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Thread: Dive computers, deco and tissue compartments

  1. #21
    Guru HP's Avatar
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    deep stops while on-gassing are doing very little for your bubble reduction, even in the fast tissues and then take your time adding extra min's to the off gas stops...
    and

    Our studies and intelligent theorising has fudged beyond what is or is not safe dive practices...we'll never know...
    Aren't really terribly compatible with each other are they?

    Are you suggesting that dissolved gas decompression theory is proven beyond doubt?

    I was very, very reluctant to actually "nail my colours to the mast" with the original reply on this thread, because I would say that there are still way more unknowns than there are knowns.

    I think, at the very least, there is a strong body of evidence to suggest that some sort of bubble control is useful and effective in decompression.

    My own personal belief, in broad terms, is that decompression is all about bubble control

    I wouldn't necessarily expect others to adopt that same view
    "Some people could f**k up a baked potato..." Squeaky McTight / David Mamet

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  3. #22
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    Quote Originally Posted by RichW View Post
    So if you ascend to 50% of depth, all tissues would be off gassing?
    Depends how long you've been down there

  4. #23
    All we wanted was a home... Manics Blu DL's Avatar
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    A massively complex and spaghetti mess of a subject this one !!

    Slightly off topic q to those in the know...

    I was in Sharm recently and having done some nice easy rec diving 25m max over the week at 2 dives a day. Dive 8, A lady on the boat came up from a dive feeling dizzy when she put her head on one side. She was obviously not happy and after about 10-15 mins I told her to see the guide, as it may be a bend and she may require 02/treatment. She said she had dived well within tables / computer wasn't beeping / "couldn't have a bend" actually got quite stroppy with me!! - and would not accept when I said she could have dived to 15m for 30 mins and got a bend even when well within tables - sometimes it 'just happens'

    She carried on diving the following day even though I said to her again she should at least not dive until the dizziness has gone. She did the morning dive and got out with no dizziness and it didn't re-occur.

    My thoughts are that it was a left/right ear imbalance, but is it possible that the dive on 32nitrox to 20m could actually have solved the bend?
    Regards, ***All written without prejudice

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  6. #24
    TDI Instructor Trainer Mark Powell's Avatar
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    Quote Originally Posted by HP View Post
    Please feel free to pick holes in that / add your ten cents worth Mark - you're more of an authority on these things than I am.
    I thought your summary was excellent.

    The biggest problem with this whole topic is the lack of knowlede on many of these topics. I don't just mean by divers in general but by the real experts. The most knowledgeable researchers I spoke to when writting my book were also the ones that stressed the most strongly that we simply dont know enough about decompression to make definitive statements. Many of the experts would never make as definitive a statement as some of the ones already published on this thread.

    I cringe when I hear people saying that either dissolved gas models or bubble models are right or wrong. That's an overly simplistic view that gives a level of confidence that is just not warranted.

    None of the current decompression models really claims to be a complete description of what happens in the body when we dive. There are simply too many unknowns. Instead they are a way to try to do a dive without getting bent.

    Physiologially the dissolved gas theory has major faults, and yet Buhlmann tables have a great success rate. Bubble models were based on much less practical research and yet have some aspects which are considered more progressive.

    I'll defer to someone who knows much more about decompression than me.
    Quote Originally Posted by Richard Vann at the DAN Technical Diving conference 2008
    I’m not going to answer the questions that you want to have answered, nobody can.

    The question being, how can you reliably consistently decompress safely.

    Richard Vann PhD, Assistant Research Professor in Anesthesiology, Safety Officer and Director of Applied Research at Duke Hyperbaric Centre, Vice President of Research DAN
    Mark Powell
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    Deco For Divers by Mark Powell A divers guide to decompression theory and physiology
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  8. #25
    Nigel Hewitt nigelH's Avatar
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    Humm....
    When you come down to it we know lots about deco and have a century's worth of data to look back over.
    And one thing we know is that the problem with deco isn't dissolved gases, that's just physics, it the wretched divers.
    If we had one standard diver who stayed hydrated and warm and who we know didn't have any arterial shunts things would be a lot easier. If we knew what other factors to add to the list it would help.

    Producing a 'safe' profile for diver X is a problem with to many unknowns. My 'two computer and plenty of margin from their requirements' system seems to have worked for me for many years now but I can't promise more than an "I hope so" for my next dive and you don't even enter the analysis.

    That said, almost all the 'undeserved' bends I've seen have been dehydration but, as they say, the plural of 'anecdote' is not 'data'.
    nigelH
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  9. #26
    Guru HP's Avatar
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    the plural of 'anecdote' is not 'data'
    "Some people could f**k up a baked potato..." Squeaky McTight / David Mamet

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  10. #27
    TDI Instructor Trainer Mark Powell's Avatar
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    I agree Nigel, many of the other things are much more important than the fine details of the deco model.

    Simon Mitchell gave a fantastic talk at EuroTek.08 where he discussed things like hydration, exercise and temperature and showed that these have much more of an impact than the specifics of the deco model.
    Mark Powell
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  11. #28
    New Member jonny4846's Avatar
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    It is my point, just as Nigel and Mark had put it about the fine details of the deco model. Hydration, fitness and exposure are all areas yet to be explained as to how the specific model will be altered. These, as Mark points out are more important to understand than what we think we know about how are body is behaving in relation to a specific model.

    It's not searching for the precise mathamatical formula, if we can't input these variables. And Nigel, I dont think there is such a thing as an 'undeserved bend', IMHO, it's a bend with a reason unknown...

    Jonny

  12. #29
    Notice my avatar. I am hard astern. BJ's Avatar
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    Quote Originally Posted by Mark Powell View Post
    . The most knowledgeable researchers I spoke to when writting my book were ...
    Sorry, You just made me think of Ernie Wise!
    Author of Amazing Diving Stories (Wiley Nautical). Consistently the top-selling scuba diving book on Amazon.

  13. #30
    "Three sheds" Janos's Avatar
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    Quote Originally Posted by GLOC View Post
    But then I have a hole 7-8mm x 12mm in my heart and I have done quite a few deep dives in the region of 45-70m and only had one minor hit (visual disturbances only, no other symptoms); I subscribe to the deep stop theories!

    The problem is we do not know enough about this, especially the deeper trimix dives...

    I know what I will continue to do though.
    Taken on their own, I don't think that one divers dives give enough of a sample to draw a conclusion from either way. I certainly wouldn't accept a 1 in 10,000 chance of a serious neuro hit and I don't know many people who have done 10,000 dives.

    You need to look across many, many dives, which is why I don't subscribe to the "it works for me" attitude.

    Janos
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