Deep stops for recreational diving

[danvolker]

Morning Dan,



I'd be very interested to know how you are able to determine with such certainty that you've never approximated sustaining an incident of DCI.

Ok Doc, let's call this a "notion" of mine
The notion was something George was responsible for, as his concept was that with our very high VO2 max levels, we would clear very fast, and in the first hour after the dive, there would be radical changes to any bubbling that could occur from a dive where we had sustained any bubling. George's concept was to create a load of bubbles that could be easily off-gassed with the gradients, and filtered by lungs as well ( short version for brevity here)... O2 at 20 feet would typically have dramatic effects for this. When we had the first doppler studies on us, they had us do a 120 foot dive for 25 minutes on air, then do a 30 foot per minute ascent, and then surface with no stop...and then they hit each of us with the doppler....

The first time we did this, I was diving with a nearly separated shoulder, from a bicycle crash a week earlier. Still had major inflamation. Also, I was spearfishing on this dive, carrying a monster gun known as an Ultimate....it was a double barrel steel gun, that was like carrying a Nato Assault Riffle. It was my "weighting" for the dive....I carried it with the arm that was not effected by the bike crash.... I was expecting that there would be some bubbling after this kind of a stupid profile, on the injured shoulder area--with all the inflamation, I was expecting the blood flow to be impaired. In fact, that shoulder was clean, but the arm holding the gun was bubbling.....Each of us has some cascading in the first few minutes, and then it cleared quickly, and 20 minutes later each of us where looking very clean, according to the Doppler guy. This included even my gun arm

Part of George Irvine's thinking, was that if a couple of hours went by and we felt energetic and good, like we could go out and do a bike ride, then the likelihood was that there was no DCS..... But if we felt any sort of malaise, or tiredness, there was a chance that a sub-clinical hit was going on, but that it would likely resolve itself in the next 12 to 24 hours.

This is what I use to base my comment on about never having had a hit....I can't remember a time when I did not feel great after a dive, minutes later or hours later.

I did learn from that first doppler study, that we should never carry something heavy up on an ascent, or even for a good portion of the bottom time, as too much muscle contraction can begin limiting blood flow, and on the ascent, the carrying the heavy gun...or the carrying of a heavy camera, means your arms don't get good blood flow.....and micro hits are possible.
From this, I convinced my girlfriend to get her camera clipped to her chest for ascent, so her arms and shoulders could get better blood flow...and this made MAJOR changes to how her arms would feel after diving.... In fact, I think famous photographers like Kathy Church, may have been getting micro hits in their elbows for many years, and this inflamation over time, caused them to become arthritic.

Trust me, I don't do stupid profiles like the first doppler profile we did...that was just for the science, and each of us ( George, me, Bill and 5 other WKPP's) all knew we were very fast off-gassers from having been following George's experimental tables for so long, and never being sorry we did

That would depend on what kind of deep stops are being done during recreational diving (the OP topic), wouldn't it?

But, I don't believe that a need for exponentially more gas is the case. For example, NAUI recommends that a deep stop should be done for recreational dives deeper than 40 feet, with a one-minute stop incorporated at half of a dive’s max depth, followed by a two-minute safety stop at the 15- to 20-foot level.

And Dr. Peter B. Bennet indicates that a "deep stop at half the depth for 2.5 minutes significantly reduces not only bubbles, but also the critical gas supersaturation in the 'fast' tissue compartments (like the spinal cord's 13.5 minutes) without increasing the 'slow' compartments usually related to limb pain."

Seems to me that the performance of these sorts of deep stops within recreational diving limits would require only trivially more gas.

Cheers,

DocVikingo

What I was getting at, is that many advenced divers now, doing 130 foot dives, will do a 90 foot stop, maybe a 60 foot stop, and all of the time that they are doing these deep stops, they use way more gas up breathing at that depth, than they would if they were doing a stop at 20 feet.

For the tech diver, doing a lot of deep stops uses up much more gas still, three minutes at 200 ( after a 280 foot dive) uses up a great deal more gas than this diver will be breathing during their stop at 50 feet deep.... With trimix, there is no getting around needing some deep stops...but with air or nitrox to 130, you can get to 30 feet fairly quickly without using much gas, and holding a stop at 20 feet for 10 minutes at 20 uses very little gas--whereas 20 minutes between 120 and 50 will use up a lot of gas....So suddenly divers are having to bring massive amounts of gas with them, and are heavily overloaded with tanks....and have huge drag in the currents, and move around like inflated puffer fish

 

[Duke Dive Medicine]

For the record Dan, I'm not looking for argument, though I think I'd learn a few things if I tried to argue with YOU. I think it helps to remember that the paper I linked was for certain recreational dive profiles. Nobody would advocate just tossing in an extra 50 foot stop on a planned decompression dive, whatever tables or computer you're using.

 

[scubadada]

I started this thread 2 1/2 years ago, interesting that it was recently resurrected. Do we really have more high quality evidence today in order to make strong recommendation regarding the routine use of deep stops in recreational diving?

