Talk:Isobaric counterdiffusion

ICD Prevention

"Gas switches that involve going from helium rich mixtures to nitrogen rich mixtures are acceptable ..." is perhaps too strong a statement?

The theory goes like this: If the rate of diffusion is the only factor, then that would hold in all cases. However, nitrogen has a greater solubility than helium. If you do a gas switch at the start of a deco stop, which happens to be close to the inert gas ceiling, then during the stop you may increase the total inert gas loading because of nitrogen's greater solubility. This gives a chance of a fast-tissue hit.

I'm not sure if I've explained that clearly, but there's an article here that discusses ICD in "Type III DCS" and gives some credible math. Sadly it gives no references. BTW. the CSS on that page is screwed in FF3, so best to view it in IE.

See what you think --RexxS (talk) 16:28, 25 June 2008 (UTC)

The statement is from Lambertsen et. al. and pretty strong for their time as well. Unfortunately there has been very little work on this area. Know of any other resource that offers more than more theory? I have been unable to locate anything in my brief searches. --Gene Hobbs (talk) 17:22, 25 June 2008 (UTC)

The ref you gave from Doolette and Mitchell about IEDCS starts its abstract with "Isolated inner ear decompression sickness (DCS) is recognized in deep diving involving breathing of helium-oxygen mixtures, particularly when breathing gas is switched to a nitrogen-rich mixture during decompression." - that's surely an ICD hit contradicting Lambertsen's assertion? I also came across Mark Ellyat's essay on ICD which warns against switching from He to N2 mixes too rapidly and anecdotally mentions continuous vomiting as a likely outcome. That sounds like he considers IEDCS the result of a bad switch causing an ICD hit. It might take some work to find good research to back all this up, but it leaves me with the feeling that Lambertsen hadn't got hold of the whole picture. Trawling through the tech diving forums will show the concern tech divers have with the He->N2 switch, but again that's not exactly WP:RS. I'll keep looking! --RexxS (talk) 21:59, 25 June 2008 (UTC)

There is actually quite a few case reports of switching from heliox saturation to nitrogen based gas mixes (usually air in the early 80's). Most of these were either inner ear or skin hits. David and Simon's paper is one of the best ever looking at a specific organ system and is a great PRIMARY source for this (In Ellyatt's work, vomiting is a sign of the vestibular hit). My main concern is keeping the historical context while updating to more current understanding. As usual, I defer to you for "how" to word the entry better. Thanks for catching this. --Gene Hobbs (talk) 01:16, 26 June 2008 (UTC)

I finally remembered I wanted to qualify Lambertsen's comment! The Doolette & Mitchell analysis is pretty compelling and already referenced, so I used that and added on Steve Burton's thoughts about relative solubilities as an extra. I know the latter isn't very WP:RS, but the math makes sense, even if the physiology is simplistic, so I'd guess it could stand on its own strength as a source. By the way, the Doolette & Mitchell ref contained its own reference to "3. Farmer, JC, Thomas WG, Youngblood DG, and Bennett PB. Inner ear decompression sickness. Laryngoscope 86: 1315-1327, 1976." which is described at one point as "the series ... (of cases)", so that may be a relatively early collection of data on IEDCS. Sadly, I don't have access to Laryngoscope. Have you got sight of it, Gene? It would be fascinating to see what they had found as early as 1976. --RexxS (talk) 22:42, 18 September 2008 (UTC)

That's perfect! I do have access (especially since it is work from my lab) and will try to get over to the library tomorrow for you. Joe's office is also downstairs so I might be able to get it from his collection and save the longer walk. Joe also holds the ENT chapter in The Physiology and Medicine of Diving and Compressed Air Work so you might find a little more there in the mean time. Thanks again for updating this! --Gene Hobbs (talk) 23:26, 18 September 2008 (UTC)

Ambient pressure

The ambient link goes to a disambiguation page but as the DAB page doesn't contain "ambient pressure", the guideline is to remove the link in this article :(

Amazingly, there was no article on "ambient pressure" on Wikipedia, Wikiversity or Wiktionary. Yet I'm certain that the phrase needs qualification or definition for the general reader. So I went ahead and created Ambient pressure as a definition. However, when checking for a stub type to use on it, I came to the conclusion that it should be in Wiktionary and included a "Copy to Wiktionary" template. Hopefully that will create a usable entry there, but the link here will probably need to be redirected.

