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Skin bends...

Discussion in 'Ask Dr. Decompression' started by Pebbles Photo, May 13, 2019.

  1. Storker

    Storker Divemaster

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    My apologies again, but you were the one who brought up the politician. I'm still somewhat curious as to which politician you were referring to. If it's irrelevant to the topic I'm quite happy to drop the issue, but personally I'd appreciate a clarification before we dropped the issue.
     
  2. uncfnp

    uncfnp Solo Diver

    # of Dives: 500 - 999
    Location: North Carolina
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  3. chillyinCanada

    chillyinCanada Solo Diver Staff Member

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    @Pebbles Photo, Putting aside the doppler for a minute, have you been able to tie any similarities of the dive profiles to the mottling or is the marbling/mottling just seem to be completely random?

    You have so many dives over so many years, it seems strange to me that this is just happening to you now. Have you been getting accompanying deep tissue pain?
     
    Blueringocto_73 likes this.
  4. Duke Dive Medicine

    Duke Dive Medicine Medical Moderator Staff Member

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    And Ron Nishi and company in Canada are pretty well-known. I know that Duke has done Doppler studies to measure bubbles coming from individual limbs, and bubbles increased when the limbs were moved. The subclavian veins may be central enough, and/or the tissues that they drain representative enough, that Dopplering one captures an accurate picture of what's going on in the venous system as a whole. I don't know that the same could be said for the internal jugular.

    Best regards,
    DDM
     
  5. Dr Simon Mitchell

    Dr Simon Mitchell Medical Moderator Staff Member

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    Hello Michael,

    In the neck there is the carotid artery taking blood to the brain, and the jugular vein draining blood from the brain. There is no "carotid vein".

    You cannot use either of these vessels as a valid indicator of decompression stress.

    The jugular vein is a poor choice because it is draining blood selectively from the fastest organ in the body. The brain is likely to be completely non-supersaturated (and not forming bubbles in its microvasculature) after any vaguely normal ascent whereas other slower tissue around the body may be supersaturated and bubbling significantly. I would not rule out the possibility that decompression bubbles can be detected in the jugular vein, but because it selectively represents such a fast tissue, it is not representative of what is going on in the body as a whole.

    The carotid artery is a poor choice because there will only be bubbles there if the diver is bubbling significantly in the venous system and there is a right to left shunt that allows the bubbles to get into the arterial circulation. This can happen of course, and bubbles are readily detectable in the carotid artery, but it would not be surprising to have grade 4 bubbles in the right heart (on the venous side) and hear nothing in the carotid artery in the absence of a PFO or pulmonary shunt.

    I think this is essence of DDM's message also.

    Simon M
     
    couv and Duke Dive Medicine like this.
  6. michael-fisch

    michael-fisch Manta Ray

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    Simon, I'm sure that you are right, but many German and other european tech divers, have been doing it this way for the last 20 years with great success ever since Buchaly and Waldbrenner pioneered the method back in the EKPP.
    What works - works.

    Michael
     
  7. Dr Simon Mitchell

    Dr Simon Mitchell Medical Moderator Staff Member

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    Hello Michael,

    With all due respect to Reinhard and Michael, you can't claim anyone has been doing this "with great success". They may have convinced themselves that they were doing something meaningful or that it "works", but some very basic physiological facts (see my post above) deem monitoring the large vessels in the neck to be an inappropriate measure of decompression stress. No one in the scientific community does it for that purpose, despite the fact that the neck vessels are extremely easy to isonate (as you point out), and there is no published evidence that it is a valid approach to adjusting decompression strategies.

    This issue would not be the only time that claims like "many divers have been doing it this way for the last 20 years with great success" have been ill-founded (eg the recent changes to UTD-RD after a comparative study). In relation to Doppler monitoring of the neck vessels, what may appear to work almost certainly does not work; at least not optimally. In other words, there are better and more meaningful approaches, and on this thread in the Dr Decompression sub-forum divers should be able to expect information that informs optimal practice.

    Simon
     
  8. tech_diver

    tech_diver Dive Equipment Manufacturer

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    This question I haven't been clear on from the start of the discussion is, "it works at what specifically?"

    Is this to research post dive deco stress of different profiles?

    I think you mentioned in one post that this is used for diagnostics after a dive. This device is used to decide to send someone to a chamber?

    When a diver returns from a dive, you listen to his bloodstream, what happens next?
     
  9. michael-fisch

    michael-fisch Manta Ray

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    We used it in order to tell if the decompression performed was too aggressive - before the onset of DCS symptoms.
    Then we could get back in the water with a buddy and fresh O2 tanks for a while (actually not IWR but interrupted decompression:)), perform surface decompression with O2 and/or give the nearest chamber a heads up. If we decided that chamber treatment was imperitive we were able to start the whole transport process 15-30 minutes before onset of symptoms, also reducing the wasted time between arrival in a facility that can perform treatment and the closing of the chamber door.

    One of the major advantages, that no other doppler method has, is the ability to doppler while still wearing a fuctioning drysuit. The normally preferred method is the very best method for use in a clinical setting, ours can be performed while sitting down as soon as the hood is taken off, and has been shown over the years to be pretty effective, as we use it.

    Michael
     
  10. Dominik_E

    Dominik_E Nassau Grouper

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    I think it is very easy to convince oneself that what one is doing is working. Even more so in cases where what we are trying to avert (DCS) is very rare and the border between "healthy" and "minor problem" subjective. It is much much harder to come to a scientific conclusion. Nature however has taught humankind the hard lesson that convincing oneself nearly never is enough. The internet is full of divers that have done hundreds or thousands of dives without any incident, then they get a single hit, then they are desperate to "find the cause". If they search hard enough, they will find something. Sometimes they then get this something "fixed" and do another hundred dives without incident. What exactly does this prove? Just that DCS is rare, right?

    Dominik
     

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