Deep Stops Increases DCS

[Kevrumbo]

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Multiple deep deco on yo mama too Holmes. . .

 

[tomfcrist]

Please tell me it'll be the UTD-"modified" JJ

certainly won't be the Gue version

Not to rehash old stuff, but does Gue offering a JJ course change this jab into a bit of crow to eat?

 

[Dr Simon Mitchell]

An anecdotal account (and pure speculation of an incident last Nov 2014 to a diver at Blue Lagoon Dive-Ops Truk) --Vestibular/Inner Ear DCS symptoms as a result of not performing Deep Stops, or ascending too fast to the first intermediate deco stop. Again, along with the risk of type II Neuro DCS, you should take this into account when deciding to omit Deep Stops: are you willing to risk a rare but possible Inner Ear or type II DCS hit for the sake of not late supersaturating/loading your Slow Tissues???

Hello Kev,

You cannot draw any conclusions about causation of inner ear DCS without first knowing whether the diver has a large PFO. Over 90% of IEDCS cases have a large spontaneous shunt and the only profile that will be protective in the presence of a large shunt will be one that reduces the formation of venous inert gas bubbles (that might cross the PFO and be carried to the inner ear). There is now a significant body of data that show deep stop decompression diving profiles do NOT reduce venous bubble formation. Quite the opposite actually. Do you know whether that diver had a PFO?, because the data overwhelmingly suggest that was most likely the cause; not the presence or absence of deep stops. In respect of your comments about "Type II" (neurological) DCS (other than inner ear), there is no reason to believe that deep stops are specifically protective against such events, and as UWSojourner has pointed out, the NEDU study suggested the opposite.

The best most prudent compromise to practically apply from the NEDU Study & discussion, is to do the Deep Stops, and extend out the O2 profile at 6m such that you have a surfacing Gradient Factor of 60% or less (per the readout of a Petrel Computer upon surfacing from your O2 deco stop) --to ensure inert gas elimination from those Slow Tissues. This is especially warranted if you're doing multiple deco dives per day for a week or more -and I would also recommend taking a day-off/break after three consecutive days of multiple deep deco dives per day. . .

I would agree that this is a workable compromise. Deep stops can be safely incorporated into a dive profile if you want to use them. However, there is no evidence that you gain anything by doing so, and the available evidence suggests that their use is not the most efficient use of deco time. Thus, if you have a fixed amount of decompression time, the decompression will become less safe if you over-emphasize deep stops.

Simon M

 

[Ayisha]

Dr Mitchell, we really appreciate you coming on here and clarifying the information for us. Thanks so much for your patient responses!

 

[boulderjohn]

Dr Mitchell, we really appreciate you coming on here and clarifying the information for us. Thanks so much for your patient responses!

I agree. Your presence has made this thread far more valuable and informative then it would have otherwise been.

 

[Kevrumbo]

Hello Kev,

You cannot draw any conclusions about causation of inner ear DCS without first knowing whether the diver has a large PFO. Over 90% of IEDCS cases have a large spontaneous shunt and the only profile that will be protective in the presence of a large shunt will be one that reduces the formation of venous inert gas bubbles (that might cross the PFO and be carried to the inner ear). There is now a significant body of data that show deep stop decompression diving profiles do NOT reduce venous bubble formation. Quite the opposite actually. Do you know whether that diver had a PFO?, because the data overwhelmingly suggest that was most likely the cause; not the presence or absence of deep stops. In respect of your comments about "Type II" (neurological) DCS (other than inner ear), there is no reason to believe that deep stops are specifically protective against such events, and as UWSojourner has pointed out, the NEDU study suggested the opposite.



I would agree that this is a workable compromise. Deep stops can be safely incorporated into a dive profile if you want to use them. However, there is no evidence that you gain anything by doing so, and the available evidence suggests that their use is not the most efficient use of deco time. Thus, if you have a fixed amount of decompression time, the decompression will become less safe if you over-emphasize deep stops.

Simon M

Simon, I'm simply not willing to risk bubble nucleation & formation in my Fast Tissues for the sake of not loading/supersaturating my Slow Tissues later on in the deco profile (per indication of those "heat maps" by UW Sojourner); essentially a "Robbing Peter to pay Paul" dilemma.

And yes, I have plenty of time and an 11L Alu full of O2 to clean-up those Slow Tissues. . .

 

[Ayisha]

Simon, I'm simply not willing to risk bubble nucleation & formation in my Fast Tissues for the sake of not loading/supersaturating my Slow Tissues later on in the deco profile; essentially "Robbing Peter to pay Paul" dilemma.

And yes, I have plenty of time and an 11L Alu full of O2 to clean-up those Slow Tissues. . .

So, you do a minute or two deep stop. No harm, no foul. As long as your last shallow stop is extended, it should be better than what you've been doing thus far, right?

 

[victorzamora]

Buhlmann GF's to any arbitrary Lo/Hi value you want (i.g. 30/80 per AG's latest experimental test paradigm versus RD;

Just to clarify, this is NOT what AG used. He used something similar to 30/80 plus arbitrary deep stops because diving without deep stops is "way too dangerous." That attitude infuriates me beyond belief fir afew reasons:
1) A HUGE portion of the tech community is going away from deep stops and claiming they feel better. Clearly low gf of 30 isn't that dangerous. 2) He is testing a scientific principle in the least scientific manner possible... by ruining the chances of the one that will prove him wrong.
3) Why does he think his arbitrary addition of deep stops is an improvement despite the findings of the world's leading deco experts?
4) Many deep Trimix divers, including some of the world's leading deco experts are diving 40/70 and 50/70 and even just nitrox divers are using 30/70 due to gf high of 80 being too aggressive. Why use 30/80 PLUS deep stops (which would make it worse and more aggressive) if you're being honest?

I could go on and on, but it's a poor comparison and shows me that it's not an agency or a leader I have any interest in following.

 

[Kevrumbo]

So, you do a minute or two deep stop. No harm, no foul. As long as your last shallow stop is extended, it should be better than what you've been doing thus far, right?

I would continue doing Deep Stops -with the caveat impressions of the NEDU Study and attending Expedition Physician/Hyperbaric Specialist Dr. Simon Mitchell noted (and definitely not the histrionics of Vic Zamora above)- along with the extended O2 Profiles with my Truk Dive Guides. For the upcoming return trip to Truk 18Jan - 08Feb, I might take a break dive-day-off after three consecutive days of deco dives, or maybe elect to only do one deco dive per day and take a day-off at the end of a week.

 

[nadwidny]

I would continue doing Deep Stops -with the caveat impressions of the NEDU Study and attending Expedition Physician/Hyperbaric Specialist Dr. Simon Mitchell noted (and definitely not the histrionics of Vic Zamora above)- along with the extended O2 Profiles with my Truk Dive Guides. For the upcoming return trip to Truk 18Jan - 08Feb, I might take a break dive-day-off after three consecutive days of deco dives, or maybe elect to only do one deco dive per day and take a day-off at the end of a week.

I'm seeing a post here on Feb 9 from Kevbimbo- "Just got back from Truk (because if y'all don't know already I go there once in a while)...got bent. But man do I know deco.".