PfcAJ
Contributor
What?
Ascent Rate from Safety Stop
- Thread starter Chesty
- Start date
Please register or login
Welcome to ScubaBoard, the world's largest scuba diving community. Registration is not required to read the forums, but we encourage you to join. Joining has its benefits and enables you to participate in the discussions.
Benefits of registering include
- Ability to post and comment on topics and discussions.
- A Free photo gallery to share your dive photos with the world.
- You can make this box go away
Hello AJ,
No its not. You are citing old dogma which basically reflects what people hypothesized deep stops would do. The weight of available evidence (and I'm not talking about the NEDU study here) suggests that this hypothesis was wrong; probably because prolonged supersaturation in slower tissues is a more important determinant of venous bubble formation than transient supersaturation in fast tissues. The emerging evidence that deep stops are not effective in reducing venous bubbles (and may actually increase them) was the motivation behind a deep stop afficionado on the RBW thread spending a lot of time trying to argue that venous bubbles don't matter.
Simon M
No its not. You are citing old dogma which basically reflects what people hypothesized deep stops would do. The weight of available evidence (and I'm not talking about the NEDU study here) suggests that this hypothesis was wrong; probably because prolonged supersaturation in slower tissues is a more important determinant of venous bubble formation than transient supersaturation in fast tissues. The emerging evidence that deep stops are not effective in reducing venous bubbles (and may actually increase them) was the motivation behind a deep stop afficionado on the RBW thread spending a lot of time trying to argue that venous bubbles don't matter.
Simon M
ajduplessis
Contributor
The weight of availble evidence? Where is this evidence? Remember we are not talking about the NEDU study.
Thanks for the IEDCS docs you send, I will work through them once I have a bit more time. I also appreciate your approach in responding to my questions
Can you please elaborate on "may actually increase", this is a bit confusing. Does it, or does it not? "May actually" is a out there sitting on the fence............
Thanks for the IEDCS docs you send, I will work through them once I have a bit more time. I also appreciate your approach in responding to my questions
Can you please elaborate on "may actually increase", this is a bit confusing. Does it, or does it not? "May actually" is a out there sitting on the fence............
Last edited:
Hello AJ,
Thanks. I think everyone is being constructive... for a diving forum anyway!.
To my knowledge, depending on what we mean by deep stops there are only 3 relevant published human studies which I will come to in a moment. There are two human studies that have looked at the effect on bubble formation of inserting a single deep safety stop in the ascent from a no-decompression dive. These studies found opposite results (one supported the deep stop and the other didn't), and in any event, I don't think that is what we are interested in in relation to decompression diving. There are 3 studies that report bubble counts after decompression dives involving deep stops. Two of these compare deep and shallow stop profiles, and one just reports counts after deep stop profiles. One of the comparative studies is the NEDU study, so we will ignore that for the sake of this discussion. That leaves two studies.
Blatteau et al ran decompression dives from 60m according to a French Navy shallow stop model, and compared this to several decompression protocols including deep stops. The deep stops either had no effect on post dive venous bubbles or made them worse. That is the only comparative study.
Ljubkovic et al ran a series of trimix dives to 65m with decompression according to VPM-B (conservatism not specified) and reported median bubble grades of 3 and 4 (the two highest grades) at all monitoring points after the dive. There were so many venous bubbles that a significant proportion of divers exhibited passage of these into the arterial circulation, even though most of them did not have a PFO.
That's it, that's the evidence (plus the NEDU study which is the strongest of all, but I "contracted" with you to leave it out of this particular discussion). None of it supports your hypothesis, and all of it hints at the opposite (which, of course, is consistent with the NEDU clinical outcome results so it all makes sense). You certainly would not call it definitive proof... which is exactly why I was cautious with my wording. But try to get your head around the fact that it is the only relevant evidence we have. I am always struck by the certainty with which the benefits of deep stops are advocated by supporters (as in your claim about venous bubbles), yet there has never been a demonstration of any sort of benefit in human studies of decompression, and now the emerging evidence is pointing "somewhere" in the opposite direction.
