Deep Stops Increases DCS

[nimoh]

The bottom line in this thread is that the indication is being made that deep stops will increase your risk for DCS. This is simply not true as it applies to technical diving.

I haven't read the study, so cannot comment on its validity (and I'm not really qualified to do so anyway). However, I am having trouble following how you can go from your claim that the study is flawed to a claim that its conclusions are untrue. Do you know of other studies that show deep stops either decrease the risk of DCS, or even have no effect on DCS risk?

 

[boulderjohn]

The average tech diver dives whatever algorithm that they have heard is better(better being undefined).
The majority of people in general are cattle AJ. So if you scream loud enough that deep stops are the devil(which by the way is not shown in this study), people will jump on the bandwagon.

Just as everyone jumped on the deep stop bandwagon when it was first being touted.

I would guess is that most people are like me--sifting through the evidence while searching for the right answer. It is important to us because we would prefer not to get bent. We read what we can, and we try to figure out what side makes the most sense. We read the papers with varying degrees of expertise and draw conclusions.

A few years ago a paper was being touted as the reason for the extended stops at the 70 feet--taking advantage of the so called oxygen window. I read that paper, and with my limited scientific background, I decided that the single paragraph that was the source of that rationale made no sense in terms of the science I did know and was unsupported by anything else in the paper. I saw others saying the same thing. Now that paper has gone the way of the dodo, and most--not all--divers have moved away from that practice.

So I am reading this thread, the Rebreather World thread, and a thread I started myself to try to draw a conclusion. I am absorbing as much as I can before I jump to an unwarranted conclusion. Intelligent discussions on the topic are very helpful for people like me. Name calling and personal barbs are not helpful.

Although I am not a scientist, I am quite aware of the scientific process. A science professor at Northwestern and I co-authored a guide for teaching scientific inquiry in science classes, a guide that is still the official stance of the world's largest online education organization. When I examine research for credibility, I look for what I learned through the process of writing that guide. Another part of my decision-making process is the aspect of classical rhetoric called ethos--the credibility of the person making the argument. If some guy tells me something about deco theory because he thinks that was what he was told in his OW certification class last week, I am not going to give that argument a lot of credit. When I see someone who appears to be clinging doggedly to a position with a closed mind, I am similarly unimpressed.

So, speaking for others like me, we will be convinced by what I described above. We really do want to know what is the best way to dive, and we are all hoping to see intelligent discussion in this and other threads.

 

[tomfcrist]

Um, no. You're questioning whether 'deep stops=more DCS risk' has been shown to your satisfaction by a particular study. That's a very different animal than asserting that 'deep stops=more DCS risk' is absolutely not true.

Have you seen that the designer of the studyreadily admits that there is no reasonable expectation for increased DCS incidence on your average tech dive even in light of his findings in this study?

The title of the thread is deep stops increases DCS.... That is just not supported by the findings of the study.

I think what is truly funny is that the same folks that come in here with good intentions to somehow defend their buddy, aren't even arguing the same point their buddy is. I would venture to say that if he was asked his opinion on which deco schedule to run, his choices being the shallow stop version from this study or the us navy dive tables he would choose the latter. In reality though, he would choose whatever algorithm he has personal faith in...probably not either of the options presented.

 

[Rich Keller]

The bottom line in this thread is that the indication is being made that deep stops will increase your risk for DCS. This is simply not true as it applies to technical diving.

Are you under the mistaken impression that the laws of physics apply differently to tech divers vs US Navy divers? Or are you under the mistaken impression that tech divers know more then the people who spend thousands of hours underwater every year testing these theories? Or are you under the mistaken impression that you are just smarter then everyone else? I would be interested in know what delusion you are operating under.

 

[Michael Guerrero]

Originally Posted by tomfcrist

Are deep stops effective if used properly? Absolutely, show me one piece of evidence to the contrary.

Well there is the study you're trying unsuccessfully to discount...

And the two French Navy studies cited earlier .

 

[Akimbo]

Has anyone developed a precise definition of what deep stops are? There are an awful lot variables including depth, time, diluent gas(es), PPO2, and relative depths of the first stops.

 

[Michael Guerrero]

However I can assume you can do basic division...hell I bet there is a calculator laying around you can use.

Take 10 random dive buddys, and find out how many times they have been bent collectively. Divide that by their collective dive count(just deco).....I'll bet it's less than 3.4%...

