Deep Stops Increases DCS

[Dr Simon Mitchell]

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.

Is the following an OK basis for my "guessing" that you use a bubble model AJ (post 398 on this thread)?

I dive VPM-B and feel fantastic after all my dives. I have also used GF and also feel fine. I trust VPM and it works great for me and many others.

You strongly admonished someone else for appearing to not appreciate the importance of bubble formation, after diving and suggested that a Doppler bubble evaluation might force them to rethink their approach to decompression.

I have referred you to a study in Journal of Applied Physiology in which use of your chosen bubble model almost invariably resulted in high post dive bubble grades after mixed gas technical dives.

Are you going to take your own advice?

Simon M

 

[lowviz]

Apologies for the second interruption, but would you mind giving your opinion as to the value of purchasing an inexpensive doppler bubble monitor. (something like: Buy Edan - Sonotrax Basic, 8mhz Sensor Vascular Doppler -online)

My personal experience is that an 8MHz probe seems best as it allows one to clearly distinguish between artery and vein in the neck. Anything better?

Bought one quite a while ago. So what is today's best option as far as a quick, relatively inexpensive, and easy check for bubbling?

 

[ajduplessis]

Doppler is only a tool. You need to evaluate a Doppler recording in order to determine bubble scores.

5-8Mhz is fine.

 

[rossh]

Is the following an OK basis for my "guessing" that you use a bubble model AJ (post 398 on this thread)?



You strongly admonished someone else for appearing to not appreciate the importance of bubble formation, after diving and suggested that a Doppler bubble evaluation might force them to rethink their approach to decompression.

I have referred you to a study in Journal of Applied Physiology in which use of your chosen bubble model almost invariably resulted in high post dive bubble grades after mixed gas technical dives.

Are you going to take your own advice?

Simon M

The test procedure that is referenced above (here), was studying for the presence of arterialized Venous Gas Emboli (artVGE) in normal dive conditions. They found that 42% of dives to make artVGE. There were no DCS cases. The Result says "This study demonstrates that after open-sea trimix diving, a right-to-left crossover of the venous gas emboli occurred in 5 of 7 divers and in 9 of 21 dives."

The significance of this I imagine, would be that it emulates the PFO condition, and demonstrates that artVGE are common place, even in non PFO divers..

Naturally in order to run the test, they needed to makes lots of VGE - hence the choice of a maximum efficiency profile. I have no doubt that a ZHL-C profile, configured at maximum efficiency, would have done the same job.


This same research team went on to measure how common artVGE will be after a dive when adding normal post dive stress.

Exercise after SCUBA diving increases the incidence of arterial gas embolism.

They found 13% of divers made artVGE by just resting, and a further 39% of divers will created artVGE from the strenuous activities, much like the ones we engage in such as, climbing the ladder, or walking the gear back to the car on a shore dive. So typically, half of us will experience artVGE after any dive.

Which might make you wonder - given how common artVGE really are (50%), are they harmful?

********

The reality is, all divers can make VGE, most diver do make VGE, and all models make VGE. All gas types make VGE, and trimix makes more VGE. NDL divers will make VGE, recreational divers make VGE. Even breath-hold divers can make grade 4 VGE from a single breath of air (UHM 2016, Vol. 43, No. 4 – VENOUS GAS EMBOLI AFTER BREATH-HOLD DIVES)

VGE were first discovered in the early 70's by Spencer, and he named his grading system based on data from very shallow stop style profiles. papers with Spencer; We divers have all been making VGE ever since then, and will continue to do so.

.

 

[ajduplessis]

Is the following an OK basis for my "guessing" that you use a bubble model AJ (post 398 on this thread)?

You strongly admonished someone else for appearing to not appreciate the importance of bubble formation, after diving and suggested that a Doppler bubble evaluation might force them to rethink their approach to decompression.

I have referred you to a study in Journal of Applied Physiology in which use of your chosen bubble model almost invariably resulted in high post dive bubble grades after mixed gas technical dives.

Are you going to take your own advice?

Simon M

Yes I indicated that bubbles do exsist as is evedent is the reference you provided. The member described imaginary bubbles and I suggested a Doppler to prove bubbles exist.

You then concluded your own observations including referencing trimix bubble score into a AIR diving study to somehow support your believes. Do these 2 type of a gasses behave the same? You will also know that even if bubbles are present they migh not result in an injury. So please again clarify what you are on about.

Your multi level study because it sure as h3ll is not a deep stop, concluded which is common sense to even beginners. The the deeper and longer you stay submerge the greater the risk.

Lastly you provided through your studies great examples how not to plan and execute a dive.

 

[ajduplessis]

Where do you guys keep your goats?

Apparently the navy

 

[Dr Simon Mitchell]

I suggested a Doppler to prove bubbles exist.

You suggested, in very strong terms, that a diver might want to rethink their decompression strategy if their present approach produces a lot of bubbles.

I have pointed to evidence that your approach produces a lot of bubbles.

I can't put it any more simply.

