Heliox

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Heliox
Identifiers
CAS Number
PubChem CID
Chemical and physical data
Formula He.O2
Molar mass 36.001

Heliox is a breathing gas mixture of helium (He) and oxygen (O2). It is used as a medical treatment for patients with difficulty breathing because this mixture generates less resistance than atmospheric air when passing through the airways of the lungs, and thus requires less effort by a patient to breathe in and out of the lungs. It is also used as a breathing gas diluent for deep ambient pressure diving as it is not narcotic at high pressure, and for its low work of breathing.

Contents

Heliox has been used medically since the 1930s, and although the medical community adopted it initially to alleviate symptoms of upper airway obstruction, its range of medical uses has since expanded greatly, mostly because of the low density of the gas. [1] [2] Heliox is also used in saturation diving and sometimes during the deep phase of technical dives. [3] [4] [5]

Medical uses

In medicine, heliox may refer to a mixture of 21% O2 (the same as air) and 79% He, although other combinations are available (70/30 and 60/40).

Heliox generates less airway resistance than air and thereby requires less mechanical energy to ventilate the lungs. [6] "Work of breathing" (WOB) is reduced by two mechanisms:

  1. increased tendency to laminar flow;
  2. reduced resistance in turbulent flow due to lower density.

Heliox 20/80 diffuses 1.8 times faster than oxygen, and the flow of heliox 20/80 from an oxygen flowmeter is 1.8 times the normal flow for oxygen. [7]

Heliox has a similar viscosity to air but a significantly lower density (0.5 g/L versus 1.25 g/L at STP). Flow of gas through the airway comprises laminar flow, transitional flow and turbulent flow. The tendency for each type of flow is described by the Reynolds number. Heliox's low density produces a lower Reynolds number and hence higher probability of laminar flow for any given airway. Laminar flow tends to generate less resistance than turbulent flow.

In the small airways where flow is laminar, resistance is proportional to gas viscosity and is not related to density and so heliox has little effect. The Hagen–Poiseuille equation describes laminar resistance. In the large airways where flow is turbulent, resistance is proportional to density, so heliox has a significant effect.

There is also some use of heliox in conditions of the medium airways (croup, asthma and chronic obstructive pulmonary disease). A recent trial has suggested that lower fractions of helium (below 40%) – thus allowing a higher fraction of oxygen – might also have the same beneficial effect on upper airway obstruction. [8]

Patients with these conditions may develop a range of symptoms including dyspnea (breathlessness), hypoxemia (below-normal oxygen content in the arterial blood) and eventually a weakening of the respiratory muscles due to exhaustion, which can lead to respiratory failure and require intubation and mechanical ventilation. Heliox may reduce all these effects, making it easier for the patient to breathe. [9] Heliox has also found utility in the weaning of patients off mechanical ventilation, and in the nebulization of inhalable drugs, particularly for the elderly. [10] Research has also indicated advantages in using helium–oxygen mixtures in delivery of anaesthesia. [11]

History

Heliox has been used medically since the early 1930s. It was the mainstay of treatment in acute asthma before the advent of bronchodilators. Currently, heliox is mainly used in conditions of large airway narrowing (upper airway obstruction from tumors or foreign bodies and vocal cord dysfunction).

Usage in diving

Gnome-mime-sound-openclipart.svg
Effect of helium on a human voice
The effect of helium on a human voice
Problems playing this file? See media help.

Helium diluted breathing gases are used to eliminate or reduce the effects of inert gas narcosis, and to reduce work of breathing due to increased gas density at depth. From the 1960s saturation diving physiology studies were conducted with helium from 45 to 610 m (148 to 2,001 ft) over several decades by a Hyperbaric Experimental Centre operated by the French company COMEX specializing in engineering and deep diving operations. [12] Owing to the expense of helium, [13] heliox is most likely to be used in deep saturation diving. It is also sometimes used by technical divers, particularly those using rebreathers, which conserve the breathing gas at depth much better than open circuit scuba.

