Isobaric counterdiffusion

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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. [1] [2] It has relevance in mixed gas diving and anesthesiology.[ citation needed ]

Contents

Background

Isobaric counterdiffusion was first described by Graves, Idicula, Lambertsen, and Quinn in 1973 in subjects who breathed one gas mixture (in which the inert component was nitrogen or neon) while being surrounded by another (helium based). [3] [4]

Clinical relevance

In medicine, ICD is the diffusion of gases in different directions that can increase the pressure inside open air spaces of the body and surrounding equipment. [5]

An example of this would be a patient breathing nitrous oxide in an operating room (surrounded by air). Cuffs on the endotracheal tubes must be monitored as nitrous oxide will diffuse into the air filled space causing the volume to increase. In laparoscopic surgery, nitrous oxide is avoided since the gas will diffuse into the abdominal or pelvic cavities causing an increase in internal pressure. In the case of a tympanoplasty, the skin flap will not lay down as the nitrous oxide will be diffusing into the middle ear.[ citation needed ]

Relevance to diving

In underwater diving, ICD is the diffusion of one inert gas into body tissues while another inert gas is diffusing out. While not strictly speaking a phenomenon of decompression, it is a complication that can occur during decompression, and that can result in the formation or growth of bubbles without changes in the environmental pressure. [6] [7] If the gas that is diffusing into a tissue does so at a rate which exceeds the rate of the other leaving the tissue, it can raise the combined gas concentration in the tissue to a supersaturation sufficient to cause the formation or growth of bubbles, without changes in the environmental pressure, and in particular, without concurrent decompression. Two forms of this phenomenon have been described by Lambertsen: [1] [8]

Superficial ICD

Superficial ICD (also known as Steady State Isobaric Counterdiffusion) occurs when the inert gas breathed by the diver diffuses more slowly into the body than the inert gas surrounding the body. [1] [8] [9]

An example of this would be breathing air in a heliox environment. The helium in the heliox diffuses into the skin quickly, while the nitrogen diffuses more slowly from the capillaries to the skin and out of the body. The resulting effect generates supersaturation in certain sites of the superficial tissues and the formation of inert gas bubbles. These isobaric skin lesions (urticaria) do not occur when the ambient gas is nitrogen and the breathing gas is helium. [10] [9]

Deep tissue ICD

Deep tissue ICD (also known as Transient Isobaric Counterdiffusion) occurs when different inert gases are breathed by the diver in sequence. [1] [8] The rapidly diffusing gas is transported into the tissue faster than the slower diffusing gas is transported out of the tissue. [7]

An example of this was shown in the literature by Harvey in 1977 as divers switched from a nitrogen mixture to a helium mixture (diffusivity of helium is 2.65 times faster than nitrogen), [7] they quickly developed itching followed by joint pain. [11] Saturation divers breathing hydreliox switched to a heliox mixture and developed symptoms of decompression sickness during Hydra V. [12] In 2003 Doolette and Mitchell described ICD as the basis for inner ear decompression sickness and suggest "breathing-gas switches should be scheduled deep or shallow to avoid the period of maximum supersaturation resulting from decompression". [13] It can also happen when saturation divers breathing hydreliox switch to a heliox mixture. [14]

There is another effect which can manifest as a result of the disparity in solubility between inert breathing gas diluents, which occurs in isobaric gas switches near the decompression ceiling between a low solubility gas (typically helium, and a higher solubility gas, typically nitrogen) [15] [16]

An inner ear decompression model by Doolette and Mitchell suggests that a transient increase in gas tension after a switch from helium to nitrogen in breathing gas may result from the difference in gas transfer between compartments. If the transport of nitrogen into the vascular compartment by perfusion exceeds removal of helium by perfusion, while transfer of helium into the vascular compartment by diffusion from the perilymph and endolymph exceeds the counterdiffusion of nitrogen, this may result in a temporary increase in total gas tension, as the input of nitrogen exceeds the removal of helium, which can result in bubble formation and growth. This model suggests that diffusion of gases from the middle ear across the round window is negligible. The model is not necessarily applicable to all tissue types. [13]