Tom, another thing you're missing here is that you're attributing the 3.4% DCS incidence with the NEDU study, which it is not. That is the result from the Heliox study I posted earlier. This is probably my fault since I know you read the study and are intimately familiar with it.

And since I know that YOU read the NEDU study, I'll post these numbers that you already know and are very familiar with but that the rest of these dummies I'm sure don't. The incidence of DCS for the shallow stop profile in the NEDU study was 3/192 (1.6%) and deep stops was 11/198 (5.6%). Again Tom, I know you already knew these numbers and really meant to cite them when you were typing 3.4% so many times above, so I wanted to bring the rest of these idiots, who clearly don't understand how science works and how to do decompression, into the discussion.

Carry on...

---------- Post added December 22nd, 2014 at 06:31 PM ----------

Has anyone developed a precise definition of what deep stops are? There are an awful lot variables including depth, time, diluent gas(es), PPO2, and relative depths of the first stops.

There have been several places where the researchers have tried to lend some clarity to the discussion, because "deep" stops can be one of two things normally.

First, you can consider a stop "deep" when it is performed deeper than that prescribed by your algorithm. So doing a Pyle stop on your way to your first Buhlmann deco stop can be considered a "deep" stop.

The other is the clear difference between the depth of the first stop in a bubble model as compared to a dissolved-gas model. This is the "deep" stop that most of the research has explored because researchers are trying to see if bubble models are more effective at preventing DCS than dissolved-gas ones.

---------- Post added December 22nd, 2014 at 07:02 PM ----------

Have you seen that the designer of the studyreadily admits that there is no reasonable expectation for increased DCS incidence on your average tech dive even in light of his findings in this study?

I just don't understand how you conflate all these things that don't pertain to one another and try and pass it off as some coherent understanding of decompression.

The NEDU study compared dive profiles with differing distributions of their decompression stops based on the algorithms used to determine those profiles, and not some arbitrary pattern devised by the researchers, as you've tried to assert--impugning their credentials in the process. The algorithms were given the bottom time and dive duration, and were run to produce the optimum distribution of stops based on the underlying models of the algorithms (namely bubble vs. dissolved-gas). One model, the bubble model, produced decompression stops that started significantly deeper than the other, dissolved-gas, model. One model, the bubble model, produced a statistically significant, higher incidence of actual DCS in divers, 5.6%, than the other, dissolved-gas, model at 1.6%.

Having said that, these were air decompression dives, which means the only thing they breathed the entire dive was air (20% O2, 78% N2, 0.9% Argon). The reason the results of this study may not significantly impact incidence of DCS in the tech diving community has nothing to do with the veracity of the study or results, nor the disputations of vocal critics, and everything to do with the use of increased concentrations of oxygen in decompression gasses as a means to accelerate inert gas washout. Period.

 

[tomfcrist]

However I can assume you can do basic division...hell I bet there is a calculator laying around you can use.

Take 10 random dive buddys, and find out how many times they have been bent collectively. Divide that by their collective dive count(just deco).....I'll bet it's less than 3.4%...

Tom, another thing you're missing here is that you're attributing the 3.4% DCS incidence with the NEDU study, which it is not. That is the result from the Heliox study I posted earlier. This is probably my fault since I know you ready the study and are intimately familiar with it.

And since I know that YOU read the NEDU study, I'll post these numbers that you already know and are very familiar with but that the rest of these dummies I'm sure don't. The incidence of DCS for the shallow stop profile in the NEDU study was 3/192 (1.5%) and deep stops was 11/198 (5.6%). Again Tom, I know you already knew these numbers and really meant to cite them when you were typing 3.4% so many times above, so I wanted to bring the rest of these idiots, who clearly don't understand how science works and how to do decompression, into the discussion.

Carry on...

---------- Post added December 22nd, 2014 at 06:31 PM ----------

Has anyone developed a precise definition of what deep stops are? There are an awful lot variables including depth, time, diluent gas(es), PPO2, and relative depths of the first stops.

There have been several places where the researchers have tried to lend some clarity to the discussion, because "deep" stops can be one of two things normally.

First, you can consider a stop "deep" when it is performed deeper than that prescribed by your algorithm. So doing a Pyle stop on your way to your first Buhlmann deco stop can be considered a "deep" stop.