Heliox Diving cylinder coloring Illustration of cylinder shoulder painted in brown and white quarters IMCA Heliox shoulder quartered.svg
Heliox Diving cylinder coloring Illustration of cylinder shoulder painted in brown and white quarters
Illustration of cylinder shoulder painted in brown (lower) and white (upper) bands, Brown and white quarters or bands or Brown and white short (8 inches (20 cm)) alternating bands IMCA Heliox shoulder.svg
Illustration of cylinder shoulder painted in brown (lower) and white (upper) bands, Brown and white
quarters or bands or Brown and white
short (8 inches (20 cm))
alternating bands

The proportion of oxygen in a diving mix depends on the maximum depth of the dive plan, but it is often hypoxic and may be less than 10%. Each mix is custom made using gas blending techniques, which often involve the use of booster pumps to achieve typical diving cylinder pressures of 200 to 300  bar (2,900 to 4,400  psi ) from lower pressure banks of oxygen and helium cylinders.

Because sound travels faster in heliox than in air, voice formants are raised, making divers' speech very high-pitched and hard to understand to people not used to it. [14] Surface personnel often employ a piece of communications equipment called a "helium de-scrambler", which electronically lowers the pitch of the diver's voice as it is relayed through the communications gear, making it easier to understand.

Trimix is a less expensive alternative to heliox for deep diving, which uses only enough helium to limit narcosis and gas density to tolerable levels for the planned depth. [15] Trimix is often used in technical diving, and is also sometimes used in professional diving.

In 2015, the United States Navy Experimental Diving Unit showed that decompression from bounce dives using trimix is not more efficient than dives on heliox. [16]

See also

Related Research Articles

Nitrox refers to any gas mixture composed of nitrogen and oxygen. This includes atmospheric air, which is approximately 78% nitrogen, 21% oxygen, and 1% other gases, primarily argon. In the usual application, underwater diving, nitrox is normally distinguished from air and handled differently. The most common use of nitrox mixtures containing oxygen in higher proportions than atmospheric air is in scuba diving, where the reduced partial pressure of nitrogen is advantageous in reducing nitrogen uptake in the body's tissues, thereby extending the practicable underwater dive time by reducing the decompression requirement, or reducing the risk of decompression sickness.

<span class="mw-page-title-main">Nitrogen narcosis</span> Reversible narcotic effects of respiratory nitrogen at elevated partial pressures

Narcosis while diving is a reversible alteration in consciousness that occurs while diving at depth. It is caused by the anesthetic effect of certain gases at high pressure. The Greek word νάρκωσις (narkōsis), "the act of making numb", is derived from νάρκη (narkē), "numbness, torpor", a term used by Homer and Hippocrates. Narcosis produces a state similar to drunkenness, or nitrous oxide inhalation. It can occur during shallow dives, but does not usually become noticeable at depths less than 30 metres (98 ft).

<span class="mw-page-title-main">Trimix (breathing gas)</span> Breathing gas consisting of oxygen, helium and nitrogen

Trimix is a breathing gas consisting of oxygen, helium and nitrogen and is used in deep commercial diving, during the deep phase of dives carried out using technical diving techniques, and in advanced recreational diving.

<span class="mw-page-title-main">Technical diving</span> Extended scope recreational diving

Technical diving is scuba diving that exceeds the agency-specified limits of recreational diving for non-professional purposes. Technical diving may expose the diver to hazards beyond those normally associated with recreational diving, and to a greater risk of serious injury or death. The risk may be reduced by appropriate skills, knowledge and experience, and by using suitable equipment and procedures. The skills may be developed through appropriate specialised training and experience. The equipment involves breathing gases other than air or standard nitrox mixtures, and multiple gas sources.

<span class="mw-page-title-main">Deep diving</span> Underwater diving to a depth beyond the norm accepted by the associated community

Deep diving is underwater diving to a depth beyond the norm accepted by the associated community. In some cases this is a prescribed limit established by an authority, while in others it is associated with a level of certification or training, and it may vary depending on whether the diving is recreational, technical or commercial. Nitrogen narcosis becomes a hazard below 30 metres (98 ft) and hypoxic breathing gas is required below 60 metres (200 ft) to lessen the risk of oxygen toxicity.