ICD prevention

Lambertsen made suggestions to help avoid ICD while diving. [1] [8] If the diver is surrounded by or saturated with nitrogen, they should not breathe helium rich gases. Lambertson also proposed that gas switches that involve going from helium rich mixtures to nitrogen rich mixtures would be acceptable, but changes from nitrogen to helium should include recompression. However Doolette and Mitchell's more recent study of inner ear decompression sickness (IEDCS) now shows that the inner ear may not be well-modelled by common (e.g. Bühlmann) algorithms. Doolette and Mitchell propose that a switch from a helium-rich mix to a nitrogen-rich mix, as is common in technical diving when switching from trimix to nitrox on ascent, may cause a transient supersaturation of inert gas within the inner ear and result in IEDCS. [13] A similar hypothesis to explain the incidence of IEDCS when switching from trimix to nitrox was proposed by Steve Burton, who considered the effect of the much greater solubility of nitrogen than helium in producing transient increases in total inert gas pressure, which could lead to DCS under isobaric conditions. [17] Recompression with oxygen is effective for relief of symptoms resulting from ICD. However, Burton's model for IEDCS does not agree with Doolette and Mitchell's model of the inner ear. Doolette and Mitchell model the inner ear using solubility coefficients close to that of water. [13] They suggest that breathing-gas switches from helium-rich to nitrogen-rich mixtures should be carefully scheduled either deep (with due consideration to nitrogen narcosis) or shallow to avoid the period of maximum supersaturation resulting from the decompression. Switches should also be made during breathing of the largest inspired oxygen partial pressure that can be safely tolerated with due consideration to oxygen toxicity. [13]

A similar hypothesis to explain the incidence of IEDCS when switching from trimix to nitrox was proposed by Steve Burton, who considered the effect of the much greater solubility of nitrogen than helium in producing transient increases in total inert gas pressure, which could lead to DCS under isobaric conditions. [18]

Burton argues that effect of switching to Nitrox from Trimix with a large increase of nitrogen fraction at constant pressure has the effect of increasing the overall gas loading within particularly the faster tissues, since the loss of helium is more than compensated by the increase in nitrogen. This could cause immediate bubble formation and growth in the fast tissues. A simple rule for avoidance of ICD when gas switching at a decompression ceiling is suggested: [18]

This rule has been found to successfully avoid ICD on hundreds of deep trimix dives. [18]

A decompression planning software tool called Ultimate Planner attempts to predict ICD through modeling the inner ear as either aqueous (Mitchell and Doolette's approach) or lipid tissue (Burton's approach). [19]

See also

Related Research Articles

<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 partial 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.

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.

<span class="mw-page-title-main">Decompression sickness</span> Disorder caused by dissolved gases forming bubbles in tissues

Decompression sickness is a medical condition caused by dissolved gases emerging from solution as bubbles inside the body tissues during decompression. DCS most commonly occurs during or soon after a decompression ascent from underwater diving, but can also result from other causes of depressurisation, such as emerging from a caisson, decompression from saturation, flying in an unpressurised aircraft at high altitude, and extravehicular activity from spacecraft. DCS and arterial gas embolism are collectively referred to as decompression illness.

<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.

The Varying Permeability Model, Variable Permeability Model or VPM is an algorithm that is used to calculate the decompression stops needed for ambient pressure dive profiles using specified breathing gases. It was developed by D.E. Yount and others for use in professional diving and recreational diving. It was developed to model laboratory observations of bubble formation and growth in both inanimate and in vivo systems exposed to pressure. In 1986, this model was applied by researchers at the University of Hawaii to calculate diving decompression tables.

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.

The Bühlmann decompression model is a neo-Haldanian model which uses Haldane's or Schreiner's formula for inert gas uptake, a linear expression for tolerated inert gas pressure coupled with a simple parameterised expression for alveolar inert gas pressure and expressions for combining Nitrogen and Helium parameters to model the way inert gases enter and leave the human body as the ambient pressure and inspired gas changes. Different parameter sets are used to create decompression tables and in personal dive computers to compute no-decompression limits and decompression schedules for dives in real-time, allowing divers to plan the depth and duration for dives and the required decompression stops.

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.

<span class="mw-page-title-main">Decompression (diving)</span> Pressure reduction and its effects during ascent from depth

The decompression of a diver is the reduction in ambient pressure experienced during ascent from depth. It is also the process of elimination of dissolved inert gases from the diver's body which accumulate during ascent, largely during pauses in the ascent known as decompression stops, and after surfacing, until the gas concentrations reach equilibrium. Divers breathing gas at ambient pressure need to ascend at a rate determined by their exposure to pressure and the breathing gas in use. A diver who only breathes gas at atmospheric pressure when free-diving or snorkelling will not usually need to decompress. Divers using an atmospheric diving suit do not need to decompress as they are never exposed to high ambient pressure.

<span class="mw-page-title-main">Decompression practice</span> Techniques and procedures for safe decompression of divers

To prevent or minimize decompression sickness, divers must properly plan and monitor decompression. Divers follow a decompression model to safely allow the release of excess inert gases dissolved in their body tissues, which accommodated as a result of breathing at ambient pressures greater than surface atmospheric pressure. Decompression models take into account variables such as depth and time of dive, breathing gasses, altitude, and equipment to develop appropriate procedures for safe ascent.

