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Mark Milburn
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Discussion Starter · #1 ·
I hate to admit going to the forbidden forum, but just nicked this off there as I thought it was important for any deco diver.

If you don't want to read it all just read the conclusion.
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EMPIRICAL EVALUATION OF THE EFFICACY OF DEEP STOPS IN AIR DECOMPRESSION DIVES



Gerth WA, Gault KA, Doolette DJ



Navy Experimental Diving Unit, Panama City, FL



BACKGROUND: Classical decompression algorithms limit hypothetical tissue gas contents and prescribe decompressions that advance rapidly to shallow stops where most of the total stop time (TST) is scheduled. Recent bubble-based algorithms limit calculated bubble profusion and size and prescribe decompressions with TST skewed toward deeper stops. Navy Experimental Diving Unit (NEDU) has completed a controlled comparative study of these approaches.



MATERIALS AND METHODS: Divers wearing swimsuits and t-shirts, breathing surface-supplied air via full face masks, and immersed in 86 OF water in the NEDU Ocean Simulation Facility wetpot were compressed at 60 fsw/min to 170 fsw. They performed 115 Watt cycle ergometer work during an ensuing 27.2 minutes at bottom and were decompressed at 30 fsw/min with stops prescribed by one of two schedules, each with 174 min TST. Schedule 1, with first stop at 40 fsw, was prescribed by the man-tested, deterministic gas content, WALl8 Thalmann Algorithm. Schedule 2, with first stop at 70 fsw, was the optimum distribution of TST according to the manndive calibrated, probabilistic BVM(3) bubble model. Decompression sickness (DCS) incidence with these schedules was compared under the sequential stopping rules of reject-high if DCS risk > 7% or reject-Iow if DCS risk < 3% with 95% confidence.



RESULTS: The trial was terminated after midpoint interim analysis. Neither schedule was rejected, but DCS incidence in Schedule 2 (deep stops, 11 DCS/198 dives) was significantly higher than in Schedule 1 (3/192, p=0.030, one-sided Fisher Exact). On review, one Schedule 2 DCS was excluded, but the result remained significant (p=0.047). Most DCS was mild, late onset, Type I, but two Schedule 2 cases involved rapidly progressing CNS manifestations.



CONCLUSIONS: The deep stops schedule had a greater risk of DCS than the matched conventional schedule. Slower gas washout or continued gas uptake offset benefits of reduced bubble growth at deep stops.

UHMS ASM . 2007
Session A

A4 (President's Competition) Oral Presentation: 0939 - 0951 Poster Presentation: 1045 - 1200



DIFFERENCE IN BUBBLE FORMATION USING DEEP STOPS IS DEPENDENT ON LENGTH OF BOTTOM TIME; EXPERIMENTAL FINDINGS AND THEORETICAL SUPPORT



Gutvik CR, M0l1erh:Jkken A, Brubakk AO



Baromedical and Environmental Physiology, Department of Circulation and Medical Imaging, Norwegian University of Science and Technology, Norway



BACKGROUND: Deep decompression stops compared to more conventional shallower stops have recently been introduced. Most findings and theoretical work on excess gas phase models suggest an apparent advantage of using deeper stops. However, some reports indicate that the incidence and/or risk of decompression sickness may actually increase following such procedures.



MATERIALS AND METHODS: The impact of different decompression schedules was tested on pigs compressed in a dry chamber monitored using ultrasonic imaging. A total of 26 pigs were divided into 4 groups of 6 and one group of 2 (aborted protocol). Two groups performed a shallow/long (30 msw / 70 min) dive. One group followed a Buhlmann / Uwatec decompression procedure while the other followed a procedure generated by the Copernicus bubble model. The three last groups did a deep/short (65 msw / 20 min) dive followed by a Buhlmann decompression procedure, a Copernicus procedure (aborted profile) and a revised Copernicus procedure respectively.



RESULTS: The long/shallow dive achieved a significant decrease of vascular bubbles following the procedure with deeper initial stops (Copernicus schedule) compared to the controls (Buhlmann schedule). However, on the deep/short dive the procedure with deeper stops gave a dramatic increase of bubble formation, resulting in the protocol to be aborted after two trials. A new revised Copernicus schedule with the deepest stops removed, gave a significant decrease of vascular bubble formation.


CONCLUSIONS: A new stabilizing mechanism for bubble nuclei had to be developed in order to simulate and reproduce the findings in this study. "Traditional" bubble models will in general suggest that adding some deep stops is beneficial for decompression outcome, however this may not always be true. The presented studies suggest that deep stops are not recommended on shorter dives.
 

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Jonah
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7,366 Posts
Thanks for posting that Mark. I assume these are just abstracts, have you read the full papers?

