High-pressure neurologic syndrome

K K Jain MD (Dr. Jain is a consultant in neurology and has no relevant financial relationships to disclose.)
Originally released December 29, 1997; last updated September 15, 2016; expires September 15, 2019

This article includes discussion of high-pressure neurologic syndrome, helium tremors, and high-pressure nervous syndrome. The foregoing terms may include synonyms, similar disorders, variations in usage, and abbreviations.

Overview

High-pressure neurologic syndrome is a condition encountered in deep-sea diving beyond a depth of 100 meters and is characterized by several neurologic, as well psychiatric, symptoms and signs. The effects are primarily due to excessive atmospheric pressure on different structures in the central nervous system. Neurophysiological and neurochemical changes, based on animal experimental studies, are described. This syndrome needs to be differentiated from inert gas narcosis, decompression sickness, and oxygen poisoning. No definite treatment exists, but barbiturates, anticonvulsant drugs, anesthetics, as well as nonanesthetic compounds have been used in management of this syndrome.

Key points

 

• Clinical features of high-pressure neurologic syndrome vary according to the depth (beyond 100 meters) and the gas mixture used.

 

• Although there are several symptoms and signs, there is no evidence of permanent neurologic sequelae or histopathologic changes in the brain resulting from high-pressure neurologic syndrome.

 

• Because of different approaches to management, high pressure neurologic syndrome needs to be differentiated from inert gas narcosis, decompression sickness, and oxygen toxicity.

 

• The pharmacological approach is based on the resemblance of high-pressure neurologic syndrome to serotonin syndrome, and 5-HT1A receptor antagonists may provide a preventive approach.

Historical note and terminology

High-pressure neurologic syndrome is a condition encountered in deep-sea diving beyond a depth of 100 meters, a feat that is made possible by the breathing of special gas mixtures such as helium and oxygen (heliox). It is characterized by neurologic, psychological, and electroencephalographic abnormalities. In 1967, Bennett described a decline of mental performance and tremors following dives to between 200 and 250 meters and termed this condition "helium tremors" (Bennett 1967). He was unaware of the fact that the same phenomenon had been observed in Russia earlier by Zaltsman, who used the same term to describe it (Zaltsman 1968). High-pressure neurologic syndrome, characterized by tremors and EEG changes, was first observed in divers who dove deeper than 300 meters (Brauer et al 1969). Most of the basic research in this area has been done on experimental animals. The term "neurologic" is preferred to the term "nervous" (original translation of nerveux, as described in French).

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