Bubble model vs. Gradient Factors redux

[rsingler]

Don't shoot the messenger.

On vBulletin, a ScubaBoard alternative in the UK where Ross still has posting privileges, the usual ranting was underway (just like SB in the old days).
This link prompted the fight:
A new look at Deep Stops
but that's not the interesting part.
This link to a recent interview with Mark Powell came up if you read all the way to page 9:
and it was fascinating! Well worth the 1h20m.
And this little nugget was buried at 19 to 25 minutes into the interview:
DAN is doing something closer to the "Bubble Model vs Gradient Factor" study that we've all been waiting for since Spisni!

It's not quite (it's GF vs. GF), but the implications for deep stops are very suggestive.
And it's not definitive. Nobody died. I don't think anybody got bent. But this came up in the interview, with Powell being cagey about what he could release before DAN publishes the study:
We all bubble. But they didn't deliberately try to bend anyone (unlike NEDU) and apparently few if any divers hit bubble grade 4 with either profile. And the differences between total bubbling with deepish stops and the higher GFLo profile was not statistically significant.
BUUUTT...

Food for thought...
Oh, and Powell now personally dives GF50/XX.

 

[elmo]

Looks like an interesting study. I'm keen to read the report when it's published.

 

[Jack Hammer]

Looking forward to the publishished results.

 

[Marie13]

That was an interesting watch. Thanks.

 

[Storker]

Powell now personally dives GF50/XX.

I believe this is very telling. When deco gurus like Mark Powell and @Dr Simon Mitchell choose to dive GF 50-ish/x, that's because that's what they personally believe is the most prudent choice given what we know now. Regardless of what they choose to recommend in their professional role.

 

[rsingler]

This is just pure speculation, but it's how I tend to look at the graph in the interview:
Since we ALL appear to bubble in our blood (on ultrasound), and yet we know bubbles in other places cause the bends, blood bubbling is just a marker, not a cause. Of course there are catastrophic exceptions, such as a venous to arterial intra-pulmonary shunt or a PFO that then sends a few crucial bubbles to your brain (stroke), your spinal cord (paralysis) or your heart (heart attack).
But for skin or joint bends, what causes bubbles NOT to form, when the blood is bubbling away? As I see it, there are a couple of factors: shear forces and inert gas gradients. Why are we told not to exercise after surfacing? Because tissue shear forces with movement may facilitate bubble formation, just like a cavitating prop. Well, blood zooming at a hundred miles an hour through twisty-turney vessels is a setup for just that sort of phenomenon, where a similarly full fast tissue might just be sitting there like Jello.
Second, the gas gradient in tissue is handled by diffusion. Now, the distance over which diffusion has to take place in a fast tissue may be vanishingly small, as a nearby capillary is standing ready to supply or retrieve gas molecules. But in a joint, for example, accumulated gas molecules have a significantly larger distance to travel in avascular areas before reaching their blood supply. Remember Boyle's bubble in the eye of a decompressing snake in 1670?
The above is what makes this graphic so interesting!

The sheer mass of bubbles says, "Risk!"
But since the bubble grade is relatively low, we know from experience that the DCS risk is, in most cases, similarly reduced.
But the time factor during which higher bubbling occurs cannot be ignored. If, with GF20/85, I'm still bubbling significantly at 90 minutes (or longer), that suggests a direct correlation with other tissues being at risk. We think we know that really fast tissues are able to tolerate higher supersaturation, and perhaps it is in part due to their rich blood supply, whisking away "excess" inert gas before bubbles can grow to dangerous size.
But at the same time, if that prolonged period of risk with GF20/85 is also applied to a slower tissue which, due to deep stops, repetitive dives, great depth or all of the above has accumulated worrisome excess inert gas, then we have a significantly greater period during which gas has to travel an increased distance to reach a capillary, or we have a significantly greater period during which shear forces may play a role, thus potentially allowing a dangerous bubble to form or grow.
I have painted a VERY simplistic picture of complex phenomena, and @Dr Simon Mitchell may tell you that I've misled you significantly (albeit unintentionally). But if venous bubbles have a very coarse correlation with risk, who would you rather be?
This guy?