I'd be particularly interested to compare the stop schedules for the Copernicus / revised Copernicus conditions for the 60m dive in the second study.
 

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Nigel Hewitt
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OK so we gather that if you dive WALl8 Thalmann Algorithm, probabilistic BVM(3) bubble model or the Copernicus system you get bent at least once a year or more.

I think I'll stick to what I use now.
I wish we had some stop times to compare as 11 bends in 198 dives for the bubble model does seem a bit nasty so if anybody can find the full papers...

...Or we could just say "US Navy report pans bubble models" and save ourselves having to think. Some of the early bubble stuff made BSAC88s look conservative but had deep stops but I doubt this is that old.
 
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Mark Milburn
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Discussion Starter · #5 ·
From what I know this is so new it hasn't been released yet. It's being kept quiet for now, typical. Probably waiting for the response from all the bubble model experts to make an excuse about pigs being unable to hold their stops properly or doing fast ascents :D

Tom I'll see if there is any more stuff lying around out there.

It does read that the Copernicus model bent every pig so they had to use a modified version. It's also interesting that deep stops work on longer shallow dives, which weren't actually that deep to start with.
 

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Jonah
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I think to interpret the findings properly, one would need to know what is meant by 'deep' in the context of this research - could have quite different implications.

For example, on the 60m dive, would one class a 50m stop as 'deep' or a 30m stop as being deep, etc etc.... more information needed basically.
 

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Long time no sea
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Shit - I'm a pig (ask my wife) , I can't hold stops for toffee and I got bent. shurely shum coincidence.

Neill

bought a Vytec DS lately? - oh hahahahahahaha.
 

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Resident bibliophile
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For the record, these have not been published or released and this is a copyright violation. <g> They were presented week before last at the Undersea and Hyperbaric Medical Society (UHMS) Meeting in Maui.

That said, I do have the posters from these presentations and as soon as I am allowed to post these, I'll update the thread (couple more weeks maybe). Wayne and David are currently working on the final paper of the USN data and it should be out shortly after they finish.
 

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For the record, these have not been published or released and this is a copyright violation. <g> They were presented week before last at the Undersea and Hyperbaric Medical Society (UHMS) Meeting in Maui.

That said, I do have the posters from these presentations and as soon as I am allowed to post these, I'll update the thread (couple more weeks maybe). Wayne and David are currently working on the final paper of the USN data and it should be out shortly after they finish.
I understand the copyright thing Gene, no argument there. However if they papers were presented to a meeting, is this not a release?

Adrian
 

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What he posted is freely available on the UHMS website. But to be fair maybe it should just be linked instead of block copy and paste.
Interesting, that was not supposed to happen until after the Journal Supplement was actually published. (We still had changes being turned in the last day of the meeting that will go into the final publication of the Supplement in a month or so.) UHMS does have pdf's of the oral and posters available for sale but I am not sure how that will be handled. (I made the CD's at the meeting but it is up to them now.) Probably best to contact them directly (cost was $US20.00 at the meeting and will be more to non-members and member/ non attendees).

It they plan to leave the abstracts online now, I will request permission to add them to the database now and not wait for the Supplement. Again, I will let you know when I know more. We did get permission to add the posters for these two abstracts from the authors.

Gene, has the work been through a peer-review process prior to the UHMS meeting?
The abstracts are reviewed by the Scientific Committee. It is a formal peer review though it is not the same as what we use for journal articles.

Thanks for your patience!
 

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Mark Milburn
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Discussion Starter · #13 ·
For the record, these have not been published or released and this is a copyright violation. They were presented week before last at the Undersea and Hyperbaric Medical Society (UHMS) Meeting in Maui.
If they wish the above post to be removed I shall remove it, but I think that this information is very important to divers.

How many more people do you want to get DCI before the information is made public?
 

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aka Chimp 1 or Mavis...
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Mark, you didn't quote the <g> of Gene's which does change the tone somewhat of the quote.

I don't think anyone wants more people to gtbent, but it does take a little time to get these things into the public from having the presentations made. Admittedly, they should have this info ready to go, but you know what bureaucracy is like :D

I am sure it will come out shortly but I am pretty sue that those who dive air to 170fsw (which is how I read the report synopsis depths) won't read the report :D
 

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1/2 of slut divers
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bought a Vytec DS lately? - oh hahahahahahaha.
Yeah........................

But in its defence, it doesnt tend to give deepstops on shorter dives - which is what the report said was bad. And its not bent me yet!

But consider that all peoples physiologies are different, people wont always react in the same way as the test subjects under the same conditions.
 

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Deep stop schedule.

Yeah........................

