Deep Stops Increases DCS

[lv2dive]

I have to admit I wasn't quite following either. EAN50 is still 50% Nitogen... So it's not the oxygen causing the concern. But I'm a bit slow to keep up with everything on this thread-I don't mean any offense with this only that I'm not sure I understand the meaning.

 

[igor p]

I have to admit I wasn't quite following either. EAN50 is still 50% Nitogen... So it's not the oxygen causing the concern. But I'm a bit slow to keep up with everything on this thread-I don't mean any offense with this only that I'm not sure I understand the meaning.

If you read carefuly quoted posts and the former ones you will see they are talking about oxygen as a problem bor bubbling.

 

[leadduck]

Where did you found this? Can not believe what I read. Never heard one could get hit (DCS) for O2..
Can you please direct me to a study that would support this? Or dokument that would talk about something like this?

I stumbled over it in E.D. Thalmann's paper where he introduces the linear-exponential kinetics that are kind of USN standard today (VVAL18, ...):
http://www.diverbelow.it/attachment...diction using linear-exponential kinetics.pdf

where he writes on p.286 "All models severely underpredicted the DCS incidence for Air and O2 Decompression and Surface Decompression dives. When O2 fractions near 100% are used, all models rapidly drop the tissue PN2 levels and risk rapidly dissipates. The O2 itself is assumed not to contribute to risk in these models."

Another paper from NMRI is: E.C. Parker et al: "Probabilistic models of the role of oxygen in human decompression sickness"
ARTICLES | Journal of Applied Physiology

There the say, previous models severely underpredicted DCS risk when 100% O2 was used for decompression or surface decompression. They had to include two effects to improve the models: (a) high pPO2 causes vasoconstriction and reduces off-gassing, (b) oxygen that's not bound to hemoglobin can bubble just like any inert gas.
This paper also has references to earlier research on oxygen bends.

 

[igor p]

I stumbled over it in E.D. Thalmann's paper where he introduces the linear-exponential kinetics that are kind of USN standard today (VVAL18, ...):
http://www.diverbelow.it/attachments/article/131/Thalmann et alii. Improved probabilistic decompression model risk prediction using linear-exponential kinetics.pdf

where he writes on p.286 "All models severely underpredicted the DCS incidence for Air and O2 Decompression and Surface Decompression dives. When O2 fractions near 100% are used, all models rapidly drop the tissue PN2 levels and risk rapidly dissipates. The O2 itself is assumed not to contribute to risk in these models."

Another paper from NMRI is: E.C. Parker et al: "Probabilistic models of the role of oxygen in human decompression sickness"
ARTICLES | Journal of Applied Physiology

There the say, previous models severely underpredicted DCS risk when 100% O2 was used for decompression or surface decompression. They had to include two effects to improve the models: (a) high pPO2 causes vasoconstriction and reduces off-gassing, (b) oxygen that's not bound to hemoglobin can bubble just like any inert gas.
This paper also has references to earlier research on oxygen bends.

Thanks for this, need to read this...

 

[leadduck]

Regarding DCS with real bubble model deep stops, here is a research report about one DCS case of a dive planned with commercial software (for whoever thinks the NEDU deep stops aren't deep enough or whatever):
https://journals.viamedica.pl/international_maritime_health/article/viewFile/IMH.2015.0010/28403

They take a different approach to comparing ZHL and VPM here, showing how close in % the bubble model deep stop profile comes to the maximally tolerable ambient pressures of ZHL-16A (no GF), and even exceeds it when surfacing for the slow compartments.

 

[emmbee]

I stumbled over it in E.D. Thalmann's paper where he introduces the linear-exponential kinetics that are kind of USN standard today (VVAL18, ...):
http://www.diverbelow.it/attachments/article/131/Thalmann et alii. Improved probabilistic decompression model risk prediction using linear-exponential kinetics.pdf

Well, what do you know...

On Tuesday I said the comparison between deep stops an M-values in Wienke's 2010 paper was invalid because what I called "instantaneous decompression stress function" (and Thalmann "supersaturation risk function") "should have been floored at 0".

Now it turns out Thalmann said the very same thing almost 20 years ago:

Page 258, eq 9: [...] r1n >= 0

That's nice

Thanks for posting this

Matthieu

 

[ajduplessis]

.......Bubble models insert deep stops to limit the growth of their imaginary bubbles and may create stops at a depth

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.

 

[100days-a-year]

Observation of increased venous gas emboli after wet dives compared to dry dives. - PubMed - NCBI

All kinds of cool stuff like this can be found here,I use it to fact check all the Deco(or any) advice I get on Facebook.
Thanks to all for the information presented so far,I won't necessarily change how I decompress on short <20min medium depth dives <200' but will certainly look into any deeper dives I may do.

 

[cerich]

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.

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.

 

[David Doolette]

Where did you found this? Can not believe what I read. Never heard one could get hit (DCS) for O2..
Can you please direct me to a study that would support this? Or dokument that would talk about something like this?

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