Info Deeply Safe Labs: A website for dive computer testing

[Deeply Safe Labs]

Hi @cerich ,

Thank you for this very large collection of articles. As there is a lot to read, I have chosen to split the work between the team members and make my response based on their feedback. If there is anything that we missed in these articles, please let us know.

These articles are quite interesting. They mention ventilation/perfusion, patent foramen ovale and decompression sickness in general. However, none seem to be pertinent in regard to what Pr A. A. Bühlmann talked about in the aforementioned UHMS workshop.

You are asking whether we understood the meaning correctly. Let me quote another part of that workshop:

Micro-bubbles in the venous blood, obstructing a part of the lung capillaries, produce a ventilation-perfusion disturbance. The result is a right-to-left shunt, well known in lung-physiology.

This quote is crystal clear. The bolded parts are self explanatory. Moreover, it is an affirmation. I don't pretend having the skills to deny this affirmation.

If there is something that we have misunderstood, I ask that you please express it clearly, using quotes form articles that you reference, for multiple reasons.

First, not all readers from this forum may want to read full articles just to understand a point.

Second, the Deeply Safe Labs team is working for free. You will notice that our website had no advertising, no cookies, no Google APIs... What we do, we do for the community, not for ourselves. We have jobs alongside that, please, spare us the time spent combing through that many articles. I would also appreciate, as might other readers, that you refrain from using acronyms without defining them beforehand.

Lastly, while I have no doubt on your good faith and willingness to make the debate constructive, an inattentive reader may interpret your unquoted bibliography as an attempt to flood them with information and confuse them.

Now, let's be constructive and leave these petty arguments behind us. You seem to disagree with us, and that's fine, but please make your point clearly:
Which claims exactly are you denying? Why?
Do you have a specific example of a computer that, in its manual, makes a mention of a scope of use that we would have breached?

I will also point out that you haven't answered my last question.

Best regards,
Eric Frasquet,
Deeply Safe Labs.

 

[Johnoly]

.... I would add that anatomic AV intrapulmonary shunts have been documented in healthy adults as well.

Had to google that one. How the heck would you even find this DCS "problem",,,a 128/256 slice CT scan?

 

[duke dive medicine]

Had to google that one. How the heck would you even find this DCS "problem",,,a 128/256 slice CT scan?

View attachment 833706

Great illustration!!

You typically wouldn't find it until it somehow declared itself. Even then it would be a presumptive diagnosis because it's too small to see on imaging. An example might be a diver who experiences a couple of instances of sudden-onset neurological DCS, has a transthoracic echo with bubble contrast to check for PFO, doesn't have any type of cardiac septal defect but has delayed bubbles in the left heart.

Best regards,
DDM

 

[cerich]

Hi @cerich ,

Thank you for this very large collection of articles. As there is a lot to read, I have chosen to split the work between the team members and make my response based on their feedback. If there is anything that we missed in these articles, please let us know.

These articles are quite interesting. They mention ventilation/perfusion, patent foramen ovale and decompression sickness in general. However, none seem to be pertinent in regard to what Pr A. A. Bühlmann talked about in the aforementioned UHMS workshop.

You are asking whether we understood the meaning correctly. Let me quote another part of that workshop:



This quote is crystal clear. The bolded parts are self explanatory. Moreover, it is an affirmation. I don't pretend having the skills to deny this affirmation.

I think he conflated two different issues actually, because right-left shunt (again, using right -left is specific, and applies in heart, not in lungs) in the lungs doesn't make any sense. Even if he was somehow connecting them together in a way I can't conceptualize (and no question, it was his field, so it is possible). Regardless, is it reasonable to design a dive computer or algorithm based on a right-left shunt that would only be present in ~25% of the general population, who physiologically a strong argument can be made they should not be diving anyhow. Shunting, or any type, is something that so many factors would influence, many FAR outside a dive computers ability to know, that no amount of programming in the world would work. It becomes extrapolations of assumptions. This goes back to a computer that may as well just tell you "do not dive" when you turn it on.

If there is something that we have misunderstood, I ask that you please express it clearly, using quotes form articles that you reference, for multiple reasons.

First, not all readers from this forum may want to read full articles just to understand a point.

Second, the Deeply Safe Labs team is working for free. You will notice that our website had no advertising, no cookies, no Google APIs... What we do, we do for the community, not for ourselves. We have jobs alongside that, please, spare us the time spent combing through that many articles. I would also appreciate, as might other readers, that you refrain from using acronyms without defining them beforehand.

OK, will use acronyms but also what they mean to make it easier. I didn't think i had been using any that should be unfamiliar to someone that is making the assertions or claims regarding this subject like your team is.

Lastly, while I have no doubt on your good faith and willingness to make the debate constructive, an inattentive reader may interpret your unquoted bibliography as an attempt to flood them with information and confuse them.