Just in case this all goes wrong, I've copied my definition here to re-use in some way later:

The '''ambient pressure''' on an object is the pressure of the surrounding medium, such as a gas or liquid, which comes into contact with the object.<ref>{{cite web |url=http://www.answers.com/topic/ambient-pressure |title=Sci-Tech Dictionary ambient pressure on Answers.com |author=McGraw-Hill Dictionary of Scientific and Technical Terms Copyright © 2003 by McGraw-Hill Companies, Inc. |publisher=McGraw-Hill Companies, Inc.}}</ref>

--RexxS (talk) 22:44, 2 August 2008 (UTC)

That's probably not going to work :( - since "ambient" means "surrounding", ambient pressure means surrounding pressure and I think that's simple enough for Wiktionary not to consider it idiomatic. So from what I've read, it doesn't merit inclusion as a compound (Wiktionary has a fried egg test!!). Nevertheless, I think we can get round the problem of the dab-page for Ambient not including pressure. Use instead: "[[wikt:ambient|ambient]] pressure" which renders as ambient pressure. Anyone not certain about the term then gets a dictionary definition of ambient which should be sufficient to clarify. --RexxS (talk) 23:45, 18 September 2008 (UTC)

Definition and scope

Current definition:

Isobaric counterdiffusion, inert gas counterdiffusion (ICD) is the physiological effect of diffusion of different gases occurring in opposite directions while under a constant ambient pressure.

However this appears to be a definition of isobaric counterdiffusion by itself:

diffusion (of different gases) occurring in opposite directions = counterdiffusion, while under a constant ambient pressure = isobaric

Why the specification of physiological effect for what appears to be an adequate physical description, which can occur inside or outside of a physiological environment? I get that the physiological aspects of the phenomenon are the main subject of the article at present, but would that not suggest either a different title, or that the current article should be expanded to cover the full scope of the physical phenomenon, and the definition changed? Furthermore, the content is restricted to diffusion of gases, which is not implied by the logical meaning of the term. Everything in the article centres on the physiological meaning of ICD, so maybe the title should be amended to limit the scope to what the article is actually and intended to be about. I suggest changing the article name to Isobaric counterdiffucion (physiology), and the lead statement to:

In physiology, isobaric counterdiffusion (ICD) is the diffusion in opposite directions of different gases through tissues while under a constant ambient pressure, and the physiological effects of this phenomenon.

Inert gas counterdiffusion could occur during changes in ambient pressure. It is not identical in meaning to isobaric counterdiffusion, even if the two terms are often used as if they mean the same thing. • • • Peter (Southwood) ^(talk): 10:54, 17 March 2016 (UTC)

I agree that "inert gas counterdiffusion" is a poor description of the effect, and I can happily claim I've never used it. I do accept that "isobaric counterdiffusion" could cover the general physical action of two different gasses diffusing in opposite directions, but in itself, it's not a particularly interesting phenomenon. So much so that I don't think that it is notable enough to sustain a article. It's only when you consider the physiological effects - particularly in a diving environment - that you start to get notability. A Google search on "isobaric counterdiffusion" gives 3,680 ghits and every one that I've looked at is concerned with diving. Google Scholar gives 123 results - all diving-related, apart from the odd experiment on rabbits. PubMed only has 6 results, and the only one that looks like it's not related to DCS is Kinetics of isobaric counterdiffusion 1977, PMID 196707 - but the co-author is Christian Lambertsen!

So the point I want to make is that there is not really much in the way of sources to make an article about the physical action of isobaric counterdiffusion. In which case we don't need any disambiguation (i.e. the term in parentheses) and the physiological effect would be the primary topic anyway. As I understand it, per WP:PRECISION calling this article Isobaric counterdiffusion is fine. Cheers --RexxS (talk) 02:10, 18 March 2016 (UTC)

OK, we can keep the name, but I will tweak the lead a bit.• • • Peter (Southwood) ^(talk): 10:29, 18 March 2016 (UTC)

That's a definite improvement. Thanks, Peter. --RexxS (talk) 14:02, 18 March 2016 (UTC)