The anecdotal experiences from myself and a lot of friends are that the bubble models work within the parameters of REALLY SHORT bottom times, but that once you start going beyond a certain threshold they stop working...
NEDU Study
- Thread starter klausi
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LiteHedded
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PfcAJ
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Your day will come.
LiteHedded
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UWSojourner
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You anecdotal experience would align well with how VPM actually operates. See the discussion here and the links referenced.
Kevrumbo
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June 2013 on the wrecks at Bikini Atoll, it was after the fourth consecutive day of two deco dives with 20/20 Trimix and Air top-off on the prescribed deeper stops of the Ratio Deco method, when I started having a few latent indistinct musculoskeletal transitory aches & pains ("the niggles") in my limbs/joints. So again, as implied by the NEDU Study, there's that long time duration exposure of Slow Tissue Supersaturation -over consecutive days in my case- which finally resulted in the start of microbubble formation and/or an inflammatory response by day four. Also note that the bottom gases of 20/20 Trimix, and Air top-off on the repetitive dive had very high FN2, with bottom depths ranging from 24m to 63m and bottom times of 35 to 50 minutes on Open Circuit. Deco gases were Nitrox50 and Oxygen.
By end of consecutive dive day number eight and immediately upon surfacing, I developed acute classic pain only type 1 DCS Right Shoulder, resolved with elective IWR and with the liveaboard's (M/V Windward) multiplace Recompression Chamber standing by. My treating hyperbaric physician on that Bikini Expedition was none other than Simon Mitchell, so while Dr. Mitchell started my IV Drip [Plasmalyte w/ Caldolor (Ibuprofen)] after completing the long IWR profile, I got the big picture, real world "captive patient" reminder again on his presentation of the applied results of NEDU Study.
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Kevin, I need to point out..... You did Ratio Deco methods..... You did not use VPM-B, and you did not employ bubble model theory. You did not strictly follow the basic gas kinetics formula. There is no connection between this incident and the nedu test.
You followed your advanced DIR classroom theories, where it has been a practice to override basic formula, to invent new reasons to diverge from the baseline, and to add different stops in different places. You used this over a multi-day heavy diving schedule.
That's what got you in trouble... Not bubble models, not VPM-B.
*****
I fully agree with your remarks that there is a need for extra caution over multi-day big diving. There is a residual lingering stress effect, and a multi-day depletion of energy and fluids, that cannot be modeled or accounted for in math. Like all physical activity, there are limits on endurance, stamina and the need for rest and recuperation.
This multi-day condition is one of many where smart dive planning procedure and practices and training, is needed to modify the dive plan.
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Kevrumbo
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Uh Ross,
No disrespect . . .but Simon Mitchell was my treating Physician for my type 1 DCS injury in Bikini Atoll June 2013, and witnessed all my dives up to Day Eight when the injury occurred --not you Ross.
I understand now and fully accept his diagnosis and the implied pathogenic etiology of Slow Tissue Supersaturation that he described with regard to the NEDU Deep Stops Study in a lecture presentation given during the trip. (My only profound regret over the whole incident was for both causing unnecessary worry for Dr. Mitchell by electing to choose IWR against medical advice of using the shipboard Recompression Chamber instead, as well as not telling him earlier about the "niggles" starting on Day Four).
The use of high FN2 bottom gases like 20/20 Trimix and Deep Air on Open Circuit, multiple mandatory deco dives per day over several consecutive days of a week or more; and doing two or more such "Expedition Trips" per year for the past six years: that's what really got me in trouble. I think my body's inflammatory response has reached its "deco stress tolerance", an inevitability that would have happened anyway in my experience & in my opinion whether using Ratio Deco or VPM-B or even Buhlmann ZHL-16 GF's implementation over such a career, along with just plain aging & physically getting out of fitness.
Doesn't necessarily mean this will happen to everyone over time, but then again it's something to be aware of if a pattern of post-dive "DCS symptomatology" -either vague or acute- arises from a previously routine deco profile with formerly benign post-dive results.
And that's the practical dilemma for the traveling tech diver on multi-day/multi-week overseas expedition trips --an individual trial & error experience on how much extra deco stress your tissues can take versus O2/CNS exposure limits with extended Oxygen profile times to clean up those tissues as needed --or worse-- with Oxygen in an IWR contingency because of acute DCS.
Those are real ethical & vital issues Ross -perhaps you and Simon can at least find common ground on that and discuss it here.
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Michael Guerrero
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Phew...it looks like we dodged a bullet there.