<span class="mw-page-title-main">Breathing gas</span> Gas used for human respiration

A breathing gas is a mixture of gaseous chemical elements and compounds used for respiration. Air is the most common and only natural breathing gas, but other mixtures of gases, or pure oxygen, are also used in breathing equipment and enclosed habitats. Oxygen is the essential component for any breathing gas. Breathing gases for hyperbaric use have been developed to improve on the performance of ordinary air by reducing the risk of decompression sickness, reducing the duration of decompression, reducing nitrogen narcosis or allowing safer deep diving

<span class="mw-page-title-main">Gas blending for scuba diving</span> Mixing and filling cylinders with breathing gases for use when scuba diving

Gas blending for scuba diving is the filling of diving cylinders with non-air breathing gases such as nitrox, trimix and heliox. Use of these gases is generally intended to improve overall safety of the planned dive, by reducing the risk of decompression sickness and/or nitrogen narcosis, and may improve ease of breathing.

High-pressure nervous 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.

Hydreliox is an exotic breathing gas mixture of hydrogen, helium, and oxygen. For the Hydra VIII mission at 50 atmospheres of ambient pressure, the mixture used was 49% hydrogen, 50.2% helium, and 0.8% oxygen.

Argox is the informal name for a scuba diving breathing gas consisting of argon and oxygen. Occasionally the term argonox has been used to mean the same mix. The blend may consist of varying fractions of argon and oxygen, depending on its intended use. The mixture is made with the same gas blending techniques used to make nitrox, except that for argox, the argon is added to the initial pure oxygen partial-fill, instead of air.

In physiology, isobaric counterdiffusion (ICD) is the diffusion of different gases into and out of tissues while under a constant ambient pressure, after a change of gas composition, and the physiological effects of this phenomenon. The term inert gas counterdiffusion is sometimes used as a synonym, but can also be applied to situations where the ambient pressure changes. It has relevance in mixed gas diving and anesthesiology.

Hydrox, a gas mixture of hydrogen and oxygen, is occasionally used as an experimental breathing gas in very deep diving. It allows divers to descend several hundred metres. Hydrox has been used experimentally in surface supplied, saturation, and scuba diving, both on open circuit and with closed circuit rebreathers.

Equivalent narcotic depth (END) (historically also equivalent nitrogen depth) is used in technical diving as a way of estimating the narcotic effect of a breathing gas mixture, such as nitrox, heliox or trimix. The method is used, for a given breathing gas mix and dive depth, to calculate the equivalent depth which would produce about the same narcotic effect when breathing air.

Hydrogen narcosis is the psychotropic state induced by breathing hydrogen at high pressures. Hydrogen narcosis produces symptoms such as hallucinations, disorientation, and confusion, which are similar to hallucinogenic drugs. It can be experienced by deep-sea divers who dive to 300 m (1,000 ft) below sea level breathing hydrogen mixtures. However, hydrogen has far less narcotic effect than nitrogen and is very rarely used in diving. In tests of the effect of hydrogen narcosis, where divers dived to 500 m (1,600 ft) with a hydrogen–helium–oxygen (hydreliox) mixture containing 49% hydrogen, it was found that while the narcotic effect of hydrogen was detectable, the neurological symptoms of high-pressure nervous syndrome were only moderate.

Medical gas therapy is a treatment involving the administration of various gases. It has been used in medicine since the use of oxygen therapy. Many other gases, collectively known as factitious airs, were explored for medicinal value in the late eighteenth century.

<span class="mw-page-title-main">Scuba gas management</span> Logistical aspects of scuba breathing gas

Scuba gas management is the aspect of scuba diving which includes the gas planning, blending, filling, analysing, marking, storage, and transportation of gas cylinders for a dive, the monitoring and switching of breathing gases during a dive, efficient and correct use of the gas, and the provision of emergency gas to another member of the dive team. The primary aim is to ensure that everyone has enough to breathe of a gas suitable for the current depth at all times, and is aware of the gas mixture in use and its effect on decompression obligations, nitrogen narcosis, and oxygen toxicity risk. Some of these functions may be delegated to others, such as the filling of cylinders, or transportation to the dive site, but others are the direct responsibility of the diver using the gas.

Gas blending is the process of mixing gases for a specific purpose where the composition of the resulting mixture is specified and controlled. A wide range of applications include scientific and industrial processes, food production and storage and breathing gases.

Work of breathing (WOB) is the energy expended to inhale and exhale a breathing gas. It is usually expressed as work per unit volume, for example, joules/litre, or as a work rate (power), such as joules/min or equivalent units, as it is not particularly useful without a reference to volume or time. It can be calculated in terms of the pulmonary pressure multiplied by the change in pulmonary volume, or in terms of the oxygen consumption attributable to breathing.