But in its defence, it doesnt tend to give deepstops on shorter dives - which is what the report said was bad. And its not bent me yet!.
Then you read it differently to me. It says that they ran two schedules, each with 174 min TST - i.e the total stop time was the same on both schedules. Which means the deco curves are different shapes.

Don't know about you, but when I do deep stops it adds to the shallow stop time. I'd anticipate more incidence of DCS if you ran the same total stop times but with more of it done deep.
 

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It doesn't matter how many of these things I read, it ALWAYS comes back to the point.

Deco is theory, we all differ from each other, we all differ to ourselves yesterday and will be different again tomorrow.

BOTTOM LINE
If it works for you - do it!

If it gets you out of the water feeling good - then it's worked. If you get out of the water feeling tired then you're not as clean as you could be.

Juz
 

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1/2 of slut divers
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Then you read it differently to me. It says that they ran two schedules, each with 174 min TST - i.e the total stop time was the same on both schedules. Which means the deco curves are different shapes.

Don't know about you, but when I do deep stops it adds to the shallow stop time. I'd anticipate more incidence of DCS if you ran the same total stop times but with more of it done deep.
I'm sure there was a bit in the report that said deep stops are not encouraged on shorter dives - presumably because they contribute to further loading of the tissues which most likely wont be saturated due to the shorter dive time.

Anyway. My vytec will knock a minute or so off the 6m stop if I complete a couple of deep stops. My buddys vytec, which was bought soon after mine, does the same. Don't know if there is a software update between ours and yours?? Assuming you use a vytec DS of course??!!
 

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Resident bibliophile
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Mark, you didn't quote the <g> of Gene's which does change the tone somewhat of the quote.

I don't think anyone wants more people to gtbent, but it does take a little time to get these things into the public from having the presentations made. Admittedly, they should have this info ready to go, but you know what bureaucracy is like :D

I am sure it will come out shortly but I am pretty sue that those who dive air to 170fsw (which is how I read the report synopsis depths) won't read the report :D
Thanks GLOC.

General consensus was to use the following until the supplement is published:

Gutvik CR, Møllerløkken A, Brubakk AO. DIFFERENCE IN BUBBLE FORMATION USING DEEP STOPS IS DEPENDENT ON LENGTH OF BOTTOM TIME; EXPERIMENTAL FINDINGS AND THEORETICAL SUPPORT. Undersea and Hyperbaric Medicine. Vol. 34 Supplement. In press.

Gerth WA, Gault KA, Doolette DJ. EMPIRICAL EVALUATION OF THE EFFICACY OF DEEP STOPS IN AIR DECOMPRESSION DIVES. Undersea and Hyperbaric Medicine. Vol. 34 Supplement. In press.

Until the proceedings are back from the printer they are unpublished works. Some journals can and will refuse to publish work that has been published before (and this does count) so it is NOT as simple as it should be. You will notice that UHMS does not seem to care or I would have asked for this thread to be taken away. But we should be responsible for our actions and ignorance is NOT an excuse.

And on a personal note: The UHMS has been VERY easy to work with and show exceptional support for us by allowing Rubicon to place their journals online after a one year embargo. Their desires are worth consideration as are the thoughts of other journals that are watching and considering our project for distribution of their works. It has taken ME years to build this into something worth while and it would take seconds for the permissions to go away if anyone complained.

Back on topic... (and please PM with any other copyright issues as to not degrade this thread)

Kieth posted the USN Study profile in this thread on TDS.

kgault said:
170fsw for 30 min -- 174 min of stop time

Profile 1 - Deep Stops (stops distributed by BVM3 model)

70 fsw 12 min
60 fsw 17 min
50 fsw 15 min
40 fsw 18 min
30 fsw 23 min
20 fsw 17 min
10 fsw 72 min

Profile 2 - Shallow Stops (Haldanian style - VVAL-18)

40 fsw 9 min
30 fsw 20 min
20 fsw 52 min
10 fsw 93 min

The elongated schedule was to allow for testing of a significant difference in outcome between the two profiles with a limited number of dives (375 dives on each), and to get the trial through our IRB committee with acceptable risk estimates of each schedule by models that selected the alternate style of decompression.

As to the over decompressing, there was a 1.5% observed incidence of DCS cases for the shallow stop and about 5% for the deep stops. These values are consistent (within error limits) of the values used to select the profiles.

Keith
 

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Finless: You couldn't invent him...
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I don't care .......... I believe Mr Pyle!

Maybe deep stops are bad if you aren't into deco ............ but that's going to be unlikely I suppose?

Oh well, I'll stick to what my Cochran Commander + 10% tells me + a couple of deep stops.

Perhaps I'll turn my wreck dives into virtual reef dives ............. 10 minutes at the bottom and then 50 minutes crawling up to the surface whilst dreaming about reefs and walls and ledges etc?
 
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