I am presenting information that is part of a foundation, quoting , or cherry picking to support my argument may be helpful sometimes, but it can also easily be done to simply support my position or opinion. So, yeah, it's a flood of information, but this subject is fairly complex and requires a solid foundation of knowledge. There is a couple things going on here, one is addressing your claims, the other that is secondary IMHO (in my honest opinion) is educating those following this thread so they can come to own conclusions

I will also point out that you haven't answered my last question.

Best regards,
Eric Frasquet,
Deeply Safe Labs.

How many of the units you list are intended for recreational no stop divers? I believe that is a clue. Once you eliminate those, a look into manuals will in some cases show more pertinent information

 

[dmaziuk]

What we are saying is that ZH-L16 C implementations that we have tested do not account for repetitive dives in any other way that simple offgasing during the surface interval.

That is indeed how ZH-L model works.

Generally speaking, since the off (in this case) -gassing is a log curve, it never goes down to zero, resulting in a residual build-up in the slower tissues over repetitive dives. Exactly how much, can be controlled by adjusting your tissue compartment half-times to fit your "penalty" target. Other models can do it by e.g. adding "Gradient Reduction" fudge factors, and that's perfectly fine. But so is the Haldanean Way, as long as it gets the diver out of the water not bent.

As for the proposed schedule of 6 dives to 16 minutes to 30 metres, you may want to read the DSAT report(*), specifically chapter V. In a nutshell, on a 6 dives/day schedule somewhat less aggressive than the above, they bent their test diver on day 2.

(Said report also has a picture of that theoretical residual build-up: figure 6 on page 45.)

*) The DSAT Recreational Dive Planner: Development and validation of no-stop decompression procedures for recreational diving by R. W. Hamilton et al., 1994

Why is any of this news?

 

[tursiops]

*) The DSAT Recreational Dive Planner: Development and validation of no-stop decompression procedures for recreational diving by R. W. Hamilton et al., 1994

Available on ScubaBoard at Info - The DSAT Recreational Dive Planner (RDP), 1994.

 

[Nick_Radov]

What we are saying is that ZH-L16 C implementations that we have tested do not account for repetitive dives in any other way that simple offgasing during the surface interval. We first confirmed this with theoretical calculations, and contacted relevant manufacturers to bring this to their attention. Some of them simply confirmed that absence of additionnal procedures, without bringing any argument to why they are not taking into account aggravating factors, like the right-left pulmonary shunt.

This is silly. Anyone with a significant shunt (PFO or otherwise) shouldn't be diving in the first place — or at least shouldn't be doing repetitive dives or anything close to the NDL. Conversely, if a diver has a shunt there is no reliable scientific evidence that any particular deco algorithm can make it safe for them to do aggressive repetitive dives; there are more variations in individual pathology than any algorithm could account for. When dive computer manufacturers add "additional procedures" those are typically just arbitrary adjustments without any solid scientific basis or clear documentation.

I appreciate that you're trying to help, but I think you have lost the plot and are only confusing people. Divers shouldn't make purchase or usage decision based on your test results. If you want to actually make a positive contribution then run a real scientific study with a bunch of subjects doing repetitive dives on a variety of profiles and see who gets bent. Then you will have a factual basis for your claims. Otherwise you're just guessing.

 

[TooCold]

Interesting data on your website @Deeply Safe Labs (Eric). Thanks for all the work!

Some of them simply confirmed that absence of additionnal procedures, without bringing any argument to why they are not taking into account aggravating factors, like the right-left pulmonary shunt.

Whatever the importance of this or any other physiological factors to DCS risk, the fact is that if a dive computer can't measure something then it can't use it in its algorithms. One thing everyone knows (or should) about their dive computer is that it knows NOTHING about the diver as an individual, but merely implements a theoretical model that hopefully provides safe diving guidelines for most divers most of the time.

From Deeply Safe Labs:
"A modern dive computer, supposed to cover this type of practice, should offer a decompression profile closer to what Albert Bülhmann and his colleagues considered an indispensable evolution ..."
By "this type of practice" you mean the Bülhmann 6 dive series you test? But I don't expect to EVER do a series of 6 16 minute dives to 30m all in less than 9 hours. I don't expect to ever find out if my dive computers' implementations of ZH16LC are appropriate for that kind of profile, and I don't care. It's got to be a vanishingly small proportion of divers accurately modelled by that protocol. So if that dive protocol is what led to the conservatism of ZH8L ADC then why should I be concerned, since I don't, and won't dive that way?

and
"At the very least, the manufacturer should clearly indicate the limits of use of the algorithm used in the dive computer in question."
What sort of limits do you have in mind, and how specific should they be? DC manufacturers are not in the business of conducting scientific research into diving pathophysiology - nor should they be. Isn't it enough for a manufacturer to
to clearly - and accurately - specify what algorithm is implemented?