The other is the clear difference between the depth of the first stop in a bubble model as compared to a dissolved-gas model. This is the "deep" stop that most of the research has explored because researchers are trying to see if bubble models are more effective at preventing DCS than dissolved-gas ones.

MG,

I love arrogant sarcasm...keep it coming, it makes you look like GI3's internet persona(that means a dick in case you are unfamiliar)...

Yeah I have read the studies, and yes you are correct that for some reason 3.4 stuck in my head. If you recall, I specifically called out the 1.5 of the dissolved gas model in an earlier post as well. Either way, 3.5% or 5.6% is not an accurate representation of the DCS rate on dives that just about any of us here are doing.

As far as the definition of deep stops, you can also consider any dive on a dissolved gas model that is not running 100/100 a deep stop model.

Make it easy on yourselves, go find Doolette, and BRW and ask them directly if this study means that deep stop profiles will statistically increase your DCS risk on a technical or recreational dive(assuming you are using one of the existing readily accessible models).

My opinion is that it's easier to get bent jacking around with gradient factors than it is to run straight RGBM. On second thought leave BRW out of the equation since RGBM is his baby.

The bottom line in this thread is that the indication is being made that deep stops will increase your risk for DCS. This is simply not true as it applies to technical diving.

Are you under the mistaken impression that the laws of physics apply differently to tech divers vs US Navy divers? Or are you under the mistaken impression that tech divers know more then the people who spend thousands of hours underwater every year testing these theories? Or are you under the mistaken impression that you are just smarter then everyone else? I would be interested in know what delusion you are operating under.

Rich, for gods sake...the navy doesn't dive this model in the way it was done in the study. Did they do it for the sake of experimentation?? Of course.

Y'all are some dense characters. You act like the profiles they dive here are in any way normal....for anyone.

 

[Michael Guerrero]

Sorry Tom, just taking a page out of your book. I assumed it was sarcasm since anything else is idiocy given the amount of discussion on the various boards.

You obviously haven't read the study.

If I was GI3 I would have called you a stroke...boom! Nailed it!

 

[Dr Simon Mitchell]

Make it easy on yourselves, go find Doolette, and BRW and ask them directly if this study means that deep stop profiles will statistically increase your DCS risk on a technical or recreational dive(assuming you are using one of the existing readily accessible models).

Tom,

You are missing the point. Of course it is possible to complete safe decompressions using any of the commonly available models, and yes, it would be difficult demonstrating significant difference in risk between any two algorithms in real world diving; there are just too many variables - including how the algorithm is applied. The question addressed by the NEDU study was which approach is more efficient. Thus, if you have two profiles that are conducted in identical manner (as described in my previous post) other than the distribution of stop depths, which one results in the least DCS? In the NEDU study the deep stops approach appeared less efficient which probably also means that if you do keep all other factors equal, a deep stops algorithm may be less safe. But this does not mean that a deep stops algorithm cannot be used to perform safe dives. I think this is the message David is trying to convey, and you are misquoting him to some extent.

I think what is truly funny is that the same folks that come in here with good intentions to somehow defend their buddy, aren't even arguing the same point their buddy is.

I can assure you that my views are very confluent with David's.

Tom, I did not come on here to get involved in another debate about deep stops. All of the points you have raised have been addressed in detail on other forums; particularly the RBW deep stops thread that others have linked to. If you really are interested in understanding this subject more completely, then your time would be well invested in reading that thread. In particular, you will find many posts that address the likely relevance of the NEDU study to technical diving.

The perspective that the study is irrelevant because profiles don't look typical of those used in technical diving is simplistic in the extreme. The most plausible reason for relative failure of the NEDU deep stops profile has been investigated, and its potential relevance to the profiles we dive has been explained multiple times. One relevant post can be found here:

Decompression Profile Project - UTD Ratio Deco vs Bulhmann - Page 51

I do agree that the title of this thread is somewhat pejorative, and it would not have been my choice. We do not know what optimal decompression is, but there is a strong signal in the emerging scientific literature that there it may be disadvantageous to over-emphasize deep stops, especially if there is not a corresponding extension of shallow stops to manage slow tissue supersaturation. What, exactly, constitutes "over-emphasizing" is not certain, but it may extend to some profiles generated by current deep stop algorithms. This perspective is certainly a change from the prevalent data-free belief of a decade ago that deep stop approaches were superior.

Simon M