Doppler grades

[Kendall Raine]

A friend recently quoted a dive industry professional as saying that a Grade III score following a dive on nitrox would be equivalent to a Grade I score following a dive on heliox. The intuition was that helium dominant bubbles, though potentially more numerous, are generally smaller and of less threat to clinical DCI than a nitrogen dominant bubble. I had not heard of practitioners recalibrating bubble scores depending on constituent inert gas. I thought a K-M Grade III was just that, whether heliox, nitrox or trimix. Furthermore, I recall seeing a table in Bennet and Elliott that indicated a higher probability for DCI from a high heliox score versus a high nitrox score.

Please help.

Kendall

 

[Kendall Raine]

I got it backward. The assertion was a Grade III following a heliox dive would be equivalent (whatever that means) with a Grade I following a nitrox dive. Sorry.

A friend recently quoted a dive industry professional as saying that a Grade III score following a dive on nitrox would be equivalent to a Grade I score following a dive on heliox. The intuition was that helium dominant bubbles, though potentially more numerous, are generally smaller and of less threat to clinical DCI than a nitrogen dominant bubble. I had not heard of practitioners recalibrating bubble scores depending on constituent inert gas. I thought a K-M Grade III was just that, whether heliox, nitrox or trimix. Furthermore, I recall seeing a table in Bennet and Elliott that indicated a higher probability for DCI from a high heliox score versus a high nitrox score.

Please help.

Kendall

 

[Dr Deco]

Hello Kendal:

Doppler Grades:

There are differences in the associated risk of Doppler bubbles depending on the predominant gas. This was first mentioned in Powell (1974) concerning Doppler scores, DCS, and diving gas in experiments with pigs. [see references below]. The explanation given between nitrogen and helium is that nitrogen is more fat soluble. This being true, there will always be a large ”background” of bubbles from adipose tissue. when helium is the diving gas, the bubbles are predominantly from muscle (and some from adipose) tissue. Thus it often be noted that air divers [animals or humans] will have no particular DCS risk if a Spencer-Johanson Grade of II is observed.

I am not aware of any comparison of air, nitrox, and helium relative to Doppler scores and DCS risk.

Dr Deco :doctor:

References

MR Powell. Doppler ultrasound monitoring of venous gas bubbles in pigs following decompression from helium, neon, and air. Aerospace Med., 45, 505-508 (1974).

MR Powell and DC Johanson. Ultrasound Monitoring and Decompression Sickness. In: Proceedings. VI Symposium on Underwater Physiology, Undersea Medical Society, Bethesda (1978).

MR Powell, MP Spencer, and O von Ramm. Ultrasonic Surveillance of Decompression. In: The Physiology and Medicine of Diving, 3rd Edition, [P. Bennett, D. Elliott, eds.] pp. 404-434, Baillière Tindall, London (1982).

 

[Saturation]

Hello Kendall and Dr. Deco:

I just read a post about Kendall's recent dive to 300+ that was used as backdrop for an article about technical diving ... its on SB.

Kendall, if you're at liberty to say, how soon do you notice your precordium bubbles resolve one you start your surface 02? Do you listen and hear a gradual reduction in 'grade'?

Are you at liberty to discuss what schedules you use to 300'?

 

[IndigoBlue]

Gentlemen, if helium is such a great inert gas for scuba, then why do we all not simply always dive HeliOx?

I have never heard of HPNS occurring at tec rec depths, so that should not be the reason why.

 

[Dr Deco]

Helium is an expensive gas compared to compressed air. It is not really all that advantageous for the recreational diver to lay out the additional cost.

Dr D.

 

[Saturation]

To quantify Dr. D's statement, He is about US $.20 cuft if you mix your own gas. Dive shops will sell it for ~ $0.60 a cuft. AL80 with trimix 30/30 would run you between $10-20 a tank. Most recreational dive shops fill air for about $5-10 for an AL80.

 

[chrisch]

Can you explain how this relates to trimix? Does the He dissolve into muscle tissue and the N2 into fat?
As an aside is it worth buying the Bennet and Powell book to read up on this? It is rather expensive.

Best
Chris.

 

[fins wake]

As an aside is it worth buying the Bennet and Powell book to read up on this?

You mean Bennett & Elliott (editors). I like it. The Edmonds, Lowry & Pennefather tome is also very nice. Not cheap either, but also very good and with a slightly different emphasis IMHO.

Do you need works of reference? Well, it helps you sort out e.g. the good points from the less-well-thought-out responses in cyberspace or in some dive courses.

Dr Powell - our very own Dr Deco - has published many peer-reviewed papers (just like his colleagues all over the world) and many of these are referenced in the above-mentioned works of reference. I'm not aware that he's edited or written any specific work of reference himself aimed at the recreational or technical diver, although I hope he finds the time to do so at some point, as he has the great gift of combining easy-to-understand language with highly up-to-date knowledge and some very unique and valuable decompression notions.

In the meantime, I guess you'll have to attend one of his classes or simply follow this forum ...

 

[chrisch]

Bennett & Elliott - yes my mistake - sorry. I have tried to find it here in a lending library (they are free to borrow if you're reading in the market-forces obsessed USA BTW) and have had no luck. The British Library (London) carries a copy of all books with an ISBN number and you can read them (free!!) on-site but cannot borrow (I think). However, it seems a bit big to speed read in a lunchbreak!!

Chris