<span class="mw-page-title-main">History of decompression research and development</span> Chronological list of notable events in the history of diving decompression.

Decompression in the context of diving derives from the reduction in ambient pressure experienced by the diver during the ascent at the end of a dive or hyperbaric exposure and refers to both the reduction in pressure and the process of allowing dissolved inert gases to be eliminated from the tissues during this reduction in pressure.

<span class="mw-page-title-main">Decompression theory</span> Theoretical modelling of decompression physiology

Decompression theory is the study and modelling of the transfer of the inert gas component of breathing gases from the gas in the lungs to the tissues and back during exposure to variations in ambient pressure. In the case of underwater diving and compressed air work, this mostly involves ambient pressures greater than the local surface pressure, but astronauts, high altitude mountaineers, and travellers in aircraft which are not pressurised to sea level pressure, are generally exposed to ambient pressures less than standard sea level atmospheric pressure. In all cases, the symptoms caused by decompression occur during or within a relatively short period of hours, or occasionally days, after a significant pressure reduction.

Brian Andrew Hills, born 19 March 1934 in Cardiff, Wales, died 13 January 2006 in Brisbane, Queensland, was a physiologist who worked on decompression theory.

<span class="mw-page-title-main">Thermodynamic model of decompression</span> Early model in which decompression is controlled by volume of gas bubbles forming in tissues

The thermodynamic model was one of the first decompression models in which decompression is controlled by the volume of gas bubbles coming out of solution. In this model, pain only DCS is modelled by a single tissue which is diffusion-limited for gas uptake and bubble-formation during decompression causes "phase equilibration" of partial pressures between dissolved and free gases. The driving mechanism for gas elimination in this tissue is inherent unsaturation, also called partial pressure vacancy or the oxygen window, where oxygen metabolised is replaced by more soluble carbon dioxide. This model was used to explain the effectiveness of the Torres Straits Island pearl divers empirically developed decompression schedules, which used deeper decompression stops and less overall decompression time than the current naval decompression schedules. This trend to deeper decompression stops has become a feature of more recent decompression models.

<span class="mw-page-title-main">Physiology of decompression</span> The physiological basis for decompression theory and practice

The physiology of decompression is the aspect of physiology which is affected by exposure to large changes in ambient pressure. It involves a complex interaction of gas solubility, partial pressures and concentration gradients, diffusion, bulk transport and bubble mechanics in living tissues. Gas is breathed at ambient pressure, and some of this gas dissolves into the blood and other fluids. Inert gas continues to be taken up until the gas dissolved in the tissues is in a state of equilibrium with the gas in the lungs, or the ambient pressure is reduced until the inert gases dissolved in the tissues are at a higher concentration than the equilibrium state, and start diffusing out again.

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.

Inner ear decompression sickness, (IEDCS) or audiovestibular decompression sickness is a medical condition of the inner ear caused by the formation of gas bubbles in the tissues or blood vessels of the inner ear. Generally referred to as a form of decompression sickness, it can also occur at constant pressure due to inert gas counterdiffusion effects.