To the OP, your initial post makes me think you misunderstood the results of the study as they relate to the various types of decompression models in use, why the parameters were what they were, and why this makes them relevant to diving in general.
As was said above, provocative parameters were used deliberately to achieve a measurable, meaningful DCS outcome--that's why it doesn't resemble your normal diving. In other words, the designed outcome of the NEDU profiles was to bend divers. I assume getting bent is not the designed outcome of your dive profiles. Further, all models in use compute dissolved gas. Some do additional math to account for bubble sizes based on the assumption that bubble size is a critical factor to be controlled for safe outcomes.
We do know that your body can sustain bubble formation at some level without apparently immediate, adverse effects. Doppler studies have shown that every dive, to include recreational ones, produces some level of bubbling. What seems evident is that the assumption that bubble formation is equally bad at every phase of a dive, and therefore should be controlled aggressively, is not the right model for our physiology. The study also showed that models that purport to control for bubble size, through the use of deep stops, actually cause significantly more bubbling, as identified through Doppler readings (presumably due to increased slow-tissue on-gassing, as identified by the heat maps).
In my opinion, that data should be compelling enough to drive you to reevaluate the slope and time distributions of your decompression curves to determine whether you are comfortable with them. If you do so, remember that decompression profiles represent an envelope or range of likely safe outcomes, surrounded by regions of likely unsafe outcomes. The closer we get to the limits of the models, the harder it is to know where the line between safe and unsafe is. Also keep in mind that safe and optimum can be significantly different.
To the OP, your initial post makes me think you misunderstood the results of the study as they relate to the various types of decompression models in use, why the parameters were what they were, and why this makes them relevant to diving in general.
As was said above, provocative parameters were used deliberately to achieve a measurable, meaningful DCS outcome--that's why it doesn't resemble your normal diving. In other words, the designed outcome of the NEDU profiles was to bend divers. I assume getting bent is not the designed outcome of your dive profiles. Further, all models in use compute dissolved gas. Some do additional math to account for bubble sizes based on the assumption that bubble size is a critical factor to be controlled for safe outcomes.
We do know that your body can sustain bubble formation at some level without apparently immediate, adverse effects. Doppler studies have shown that every dive, to include recreational ones, produces some level of bubbling. What seems evident is that the assumption that bubble formation is equally bad at every phase of a dive, and therefore should be controlled aggressively, is not the right model for our physiology. The study also showed that models that purport to control for bubble size, through the use of deep stops, actually cause significantly more bubbling, as identified through Doppler readings (presumably due to increased slow-tissue on-gassing, as identified by the heat maps).
In my opinion, that data should be compelling enough to drive you to reevaluate the slope and time distributions of your decompression curves to determine whether you are comfortable with them. If you do so, remember that decompression profiles represent an envelope or range of likely safe outcomes, surrounded by regions of likely unsafe outcomes. The closer we get to the limits of the models, the harder it is to know where the line between safe and unsafe is. Also keep in mind that safe and optimum can be significantly different.
Hi Kevin,
No, I was not there. But you and Simon have been touting this story as a deep stop failure, and an extension of the nedu test, when in fact its something very, very different.
Despite popular myth, there is not some hidden accumulation of slow tissue gas that creates this multi-day condition. If you are in the water 4 times a day doing 2 hour dives, its still only 6 or 8 hours in 24 hours, (20 min total deep time and 4+ hours shallow time). Its not enough to carry over any significant gas volume. Yes, the computed deco time goes up a little bit, but not by much. This notion that a few minutes of deep stops was the problem all on its own, is pure baloney and nonsense. Your suggestion that some Slow Tissue Supersaturation is the cause is just plain silly in this situation.
Your full description here is one of accumulated multi-day fatigue, where you "reached your bodies limit", and exceeded it. It is not a model failure. Its a failure of the person to follow the experience and wisdom that predicted the very occurrence.
The wisdom that you have come to realize here - is to take it easy on multi-day dives. This multi-day issue and wisdom, existed long before DIR, RD, VPM and any other deeper stop approach existed. The multi-day problem is one that affects us all, and occurs regardless of the model used.
In my opinion, The conditions here is that your body gets fatigued and exhausted over many days of big diving, and it does not perform the on/off gassing as expected, compared to when you started out on day one. If you choose to deco close to the edge, day after day, then any minor variation in your bodies response, puts you over the edge. And the result is usually a big hit, because your body is in a fatigued or weakened state when it occurs.
******
This was not a deep stop problem, This is not a VPM-B problem. This is not a bubble model theory problem. The nedu test is not relevant to any of this. This is a multi-day dive fatigue issue.
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