So, it seems to me that you are overgeneralising from your data. It may well be the case that FOR THE STUDIED 6 dive protocol the ZH16L C algorithm is not conservative enough. But it is unwarranted on that evidence alone to conclude that ZH16L C cannot be trusted for the type of repetative diving done by the vast majority of divers.

 

[Deeply Safe Labs]

Hi everyone,

None of this is about a patent foramen ovale (PFO). With a PFO, some microbubbles are bypassing the lungs through the foramen ovale. Here, Pr A. A. Bühlmann is identifying a phenomenon that involves microbubbles actually going through the lungs, which isn't what PFO is about. He also seems to believe that this phenomenon can and should be implemented in dive computers, and never has he implied that it only affects part of the population. I will not continue arguing around about a point that is so obviously not what we are talking about.

Thank you @dmaziuk for mentioning that article, and thank you @tursiops for the link. This test protocol is very interesting, it would be easy enough to reproduce based on the data in appendix C2. We could reproduce the same profiles and compare the remaining no decompression times at the end of each level. However, it is quite lengthy, and would require quite some time to complete. What is your prediction on the results we'll get?

So, it seems to me that you are overgeneralising from your data. It may well be the case that FOR THE STUDIED 6 dive protocol the ZH16L C algorithm is not conservative enough. But it is unwarranted on that evidence alone to conclude that ZH16L C cannot be trusted for the type of repetative diving done by the vast majority of divers.

This protocol is indeed rather aggressive, but as for the R.W. Hamilton et al. DSAT study, this protocol is not of our making, but comes from the aforementioned UHMS 1994 workshop, and was engineered by Pr A. A. Bühlmann himself. This protocol, while including 6 dives, can be used to represent 2, 3, 4 or 5 dives. I agree that we cannot generalize from our results regarding even more aggressive profiles. However, regarding "lighter" dives, as done by the vast majority of divers, it gives a really strong idea, don't you think?

@cerich you still haven't answered my question. We are all for correcting our potential mistakes and flaws in our analysis, but you are not making it easy. Please, kindly stop beating around the bush and get to your actual point. What computers exactly do you believe not to be intended of recreational use? What exact part of the manuals of said computers have we missed?

Best regards,
Eric Frasquet,
Deeply Safe Labs.

 

[cerich]

Hi everyone,

None of this is about a patent foramen ovale (PFO). With a PFO, some microbubbles are bypassing the lungs through the foramen ovale. Here, Pr A. A. Bühlmann is identifying a phenomenon that involves microbubbles actually going through the lungs, which isn't what PFO is about. He also seems to believe that this phenomenon can and should be implemented in dive computers, and never has he implied that it only affects part of the population. I will not continue arguing around about a point that is so obviously not what we are talking about.

I believe you feel it is obvious, to many of us that know this subject well and reading your statements and conclusions, we don't agree. It's like you feel you found some magic key in a very old paper quote and are running with it, but excluding everything else. Given that the quote includes right-left shunt, you can keep on insisting it isn't PFO and heart, but until you can identify what on earth would cause a specifically right-left shunt in the lungs to match the quote you are running with, how on earth can you be so certain and feel is obvious?

Thank you @dmaziuk for mentioning that article, and thank you @tursiops for the link. This test protocol is very interesting, it would be easy enough to reproduce based on the data in appendix C2. We could reproduce the same profiles and compare the remaining no decompression times at the end of each level. However, it is quite lengthy, and would require quite some time to complete. What is your prediction on the results we'll get?



This protocol is indeed rather aggressive, but as for the R.W. Hamilton et al. DSAT study, this protocol is not of our making, but comes from the aforementioned UHMS 1994 workshop, and was engineered by Pr A. A. Bühlmann himself. This protocol, while including 6 dives, can be used to represent 2, 3, 4 or 5 dives. I agree that we cannot generalize from our results regarding even more aggressive profiles. However, regarding "lighter" dives, as done by the vast majority of divers, it gives a really strong idea, don't you think?

@cerich you still haven't answered my question. We are all for correcting our potential mistakes and flaws in our analysis, but you are not making it easy. Please, kindly stop beating around the bush and get to your actual point. What computers exactly do you believe not to be intended of recreational use? What exact part of the manuals of said computers have we missed?

I did answer you, start with intended use for a quick gross elimination of many you tested, then look at the manuals of what is left. The thing is, you SHOULD know EXACTLY what all of the intended use and manuals are of all of them you tested when you embark on a crusade claiming they are unsafe because of a quote you read that, once again, is not physiologically accurate to the lungs. If you want me to join your team and do some of the work you should be doing, ask me, i will consider it. Forewarning, I am not a wallflower and love debating and learning.

Best regards,
Eric Frasquet,
Deeply Safe Labs.