Or this guy?

 

[Open Ocean Diver]

This is just pure speculation, but it's how I tend to look at the graph in the interview:
Since we ALL appear to bubble in our blood (on ultrasound), and yet we know bubbles in other places cause the bends, blood bubbling is just a marker, not a cause. Of course there are catastrophic exceptions, such as a venous to arterial intra-pulmonary shunt or a PFO that then sends a few crucial bubbles to your brain (stroke), your spinal cord (paralysis) or your heart (heart attack).
But for skin or joint bends, what causes bubbles NOT to form, when the blood is bubbling away? As I see it, there are a couple of factors: shear forces and inert gas gradients. Why are we told not to exercise after surfacing? Because tissue shear forces with movement may facilitate bubble formation, just like a cavitating prop. Well, blood zooming at a hundred miles an hour through twisty-turney vessels is a setup for just that sort of phenomenon, where a similarly full fast tissue might just be sitting there like Jello.
Second, the gas gradient in tissue is handled by diffusion. Now, the distance over which diffusion has to take place in a fast tissue may be vanishingly small, as a nearby capillary is standing ready to supply or retrieve gas molecules. But in a joint, for example, accumulated gas molecules have a significantly larger distance to travel in avascular areas before reaching their blood supply. Remember Boyle's bubble in the eye of a decompressing snake in 1670?
The above is what makes this graphic so interesting!
View attachment 582839
The sheer mass of bubbles says, "Risk!"
But since the bubble grade is relatively low, we know from experience that the DCS risk is, in most cases, similarly reduced.
But the time factor during which higher bubbling occurs cannot be ignored. If, with GF20/85, I'm still bubbling significantly at 90 minutes (or longer), that suggests a direct correlation with other tissues being at risk. We think we know that really fast tissues are able to tolerate higher supersaturation, and perhaps it is in part due to their rich blood supply, whisking away "excess" inert gas before bubbles can grow to dangerous size.
But at the same time, if that prolonged period of risk with GF20/85 is also applied to a slower tissue which, due to deep stops, repetitive dives, great depth or all of the above has accumulated worrisome excess inert gas, then we have a significantly greater period during which the increased distance gas has to travel to reach a capillary, or a significantly greater period during which shear forces play a role, thus allowing a dangerous bubble to form or grow.
I have painted a VERY simplistic picture of complex phenomena, and @Dr Simon Mitchell may tell you that I've misled you significantly (albeit unintentionally). But if venous bubbles have a very coarse correlation with risk, who would you rather be?
This guy?
View attachment 582840
Or this guy?
View attachment 582841

Gosh my thoughts exactly funny how we think the same. Lol

 

[cathal]

Any idea what depth and bottom times were used to achieve this level of bubbling?

 

[ToneNQ]

Extremely interesting. It sent me down the rabbit hole of a number of vBulletin threads, some of which were fascinating in a 'Kardashian' way rather than in a good way.

Hopefully DAN publish soon, I'd love to get a look at the dive profiles and other details.

 

[ChuckP]

Maybe I'm just ignorant and I know money is a factor but....

Why don't they run test dives to 50, 75 and 100m using some Buhlman say 50/80 verses some VGM (or some deep stop model) profile that has what they say is a safety margin similar to GF hi of 80? Or run profiles that are actually dived - Buhlman verses VGM (or some deep stop model) to these three depths, not some recreational depth.

Run the dives and compare bubble formation with doppler ratings.

Don't try to make the run times match, don't add on shallow hang time, just use actual dive plans that people would use. The argument is about which model or planning is better - Bill and Bob want to go dive to 100m for 25 minutes breathing these gases - what's the safest plan to get them out of the water?

Cozumel has three chambers, a great hyperbaric doctor and an island full of dive professionals.........but no money