Isobaric counterdiffusion

: "This article refers to ICD as it relates to tissue diffusion. For other uses of the term ICD, see ICD (disambiguation)"Isobaric Counterdiffusion, Inert Gas Counterdiffusion , or ICD is the term used to describe the physiologic effect when the diffusion of gases occurs opposite each other while maintaining a constant ambient pressure.cite book |title=Bennett and Elliott's physiology and medicine of diving, 5th Rev ed. |last=Brubakk |first=A. O. |coauthors=T. S. Neuman |year=2003 |publisher=Saunders Ltd. |location=United States |isbn=0702025712 |pages=800 ] cite journal |author=Lambertson CJ, Bernmann RC, Kent MB (eds). |title=Isobaric Inert Gas Counterdiffusion |journal=22nd Undersea and Hyperbaric Medical Society Workshop. |volume=UHMS Publication Number 54WS(IC)1-11-82. |date=1979 |pages=182 |url=http://archive.rubicon-foundation.org/4337 |accessdate=2008-05-31 ]

Background

Isobaric Counterdiffusion was first described by Graves, Idicula, Lambertsen, and Quinn. in 1973 in subjects who breathed one inert gas mixture (nitrogen or neon) while being surrounded by another (helium).cite journal |author=Graves DJ, Idicula J, Lambertsen CJ, Quinn JA |title=Bubble formation in physical and biological systems: a manifestation of counterdiffusion in composite media |journal=Science (journal) |volume=179 |issue=73 |pages=582–4 |year=1973 |month=February |pmid=4686464 |doi= |url=http://www.sciencemag.org/cgi/pmidlookup?view=long&pmid=4686464 |accessdate=2008-05-31] cite journal |author=Graves DJ, Idicula J, Lambertsen CJ, Quinn JA |title=Bubble formation resulting from counterdiffusion supersaturation: a possible explanation for isobaric inert gas 'urticaria' and vertigo |journal=Phys Med Biol |volume=18 |issue=2 |pages=256–64 |year=1973 |month=March |pmid=4805115 |doi= |url=http://stacks.iop.org/0031-9155/18/256 |accessdate=2008-05-31]

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. [cite book |title=Clinical Anesthesia, 5th Rev ed. |last=Barash |first=PG |coauthors=Cullen BF and Stoelting RK |year=2005 |publisher=Lippincott Williams & Wilkins. |location=United States |isbn=0781757452 |pages=1584 ]

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.

Diving Relevance

In diving, ICD is the diffusion of gases in different directions that can produce the formation of bubbles without decompression, without changes in the environmental pressure. Two forms of this phenomenon have been described by Lambertsencite journal |author=Vann RD (ed). |title=The Physiological Basis of Decompression |journal=38th Undersea and Hyperbaric Medical Society Workshop. |volume=UHMS Publication Number 75(Phys)6-1-89. |date=1989 |pages=437 |url=http://archive.rubicon-foundation.org/6853 |accessdate=2008-05-31 ] :

Superficial ICD

Superficial ICD occurs when the inert gas breathed by the diver diffuses more slowly into the body than the inert gas surrounding the body. [cite journal |author=D'Aoust BG, White R, Swanson H, Dunford RG, Mahoney J |title=Differences in Transient and Steady State Isobaric Counterdiffusion. |journal=Report to the Office of Naval Research |date=1982 |url=http://archive.rubicon-foundation.org/4629 |accessdate=2008-05-31 ]

An example of this would be breathing air in an 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.

Deep Tissue ICD

Deep Tissue ICD occurs when different inert gases are breathed by the diver in sequence. The rapidly diffusing gas is transported into the tissue faster than the slower diffusing gas is transported out of the tissue.

An example of this was shown in the literature by Harvey in 1977 as divers switched from a nitrogen mixture to a helium mixture they quickly developed itching followed by joint pain. [cite journal |author=Harvey CA |title=SHALLOW SATURATION HYPERBARIC EXPOSURES TO NITROGEN-OXYGEN ENVIRONMENTS AND ISOBARIC SWITCHES TO HELIUM-OXYGEN |journal=Undersea Biomed Res., Annual Meeting Abstract |date=1977 |url=http://archive.rubicon-foundation.org/4201 |accessdate=2008-05-31 ] Saturation divers breathing hydreliox switched to a heliox mixture and developed symptoms of decompression sickness during Hydra V. [cite journal |author=Rostain JC, Lemaire C, Gardette-Chauffour MC, Naquet R |title=Effect of the shift from hydrogen-helium-oxygen mixture to helium oxygen mixture during a 450 msw dive. |journal=In: Bove, Bachrach, Greenbaum (eds.) Underwater and hyperbaric physiology IX. |publisher=Undersea and Hyperbaric Medical Society |location=Bethesda, MD, USA |date=1987 ] More recently, Doolette and Mitchell have 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".cite journal |author=Doolette DJ, Mitchell SJ |title=Biophysical basis for inner ear decompression sickness |journal=J. Appl. Physiol. |volume=94 |issue=6 |pages=2145–50 |year=2003 |month=June |pmid=12562679 |doi=10.1152/japplphysiol.01090.2002 |url=http://jap.physiology.org/cgi/pmidlookup?view=long&pmid=12562679 |accessdate=2008-06-05]

ICD Prevention

Lambertsen made suggestions to help avoid ICD while diving. If the diver is surrounded by or saturated with nitrogen, they should not breath 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. Buhlmann) 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. Another hypothesis to explain the incidence of IEDCS when switching from trimix to nitrox was proposed by Steve Burton, who considered the the effect of the much greater solubility of nitrogen than helium in producing transient increases in total inert gas pressure, which could also lead to DCS under isobaric conditions. [cite web |last=Burton |first=Steve |title=Isobaric Counter Diffusion |publisher=ScubaEngineer |date=December 2004 |url=http://www.scubaengineer.com/isobaric_counter_diffusion.htm |accessdate=2008-09-18] Recompression with oxygen is effective for relief of symptoms resulting from ICD.

References

External resources

[http://www.uphs.upenn.edu/ebdc/components/component_1/primary/10.shtml Lambertsen/ U Penn isobaric counterdiffusion references]