References

  1. 1 2 3 4 5 Hamilton, Robert W; Thalmann, Edward D (2003). "Decompression Practice". In Brubakk, Alf O; Neuman, Tom S (eds.). Bennett and Elliott's physiology and medicine of diving (5th ed.). United States: Saunders. pp. 477–8. ISBN   978-0-7020-2571-6. OCLC   51607923.
  2. ↑ Lambertson, Christian J; Bornmann, Robert C; Kent, MB, eds. (1979). Isobaric Inert Gas Counterdiffusion. 22nd Undersea and Hyperbaric Medical Society Workshop. Vol. UHMS Publication Number 54WS(IC)1-11-82. Archived from the original on August 20, 2008. Retrieved 10 January 2010.{{cite conference}}: CS1 maint: unfit URL (link)
  3. ↑ Graves, DJ; Idicula, J; Lambertsen, Christian J; Quinn, JA (February 1973). "Bubble formation in physical and biological systems: a manifestation of counterdiffusion in composite media". Science. 179 (4073): 582–584. Bibcode:1973Sci...179..582G. doi:10.1126/science.179.4073.582. PMID   4686464. S2CID   46428717.
  4. ↑ Graves, DJ; Idicula, J; Lambertsen, Christian J; Quinn, JA (March 1973). "Bubble formation resulting from counterdiffusion supersaturation: a possible explanation for isobaric inert gas 'urticaria' and vertigo". Physics in Medicine and Biology. 18 (2): 256–264. Bibcode:1973PMB....18..256G. CiteSeerX   10.1.1.555.429 . doi:10.1088/0031-9155/18/2/009. PMID   4805115. S2CID   250737144 . Retrieved 10 January 2010.
  5. ↑ Barash, PG; Cullen, BF; Stoelting, RK (2005). Clinical Anesthesia (5th Rev ed.). United States: Lippincott Williams & Wilkins. ISBN   978-0-7817-5745-4.
  6. ↑ Hamilton & Thalmann 2003, pp. 477–478.
  7. 1 2 3 Lambertson, Christian J (1989). Relations of isobaric gas counterdiffusion and decompression gas lesion diseases. In Vann, RD. "The Physiological Basis of Decompression". 38th Undersea and Hyperbaric Medical Society Workshop UHMS Publication Number 75(Phys)6-1-89. http://archive.rubicon-foundation.org/6853 Archived 2010-01-05 at the Wayback Machine . Retrieved 10 January 2010.
  8. 1 2 3 4 Lambertson, Christian J (1989). "Relations of isobaric gas counterdiffusion and decompression gas lesion diseases". In Vann, RD (ed.). The Physiological Basis of Decompression. 38th Undersea and Hyperbaric Medical Society Workshop. Vol. UHMS Publication Number 75(Phys)6-1-89. Archived from the original on 5 January 2010. Retrieved 10 January 2010.
  9. 1 2 D'Aoust, BG; White, R; Swanson, H; Dunford, RG; Mahoney, J (1982). "Differences in Transient and Steady State Isobaric Counterdiffusion". Report to the Office of Naval Research. Archived from the original on April 15, 2013. Retrieved 10 January 2010.{{cite journal}}: CS1 maint: unfit URL (link)
  10. ↑ Hills, Brian A. (1979). Kent, MB (ed.). "Counter transport of inert gases: Effects of steady state and transient gradients". Isobaric Inert Gas Counterdiffusion. 22nd workshop, Chairs: Lambertsen, CJ; Bornmann, RC. Philadelphia, Pennsylvania.: Undersea Medical Society. p. 151. Archived from the original on August 20, 2008. Retrieved 18 March 2016.{{cite web}}: CS1 maint: unfit URL (link)
  11. ↑ Harvey, CA (1977). "Shallow saturation hyperbaric exposures to nitrogen-oxygen environments and isobaric switches to helium oxygen". Undersea Biomedical Research, Annual Meeting Abstract. Archived from the original on April 16, 2013. Retrieved 10 January 2010.{{cite journal}}: CS1 maint: unfit URL (link)
  12. ↑ Rostain, JC; Lemaire, C; Gardette-Chauffour, MC; Naquet, R (1987). Bove; Bachrach; Greenbaum (eds.). "Effect of the shift from hydrogen-helium-oxygen mixture to helium oxygen mixture during a 450 msw dive". Underwater and Hyperbaric Physiology IX. Bethesda, MD, USA: Undersea and Hyperbaric Medical Society.
  13. 1 2 3 4 5 Doolette, David J; Mitchell, Simon J (June 2003). "Biophysical basis for inner ear decompression sickness". Journal of Applied Physiology. 94 (6): 2145–50. doi:10.1152/japplphysiol.01090.2002. PMID   12562679.
  14. ↑ Masurel, G; Gutierrez, N; Giacomoni, L (1987). "Hydrogen dive and decompression". Abstract of the Undersea and Hyperbaric Medical Society, Inc. Annual Scientific Meeting held May 26–30, 1987. The Hyatt Regency Hotel, Baltimore, Maryland. Undersea and Hyperbaric Medical Society, Inc. Archived from the original on June 2, 2016. Retrieved 14 March 2016.{{cite web}}: CS1 maint: unfit URL (link)
  15. ↑ Partridge, Matthew. "Isobaric Inert Gas Counter diffusion" (PDF). Archived from the original (PDF) on 15 March 2016. Retrieved 14 March 2016.
  16. ↑ Burton, Steve (2011). "Isobaric Counter Diffusion How to avoid a Isobaric Counter Diffusion hit". ScubaEngineer.com. Retrieved 14 March 2016.
  17. ↑ Burton, Steve (December 2004). "Isobaric Counter Diffusion". ScubaEngineer. Retrieved 10 January 2010.
  18. 1 2 3 4 Burton, Steve (December 2004). "Isobaric Counter Diffusion". ScubaEngineer. http://www.scubaengineer.com/isobaric_counter_diffusion.htm. Retrieved 10 January 2010.
  19. ↑ Salama, Asser (2014). "Ultimate planner (deco software)". Tech Diving Mag. Asser Salama. Retrieved 17 March 2016.


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