Deep Stops Increases DCS

[UWSojourner]

NEDU is doing some relevant work on the topic at the moment ...

Where do you guys keep your goats?

 

[igor p]

Hi Igor

The classic paper is Donald KW. Oxygen bends. J. Applied Physiology 1955;7:639-44.

In that paper 7 goats were dived in a chamber to 50 fsw on air for 60 minutes and decompressed to surface over two minutes and none developed DCS. The same goats were dived on another occasion, but this time the chamber was compressed to 50 fsw with air, and then continued to 150 fsw with oxygen (added another 100 fsw~=3 atm of oxygen). So the PN2 was the same for the two dives but the PO2 was very different. After 60 minute bottom time the goats were decompressed directly to surface. After the latter dive, all 7 goats developed transient sign of DCS.
Depth (fsw) 50 150
PN2(atm) 1.99 1.99
PO2(atm) 0.53 3.56
DCS/dives 0/7 7/7

The signs were transient, presumably because the bubbles shrank relatively quickly as the oxygen in them was metabolized by the surrounding tissue.

Occurrence in humans at the more modest PO2 typical of normal diving is not well documented. However, there are anecdotal reports of divers surfacing directly from long decompression stops at 30 fsw breathing oxygen, and developing transient limb pain - just like the goats.

NEDU is doing some relevant work on the topic at the moment that will take about another year to complete.

David Doolette

Thanks David,

how long did the signs persist?
Probably very short time..

Ihor P

 

[David Doolette]

Thanks David,

how long did the signs persist?
Probably very short time..

About 20 minutes. Onset about 5 minutes after surfacing, they would become severe (pain in all limbs, unable to stand, chokes) over the next 10 minutes, and be mostly gone after another 10 or so minutes.

 

[Dr Simon Mitchell]

Imaginary bubbles...... ?WTF? It just amazes me how the ill-informed is the strongest supporter of concepts they clearly dont understand. If you believe bubble formation is imaginary, as is present in your statement above you are going to wake up to a massive shock.....

You should maybe consider a Doppler test after a dive and listen for the evidence and rethink you approach decompression.

Since you obviously (and correctly in my view) consider bubble formation to be important, and since you advocate "rethinking your approach to decompression" based on post dive bubble counts, you might want to have a look at this (Table 1 in particular):

ARTICLES | Journal of Applied Physiology

Simon M

 

[ajduplessis]

Simon I had a look, anything specific you wanted to highlight?

 

[Dr Simon Mitchell]

Simon I had a look, anything specific you wanted to highlight?

AJ,

You just put out a pretty strong statement to the effect that high bubble counts detected after surfacing might make someone want to revise the way they decompress.

I am simply pointing out that in this series of technical mixed gas dives, allegedly controlled by a popular bubble model (which based on your various comments I believe is your approach), high bubble grades were the norm after all the dives.

Simon M

 

[UWSojourner]

In this post I showed some charts that make me think RGBM (had it been tested by the NEDU trials directly) would have performed much like A2 (the deep stop profile with higher DCS incidence). See the "LANL" profile on the charts and the similarities with A2.

The post below from May 2004 seems to indicate Wienke also thought RGBM was similar to the deep profile that was tested, or at least thought so prior to the results of the trials. In 2004 he described the two tested profiles as "Haldane-like" and "RGBM-like". I think I agree with him ... at least with the pre-trials-Wienke.

Hmmmmm ... I wonder. If the NEDU's deep stop "RGBM-like" profile had actually turned out to be the safer profile, would there still have been strong denials of any relationship between A2, RGBM, and VPM?

 

[leadduck]

I think he meant as in the theoretical bubbles the computer algorithm is tracking versus the real bubbles in the divers body. Because I promise you, whatever the computer is tracking...they aren't real bubbles, it is simply math representing the best guess based on the model used to develop the algorithm.

Yes, I wrote "Bubble models insert deep stops to limit the growth of their imaginary bubbles (...)". That doesn't mean there were no bubbles, but just that the bubbles in a bubble model have little to do with the bubbles in tissue.

Of course all models can be just a very coarse approximation of what happens in the body, and you cannot make a strict association between Haldane compartments and body tissues either. However, there is an important difference: In ZHL, parameters such as compartment halftimes and maximum tissue supersaturation were determined experimentally, so that there is a link between particular compartments' supersaturation and real world DCS risk.
Whereas nobody created such model-reality parameter link for the individual compartments of the VPM bubble model. Yount just chose the bubble model parameters so that the total profile runtimes are similar to 1980 USN tables. A correlation between VPM bubble distribution and real bubbles would be coincidental and is unlikely.
Which is a bit paradoxical, because people think VPM would be somehow more accurate regarding bubble count than ZHL because VPM tracks bubbles explicitly in the model equations.

 

[ajduplessis]

Please

AJ,

You just put out a pretty strong statement to the effect that high bubble counts detected after surfacing might make someone want to revise the way they decompress.

I am simply pointing out that in this series of technical mixed gas dives, allegedly controlled by a popular bubble model (which based on your various comments I believe is your approach), high bubble grades were the norm after all the dives.

Simon M

You arrived at your own conclusions rather quickly as usaul. I must also point out that you base this on what you believe (guessing) what my aporoach is witout any context.

Please cite and clarify how you arrived at you conclusions , or rather guess work so I can also know.

 

[David Doolette]

In this post I showed some charts that make me think RGBM (had it been tested by the NEDU trials directly) would have performed much like A2 (the deep stop profile with higher DCS incidence). See the "LANL" profile on the charts and the similarities with A2.

The post below from May 2004 seems to indicate Wienke also thought RGBM was similar to the deep profile that was tested, or at least thought so prior to the results of the trials. In 2004 he described the two tested profiles as "Haldane-like" and "RGBM-like". I think I agree with him ... at least with the pre-trials-Wienke.

Hmmmmm ... I wonder. If the NEDU's deep stop "RGBM-like" profile had actually turned out to be the safer profile, would there still have been strong denials of any relationship between A2, RGBM, and VPM? Hmmmmm.

View attachment 379263

Interesting. That is the workshop, credited in the beginning of NEDU TR 11-06, where the NEDU deep stops trial design was peer-reviewed before the trial commenced. I was unable to attend (it was just prior to my joining NEDU and I was in Australia) but I read all the correspondence, and I have all the presentations from the workshop. They explain that the NEDU Deep stops trial was likely a never-to-repeated opportunity, so the workshop was a "speak now or forever hold your peace" moment to have input on the design, including the schedules, which would be finalized at the workshop. The presentations describe in excruciating detail exactly how the final pair of schedules (A1 and A2) was selected, and exactly what those final test schedules (the ones that were used in TR 11-06) were.

David Doolette