You then concluded your own observations including referencing trimix bubble score into a AIR diving study to somehow support your believes. Do these 2 type of a gasses behave the same? You will also know that even if bubbles are present they migh not result in an injury. So please again clarify what you are on about.

I never mentioned the NEDU study in this exchange with you or drew any parallels with it. I am merely pointing out the apparent irony in your unrelenting defense of a decompression strategy proven to produce high bubble counts after strongly advising someone else that they should rethink their approach under similar circumstances.

Simon M

 

[Dr Simon Mitchell]

The test procedure that is referenced above (here), was studying for the presence of arterialized Venous Gas Emboli (artVGE) in normal dive conditions.

Correct

They found that 42% of dives to make artVGE. There were no DCS cases. The Result says "This study demonstrates that after open-sea trimix diving, a right-to-left crossover of the venous gas emboli occurred in 5 of 7 divers and in 9 of 21 dives."

They also found that the vast majority of divers produced high venous bubble grades after the dives.

The significance of this I imagine, would be that it emulates the PFO condition, and demonstrates that artVGE are common place, even in non PFO divers.

Correct, but more accurately, arterialised VGE are common place when venous bubble grades are very high.

Naturally in order to run the test, they needed to makes lots of VGE - hence the choice of a maximum efficiency profile.

This is confabulation. Nowhere in the paper does it suggest that the profiles were chosen to be particularly bubble-generating. Indeed, it reads as though these were routine training dives conducted as they are always conducted:

"The participating divers were active members of Croatian and Slovenian Search and Rescue units, and the measurements were taken during their scheduled exercise in technical diving with trimix".

Indeed the authors appeared surprised by the consistently high VGE production:

"Diving profiles and decompression protocols performed by this group of divers were based on a trimix bubble model that keeps the predicted bubble volume below some calculated critical level. Although the diving excursions in this study were supposedly conservative according to the decompression algorithm used, a high incidence of high-grade VGE was detected. This may be due to the fact that the critical level is set too high and thus the decompression may not be sufficient".

It certainly does not suggest they chose the profiles for high bubbling. Indeed they considered them to be "conservative". It is a flaw of the paper that they do not explicitly say which conservatism level VPM was used at, but out of interest, where do you find reference to "maximum efficiency"? And what, exactly, do you mean by that? Do you mean low conservatism level?

I have no doubt that a ZHL-C profile, configured at maximum efficiency, would have done the same job.

This may or may not be true (which is why you need comparative studies) but I fail to see the significance. The point is that the bubble model used in this experiment did a very poor job at preventing bubble formation. This is consistent with the findings of the NEDU and French studies, and the clear implication of these is that there is probably a better approach. It may not be an unmodified ZHL-C profile, but that is irrelevant.

This same research team went on to measure how common artVGE will be after a dive when adding normal post dive stress...snip...So typically, half of us will experience artVGE after any dive.

Which might make you wonder - given how common artVGE really are (50%), are they harmful?

If you really want to understand this issue, and why a significant proportion of divers may form VGE and even arterialise those bubbles without apparent harm then read this:

Mitchell SJ, Doolette DJ. The pathophysiology of microbubbles crossing a PFO or other right to left shunts in decompression sickness. In: Denoble PJ, Holm JR eds. Patent Foramen Ovale and Fitness to Dive Consensus Workshop Proceedings. Durham NC, Divers Alert Network, 43-50, 2015.

Which can be downloaded from :
https://www.diversalertnetwork.org/...Proceedings/2015-pfo-workshop-proceedings.pdf

The reality is, all divers can make VGE, most diver do make VGE, and all models make VGE. All gas types make VGE, and trimix makes more VGE. NDL divers will make VGE, recreational divers make VGE. Even breath-hold divers can make grade 4 VGE from a single breath of air (UHM 2016, Vol. 43, No. 4 – VENOUS GAS EMBOLI AFTER BREATH-HOLD DIVES)

VGE were first discovered in the early 70's by Spencer, and he named his grading system based on data from very shallow stop style profiles. papers with Spencer; We divers have all been making VGE ever since then, and will continue to do so.

And what is your point? Are you saying bubble modellers don't worry about bubbles anymore? Are you suggesting that reducing VGE is not a legitimate goal in decompression planning (in which case I would ask you why the DCIEM table development program was based on exactly that)? Are you trying to suggest that VGE are harmless (in which case I would ask you to explain the unequivocal links between PFO and serious neurological DCS)? We have been down this road before Ross, and I doubt that you want to go down it again.

Simon M

 

[Dr Simon Mitchell]

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

I very much doubt it.

Simon M

 

[leadduck]

Yes I indicated that bubbles do exsist as is evedent is the reference you provided. The member described imaginary bubbles and I suggested a Doppler to prove bubbles exist.

Once again: I wrote that the bubble models' bubbles are imaginary. The real world bubbles in your blood, brain, ... are real. You need to distinguish between reality and model, particularly if the bubble model has never been calibrated by controlled experiments, because then you cannot assume any correlation between bubbles in the model and bubbles in reality. I'm not at all surprised about the findings in the paper by Ljubkovic et al., measuring a lot of real bubbles after a dive planned with VPM.