science

High-pressure nervous syndrome

High-pressure nervous syndrome is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand High-pressure nervous syndrome rather than just read about it. In short: 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. "Helium tremors" were described in 19…

Key takeaways

High-pressure nervous syndrome belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect High-pressure nervous syndrome to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of High-pressure nervous syndrome from memory before moving on to harder problems.

Reference excerpt

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. "Helium tremors" were described in 1965 by Royal Navy physiologist Peter B. Bennett. 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. 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.

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 (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. 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. 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.

Prevention It is likely that HPNS cannot be entirely prevented but there are effective methods to delay or change the development of the symptoms. Slow rates of compression, or adding stops to the compression, have been found to prevent large initial decrements in performance. There is circumstantial evidence suggesting that a high chamber temperature can aggravate HPNS, and that the temperature should be maintained at a comfortable level. Including other gases in the heliox helium–oxygen mixture, such as nitrogen (creating trimix) or hydrogen (producing hydreliox), suppresses the neurological effects. Alcohol, anesthetics, and anticonvulsant drugs have had varying results in suppressing HPNS in animals. None are currently in use for humans.

In popular culture HPNS is a plot point in the 1989 James Cameron film The Abyss. HPNS features in episode one and two of series 3 of State of Happiness (Lykkeland). in Mission: Impossible – The Final Reckoning, it is mentioned that HPNS will occur during a dive due to the extremely fast descent needed for a mission.

See also Barotrauma – Injury due to pressure difference between gas filled space and adjoining tissue Compression arthralgia – Joint pain caused by fast compression to high ambient pressure Decompression sickness – Disorder caused by dissolved gases forming bubbles in tissues Nitrogen narcosis – Narcotic effects of respiratory nitrogen Oxygen toxicity – Toxic effects of breathing oxygen at high partial pressures

References

Worked examples

Example 1 — a first encounter with High-pressure nervous syndrome

Start with the simplest possible case. Write down what High-pressure nervous syndrome claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to High-pressure nervous syndrome before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about High-pressure nervous syndrome ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of High-pressure nervous syndrome

In research: High-pressure nervous syndrome appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses High-pressure nervous syndrome in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: High-pressure nervous syndrome is common in secondary-school and first-year university syllabi. It links to neighbouring topics Underwater diving disorders, Underwater diving hazards, Underwater diving physiology, so understanding it makes those chapters shorter.
In everyday life: Look for High-pressure nervous syndrome outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study High-pressure nervous syndrome in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what High-pressure nervous syndrome means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain High-pressure nervous syndrome out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is High-pressure nervous syndrome in simple terms?

Why does High-pressure nervous syndrome matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study High-pressure nervous syndrome?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on High-pressure nervous syndrome.