Human physiology of underwater diving is the physiological influences of the underwater environment on the human diver, and adaptations to operating underwater, both during breath-hold dives and while breathing at ambient pressure from a suitable breathing gas supply. It, therefore, includes the range of physiological effects generally limited to human ambient pressure divers either freediving or using underwater breathing apparatus. Several factors influence the diver, including immersion, exposure to the water, the limitations of breath-hold endurance, variations in ambient pressure, the effects of breathing gases at raised ambient pressure, effects caused by the use of breathing apparatus, and sensory impairment. All of these may affect diver performance and safety.

References

  1. ↑ Barach AL, Eckman M (January 1936). "The effects of inhalation of helium mixed with oxygen on the mechanics of respiration". The Journal of Clinical Investigation. 15 (1): 47–61. doi:10.1172/JCI100758. PMC   424760 . PMID   16694380.
  2. ↑ "Heliox product information". BOC Medical. Archived from the original on 21 November 2008.
  3. ↑ US Navy Diving Manual, 6th revision. United States: US Naval Sea Systems Command. 2008. Archived from the original on 2008-05-02. Retrieved 2008-07-08.
  4. ↑ Brubakk AO, Neuman TS (2003). Bennett and Elliott's physiology and medicine of diving (5th Rev ed.). United States: Saunders Ltd. p. 800. ISBN   0-7020-2571-2.
  5. ↑ "COMEX PRO".
  6. ↑ "Heliox21". Linde Gas Therapeutics. 27 January 2009. Retrieved 13 April 2011.
  7. ↑ Hess DR, Fink JB, Venkataraman ST, Kim IK, Myers TR, Tano BD (June 2006). "The history and physics of heliox" (PDF). Respiratory Care. 51 (6): 608–612. PMID   16723037. Archived (PDF) from the original on 2022-10-09.
  8. ↑ Truebel H, Wuester S, Boehme P, Doll H, Schmiedl S, Szymanski J, et al. (May 2019). "A proof-of-concept trial of HELIOX with different fractions of helium in a human study modeling upper airway obstruction". European Journal of Applied Physiology. 119 (5): 1253–1260. doi:10.1007/s00421-019-04116-7. PMID   30850876. S2CID   71715570.
  9. ↑ BOC Medical. "Heliox data sheet" (PDF). Archived (PDF) from the original on 2022-10-09.
  10. ↑ Lee DL, Hsu CW, Lee H, Chang HW, Huang YC (September 2005). "Beneficial effects of albuterol therapy driven by heliox versus by oxygen in severe asthma exacerbation". Academic Emergency Medicine. 12 (9): 820–827. doi: 10.1197/j.aem.2005.04.020 . PMID   16141015.
  11. ↑ Buczkowski PW, Fombon FN, Russell WC, Thompson JP (November 2005). "Effects of helium on high frequency jet ventilation in model of airway stenosis". British Journal of Anaesthesia. 95 (5): 701–705. doi: 10.1093/bja/aei229 . PMID   16143576.
  12. ↑ "Extreme Environment Engineering Departement Hyperbaric Experimental Centre - History". Archived from the original on October 5, 2008. Retrieved 2009-02-22.
  13. ↑ "Example pricing for filling cylinders". Archived from the original on 2008-01-16. Retrieved 2008-01-10.
  14. ↑ Ackerman MJ, Maitland G (December 1975). "Calculation of the relative speed of sound in a gas mixture". Undersea Biomedical Research. 2 (4): 305–310. PMID   1226588. Archived from the original on 2011-01-27. Retrieved 2008-07-08.{{cite journal}}: CS1 maint: unfit URL (link)
  15. ↑ Stone WC (1992). "The case for heliox: a matter of narcosis and economics". AquaCorps. 3 (1): 11–16.
  16. ↑ Doolette DJ, Gault KA, Gerth WA (2015). "Decompression from He-N2-O2 (trimix) bounce dives is not more efficient than from He-O2 (heliox) bounce dives". US Navy Experimental Diving Unit Technical Report 15-4. Archived from the original on 2017-07-07. Retrieved 2015-12-30.{{cite journal}}: CS1 maint: unfit URL (link)

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