References:
Blatteau JE et al. Bubble incidence after staged decompression from 50 or 60m; effect of adding deep stops. Aviation Space and Environmental Medicine 2005;76:4909-2.
Ljubkovic M et al. High incidence of venous and arterial emboli at rest after trimix diving without protocol violations. Journal of Applied Physiology 2010;109:1670-4.
I am happy to send you these papers as well.
Simon M
Thanks. I think everyone is being constructive... for a diving forum anyway!.
To my knowledge, depending on what we mean by deep stops there are only 3 relevant published human studies which I will come to in a moment. There are two human studies that have looked at the effect on bubble formation of inserting a single deep safety stop in the ascent from a no-decompression dive. These studies found opposite results (one supported the deep stop and the other didn't), and in any event, I don't think that is what we are interested in in relation to decompression diving. There are 3 studies that report bubble counts after decompression dives involving deep stops. Two of these compare deep and shallow stop profiles, and one just reports counts after deep stop profiles. One of the comparative studies is the NEDU study, so we will ignore that for the sake of this discussion. That leaves two studies.
Blatteau et al ran decompression dives from 60m according to a French Navy shallow stop model, and compared this to several decompression protocols including deep stops. The deep stops either had no effect on post dive venous bubbles or made them worse. That is the only comparative study.
Ljubkovic et al ran a series of trimix dives to 65m with decompression according to VPM-B (conservatism not specified) and reported median bubble grades of 3 and 4 (the two highest grades) at all monitoring points after the dive. There were so many venous bubbles that a significant proportion of divers exhibited passage of these into the arterial circulation, even though most of them did not have a PFO.
That's it, that's the evidence (plus the NEDU study which is the strongest of all, but I "contracted" with you to leave it out of this particular discussion). None of it supports your hypothesis, and all of it hints at the opposite (which, of course, is consistent with the NEDU clinical outcome results so it all makes sense). You certainly would not call it definitive proof... which is exactly why I was cautious with my wording. But try to get your head around the fact that it is the only relevant evidence we have. I am always struck by the certainty with which the benefits of deep stops are advocated by supporters (as in your claim about venous bubbles), yet there has never been a demonstration of any sort of benefit in human studies of decompression, and now the emerging evidence is pointing "somewhere" in the opposite direction.
References:
Blatteau JE et al. Bubble incidence after staged decompression from 50 or 60m; effect of adding deep stops. Aviation Space and Environmental Medicine 2005;76:4909-2.
Ljubkovic M et al. High incidence of venous and arterial emboli at rest after trimix diving without protocol violations. Journal of Applied Physiology 2010;109:1670-4.
I am happy to send you these papers as well.
Simon M
ajduplessis
Contributor
Simon, once again thanks. I appreciate your sharing the referenced documents.
Some quick comment. You ask to exclude the NEDU study for this discsssion but then immediately reference it to strenghten your point. What I will take away from this is "You certainly would not call it definitive proof..."
Lastly, I made no claims to venous bubbles. I confirmed that "A slower ascent allows any formed venous bubbles to collect and be dissipated gradually by the lungs". Is this not true? I also said we dive a certain profile (VPM-B +2) without incident. I also made the observation that I dont see divers in my area moving away from VPM profiles, nor do they complain about niggles or report DCS incidents.
Some quick comment. You ask to exclude the NEDU study for this discsssion but then immediately reference it to strenghten your point. What I will take away from this is "You certainly would not call it definitive proof..."
Lastly, I made no claims to venous bubbles. I confirmed that "A slower ascent allows any formed venous bubbles to collect and be dissipated gradually by the lungs". Is this not true? I also said we dive a certain profile (VPM-B +2) without incident. I also made the observation that I dont see divers in my area moving away from VPM profiles, nor do they complain about niggles or report DCS incidents.
Similar threads
