 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 to describe the combined symptoms of tremor, electroencephalography
Electroencephalography
Electroencephalography is the recording of electrical activity along the scalp. EEG measures voltage fluctuations resulting from ionic current flows within the neurons of the brain...
(EEG) changes, and somnolence
Somnolence
Somnolence is a state of near-sleep, a strong desire for sleep, or sleeping for unusually long periods . It has two distinct meanings, referring both to the usual state preceding falling asleep, and the chronic condition referring to being in that state independent of a circadian rhythm...
that appeared during a 1189 feet (362.4 m) chamber dive in Marseilles.
Symptoms
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 500 feet (152.4 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 1000 feet (304.8 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.
Prevention
It is likely that HPNS can not be entirely prevented but there are effective methods to delay or change the development of the symptoms.Rate of Compression
Utilizing slow rates of compression or adding stops to the compression have been found to prevent large initial decrements in performance.Breathing Mixture
Including other gases in the mix, such as nitrogenNitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
(creating trimix) or hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
(hydreliox
Hydreliox
Hydreliox is an exotic breathing gas mixture of helium, oxygen and hydrogen.It is used primarily for research and scientific deep diving, usually below . Below this depth, extended breathing of heliox gas mixtures may cause high pressure nervous syndrome . Two gas mixtures exist that attempt to...
) suppresses the neurological effects.
Drugs
Alcohol, anesthetics and anticonvulsant drugs have had varying results in suppressing HPNS with animals. None are currently in use for humans.External links
- Select publications about HPNS hosted by the Rubicon FoundationRubicon FoundationRubicon Foundation, Inc. is a non-profit organization devoted to contributing to the interdependent dynamic between research, exploration, science and education. The foundation, started in 2002, is located in Durham, North Carolina and is primarily supported by donations and grants. Funding has...