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Author Topic: Diver's trim contributes to DCI  (Read 3842 times)

cloudberrie

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Diver's trim contributes to DCI
« on: 22 Jul 14, 00:21 »
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  • Was re-reading Jablonski's Getting Clear on the Basics: The Fundamentals of Technical Diving recently, and the following sentence caught my eye when the book was discussing contributing factors to decompression illness.

    "Horizontal position during decompression or safety stop results in an increased rate of gas elimination when compared to vertical divers whose bloodflows to the lungs are more uniform. In order to maximise decompression efficiency divers should maintain a horizontal position during the off-gasig phase."

    Am really curious to find out why the above happens? What happens in the body physiologically that causes this. Anyone out there who can chip in to explain the above phenomenon? :)
    The cure for everything is saltwater. Sweat, salt or seawater. SEAWATER!!

    BareBear

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    Re: Diver's trim contributes to DCI
    « Reply #1 on: 22 Jul 14, 09:21 »
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  • Is there a footnote or reference provided in the book that points to some research?

    If all else fails you can email him at jarrod@gue.com

    If I were to hazard a wild, uneducated guess, I would guess that it could be due to the heart pumping blood on a level plane when you are horizontal. Tissues would then be able to off gas more quickly as more blood passes through even tissues further away from the heart.

    Cf a vertical diver, blood needs to be pumped against gravity for all areas/tissue above the heart.
    « Last Edit: 22 Jul 14, 09:29 by BareBear »

    limk

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    Re: Diver's trim contributes to DCI
    « Reply #2 on: 22 Jul 14, 10:45 »
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  • i don't deny there are differences, but have some doubts the differences are that significant.
    it's like saying yellow fins have a higher chance of triggerfish biting than scubapro jetfin
    oh btw jetfins u can buy at xxxxx. LOL.

    runez

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    Re: Diver's trim contributes to DCI
    « Reply #3 on: 22 Jul 14, 11:08 »
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  • IIRC, one theory is that in the horizontal position, all tissue compartments are at the same depth and at the same ATA, and therefore offgas at the rate predicted by the model. (Not sure if this is what the author meant, as he specifically mentioned the lungs only. Plus deco theory can bring about some lively debates...)

    In comparison, for a vertical position, some tissue compartments are at a higher ATA (deeper) than others, and thus may offgas slower than the model predicts. Since the model recommends the optimal depth for deco, these compartments below the optimal depth are not off-gassing optimally.

    I agree with limk, the difference may not matter. Being vertical is approx 0.15ata difference from head to toe.

    As a side note, deco theory also recommends a diver should be relaxed and comfortable during deco. So I think it's not that critical to be horizontal, especially if it adds noticeable stress to the diver. That may actually be worse off than being vertical.
    The Golden rule of diving - Any diver can call the dive. At any time. For any reason

    antacid

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    Re: Diver's trim contributes to DCI
    « Reply #4 on: 22 Jul 14, 13:59 »
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  • not to mention that some tissues offgas quicker than others. so maybe we should dive with our head and butt and the same level, then hands and feet at different levels. hahaha

    cloudberrie

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    Re: Diver's trim contributes to DCI
    « Reply #5 on: 22 Jul 14, 15:33 »
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  • there are no foot notes to this statement in the book, but seems to me both factor of gravity and all tissue being on the same level(thus pressure) sounds logical.

    Maybe i'll try emailing him like BareBear suggest. Let see if he replys! haha!
    The cure for everything is saltwater. Sweat, salt or seawater. SEAWATER!!

    BareBear

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    Re: Diver's trim contributes to DCI
    « Reply #6 on: 22 Jul 14, 16:17 »
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  • cloudberrie,
    Another idea - you could post this on DIR Explorers or other DIR specific forums. There are many GUE instructors who lurk there who could provide you a more accurate answer.

    I'm interested to know the answer as well.

    Did you get the e-book btw? How do you find it?

    snikrs

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    Re: Diver's trim contributes to DCI
    « Reply #7 on: 22 Jul 14, 17:18 »
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  • I've came across that and was questioning it as well. There's a short chatter about it on DIR-Explorers, but no conclusive results. http://www.direxplorers.com/dir-kit-questions/5106-deco-stop-trim-3.html

    Jaryl

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    Re: Diver's trim contributes to DCI
    « Reply #8 on: 22 Jul 14, 23:24 »
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  • Medically speaking, in terms of Physiology, it's due to a phenomenon known as Ventilation-Perfusion Mis-match (V-Q Mismatch).

    A small degree of V-Q mismatch is normal due to gravity and this is how the body functions.  (Humans are generally erect most of the time)

    Small theoretical improvement in gas diffusion potential if the whole lung is perfused and ventilated (more) equally while in a horizontal postion.  (there will still be a mis-match but this is over the anterior-posterior DEPTH of the lung v.s. the top-bottom LENGTH of the lung)

    But this is most likely insignificant.

    And yes, if it causes diver distress, causes poor buoyancy control leading to a bounces, probably more harmful than good.


    Cheers!
    Jaryl

    cloudberrie

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    Re: Diver's trim contributes to DCI
    « Reply #9 on: 29 Jul 14, 15:17 »
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  • Hi peops!

    just an update. Jarrod replied with regards to our queries on the statement in question. With his permission,

    "...the passage to which you refer is admittedly a bit theoretical but more or less reasonable. Because pressure differences are much more pronounced in water (due to density) a relatively small distance can establish more meaningful pressure differences which can affect blood flow and possibly negatively impact off gassing. Such an effect on DCS off gassing would be difficult to measure given the very low incidence of DCS but there is also very little reason to decompression in a vertical position so why take the chance?;-)"

    So i guess that's it then. we just have to wait and see if there will come further studies/researches in the future that could shed more light on this effect.

    Nonetheless, like he mentioned, in light of the other more tangible benefits it provides (e.g. better bouyancy management, better response to emergencies, or even better comfort for some), why decompress vertical if one is able to do it horizontally.  :D
    The cure for everything is saltwater. Sweat, salt or seawater. SEAWATER!!