 

[CandiveOz]

I realise this thread is very old but I basically have the same question. I was watching @Dr Simon Mitchell presentation on youtube; Decompression Controversies. Around minute 25:45 he explains that he is not discussing a single deep stop during an NDL dive but deep stops during a Techical dive. His friend, Frans Cronje, had conducted this single deep stop study but there were other studies which contradicted the results. I became interested in this study so I googled Frans Cronje and found the study; Effect of varying deep stop times and shallow stop times on precordial bubbles after dives to 25 msw (82 fsw). It is the same study which was posted by @Duke Dive Medicine in Post #8.

So my question is; what were the other studies which contradicted Cronje's study? Links to the actual documents or abstracts would be great!

Thanks

 

[Duke Dive Medicine]

Here's a link to the study done by the US Navy Experimental Diving Unit, courtesy Gene Hobbs and Rubicon Foundation.

Redistribution of decompression stop time from shallow to deep stops increases incidence of decompression sickness in air decompression dives

Best regards,
DDM

 

[boulderjohn]

I recently published an article summarizing research on decompression diving, written with significant help and support from Dr. Simon Mitchell. You can find it here. That article is for decompression diving only. For NDL (now often referred to as no stop) diving, things may be different. I am gathering evidence now for a follow-up article on NDL ascent theories.

When the deep stops philosophy for decompression diving arrived, it hit the ground running and took off. It was quickly accepted as truth, even though it had never been tested. Some people then took the logical step to say that if deep stops are good for decompression diving (which was not proven), then they are probably good for NDL diving as well.

There is a reasonable hypothesis there, but it requires testing to be sure. Some testing has been done, but from those I have seen, the results are few, mixed, and inconclusive.

Now that the use of deep stops in decompression diving has turned out to be not as good as previously thought, it is tempting to reverse the earlier hypothesis and conclude that if deep stops are not so good for decompression diving, they must not be good for NDL diving, either. As before, that tempting hypothesis still requires testing.

If you read the article Simon and I wrote linked above, you will see that it concludes with a great deal of uncertainty. It sure looks like the really deep stops that characterized the movement in the early days are not so good for you, but many of the people who believe that are moving away with caution. In the article, we give an example of a dive that would have a first stop at 150 feet for Ratio Deco or 120-130 feet for VPM, RGBM, or Bühlmann 20/80, which are all significantly deeper than a pure Bühlmann first stop at 60 feet. Many of the experts who are perceived as being anti-deep stop are using GFs that would give a first stop at 90 feet. That is nowhere near as deep as those other algorithms, but it is still deeper than pure Bühlmann.

The search for the best possible algorithm for decompression diving continues, and at this point in my studies it appears as if the same is true for NDL diving.

 

[CandiveOz]

@Duke Dive Medicine thank you for the link to NEDU study.

@boulderjohn congratulations on an outstanding article! You have brilliantly summarised all the latest thinking regarding deep stops during decompression diving. And I really appreciate that you documented all your sources. The Fraedrich Study really got me excited and after reading your article I ran to the State Library of NSW to see if they had a copy of the Journal. Unfortunately they didn’t but ordered an electronic copy of the study from the National Library in Canberra. Apparently it will take two weeks to get it. The internet is slow down here…

The reason why I was particularly interested in the Fraedrich Study was the gradient factors they considered acceptable seem to be in line with my own personal views. I started a thread to gain a consensus as to appropriate gradient factor (GF) presets and defaults for dive computers. My concern is that divers buying a GF computer may just leave the computer on its default preset GF thinking that the manufacturer has selected the most appropriate setting to use when in reality there is still debate surrounding this issue.
Gradient Factor Presets by Manufacturer/Computer

But getting back to my original question in this post, if you are gathering evidence for a follow-up article on NDL ascent theories, then I expect you will be addressing the single 1 – 2 min deep stop during an NDL dive. And since you are in contact with Simon, maybe you can ask him about the studies that contradict Cronje’s. I’m looking forward to your next article. Great work!

 

[boulderjohn]

@Duke Dive Medicine

But getting back to my original question in this post, if you are gathering evidence for a follow-up article on NDL ascent theories, then I expect you will be addressing the single 1 – 2 min deep stop during an NDL dive. And since you are in contact with Simon, maybe you can ask him about the studies that contradict Cronje’s. I’m looking forward to your next article. Great work!

I am working on that stuff--getting information from the people who do add deep stops as to the reasoning behind it.

There is a much bigger difference between NDL dives and decompression dives than one might think, and there really isn't a lot of research on the effects of deeper stops. To me, the big difference is that in NDL diving, there is a huge range of dive depths and times where the accepted ascent strategy is exactly the same. Add 5 minutes to a 20 minute dive at 80 feet, and your ascent strategy is exactly the same. Add 5 minutes to a 20 minute dive at 300 feet, and you are dealing with a huge change in ascent profile.

If you begin an ascent within NDLs, and you decide to do a 2 minute stop half way up, you will still be within NDLs when you continue the ascent. Perhaps that is the reason people aren't falling all over themselves to do studies.

 

[Duke Dive Medicine]

@boulderjohn , great article!

 

[Compressor]

Thank you for the article.
Unfortunately, the problem of decompression is difficult to solve since human physiology as well as diving bubble stress is a dynamic process and subject to multiple changing variables. It makes it fascinating but also very challenging to model.