Deep Stops Increases DCS

[rossh]

Again, are you REALLY trying to tell me that VPM-B+3 is close to 40/70? I'm looking at two profiles right now and they aren't.
.

220 ft 40 mins.. .that's a big dive, and you had to go that far out, to make an appreciable difference. But come back a few steps towards more normal dives.... not much difference at all. Hence my point. VPM-B+3 is close to 40/70, most of the time.

One thing is for sure, no matter what : VPM-B+3 and 40/70 is much closer together, than 40/70 and its origin 100/100 ZHL model.

 

[PfcAJ]

220 ft 40 mins.. .that's a big dive, and you had to go that far out, to make an appreciable difference. But come back a few steps towards more normal dives.... not much difference at all. Hence my point. VPM-B+3 is close to 40/70, most of the time.

One thing is for sure, no matter what : VPM-B+3 and 40/70 is much closer together, than 40/70 and its origin 100/100 ZHL model.

220 for 40 isn't that wild. A bunch of folks are doing that.

Hell, 220 for 25 is something you can do in a tech 2 class. Lets do that one!! I like this game!

220', 25mins, 15/55 on the bottom, 50% and oxygen for deco.

VPM+3 stops you at (again) 150'
40/70 stops you at 120

Before 1st gas switch, VPM has 18mins of deco (crazy)
40/70 gives you 12mins
6mins difference BEFORE you're even on a deco gas. But wait, theres more!

VPM+3 gives you 31mins on oxygen
40/70 gives you 37mins.
That's a difference of 6 minutes on oxygen!

To recap, VPM adds 6mins of deep time and deletes 6mins of oxygen time. Terrible idea. Why on earth would you want to dillydally below your deco gas for an additional six minutes then turn around and ditch six minutes of time on oxygen?

Do you really want to do another?

Its a little funny to me that we ended up on 220' for 25mins. Both VPM+3 and 40/70 result in the same deco times, but one is distributed deeper. Suspiciously like the NEDU study.

 

[rossh]

Bubbles, irrespective of their location, come and go for the same reasons: they form to relieve gas supersaturation and they dissolve while the surrounding tissue has a lower gas partial pressures than inside the bubble. The Swan et al. paper I just cited and linked illustrates the time course of intravascular and extravascular microbubbles come and go at the same time.



No, we do not know exactly how DCS occurs, but the literature hypothesizes different manifestations of DCS as occurring from intravascular and extravascular bubbles. It is irrelevant that models of which you are aware are incomplete in this regard.



No, Simon suggested this was one origin of VGE. The literature I reviewed in my earlier post supports that point of view



No, DCS is thought to occur in both well- and poorly-perfused tissues, given appropriate conditions, that is why we have a range of compartment half-times in decompression algorithms. The VGE detected in the central venous blood arise from all the body tissues. Presumably those VGE which originate from extravascular tissue are those bubbles which formed adjacent to the capillaries. A poorly-perfused tissue has relatively fewer capillaries (not none).



The presence of bubbles either in the vasculature or in extravascular tissue does not inevitable lead to DCS. However, the more bubbles there are, the more likely they are to form at (extravascular) or impact (intravascular) a DCS-site.

The Swan study: they used pigs, but if they used humans, they skipped 2 1/2 hours of deco time..... So are those big bubbles truly representative of the tiny / almost non existent harmless ones we get in everyday diving? Probably not. Of course when one blows up the deco so grossly, everything appears at the same time.


Yes VGE has one origin - agreed. Are we playing semantics now?


"" Presumably those VGE which originate from extravascular tissue are those bubbles which formed adjacent to the capillaries.""


Exactly - that is the issue - you presume, based on what? Can you show us some science that clearly proves the connection.


So far we have deco tests with 2 hours of missed deco, or deliberate death, but they simply do not provide that info that we need. We need to see what happens when normal harmless deco occurs, with normal ordinary levels of VGE. So far .. nothing


>

 

[kensuf]

Hi.

I've really been avoiding this thread.

In January I did a long run in Cathedral. My dive buddy and I had a 200 minute bottom time at an average depth of 150'. I've been told by my dive buddies that I frequently run an aggressive deco, and on this dive there I did nothing different.

My partner on the dive was running VPM-B/E on +3 on a popular DC. When we got to our oxygen stop his computer claimed he had about 40 minutes less deco than me (I was running my standard "aggressive" deco).

On all of our other dives, he usually did more deco than me, so he decided to stay with me.

I'm not a decompression scientist, but my experience has been that on longer dives VPM produces significantly shorter shallow stops -- it seems to forget that the time I'm spending deeper I'm still on-gassing in my slow tissues. While it may work fine for short "bounce" dives, it really seems to get wonky when the dives are getting longer.

One of my dive buddies and I are planning a 300 minute bottom time at Cathedral within the next two months (anticipated run-time of about 10 hours), and I will not be trusting my body to VPM for that.

In my opinion, the best algorithm is the one that gets me out of the water without getting twisted, and I really have zero interest in hurting myself due to a faulty algorithm. Although ZHL16+GF's may not be the best thing in the world either, they're working for the dives my friends and I are doing, where VPM clearly doesn't.

Ross, Multi-Deco is a nifty piece of code, but I am struggling with recommending it to my students given your religious fanaticism for VPM. I have an AN/DP class coming up in two weeks and I'm currently evaluating a few other dive planning tools because of your constant proselytizing for VPM. You could have simply taken the high road and said "my tools support the common and popular decompression algorithms and you should make an educated decision on which model suits your diving" and been a winner.

MultiDeco 4.07 by Ross Hemingway,
ZHL code by Erik C. Baker.

Decompression model: ZHL16-B + GF

DIVE PLAN
Surface interval = 5 day 0 hr 0 min.
Elevation = 0ft
Conservatism = GF 40/85

Dec to 150ft (2) Diluent 20/30 1.00 SetPoint, 60ft/min descent.
Level 150ft 197:30 (200) Diluent 20/30 1.00 (1.11), 86ft ead, 94ft end
Asc to 120ft (201) Diluent 20/30 1.00 SetPoint, -30ft/min ascent.
Asc to 100ft (201) Diluent 32 1.30 SetPoint, -30ft/min ascent.
Stop at 100ft 1:20 (203) Diluent 32 1.30 SetPoint, 82ft ead
Stop at 90ft 5:00 (208) Diluent 32 1.30 SetPoint, 69ft ead
Stop at 80ft 8:00 (216) Diluent 32 1.30 SetPoint, 56ft ead
Stop at 70ft 10:00 (226) Diluent 32 1.30 SetPoint, 44ft ead
Stop at 60ft 15:00 (241) Diluent 32 1.30 SetPoint, 31ft ead
Stop at 50ft 20:00 (261) Diluent 32 1.30 SetPoint, 18ft ead
Stop at 40ft 28:00 (289) Diluent 32 1.30 SetPoint, 6ft ead
Stop at 30ft 39:00 (328) Diluent 32 1.30 SetPoint, 0ft ead
Stop at 20ft 52:00 (380) Oxygen 1.30 (1.60), 0ft ead
Stop at 10ft 102:00 (482) Oxygen 1.30 (1.30), 0ft ead
Surface (482) Oxygen -30ft/min ascent.

MultiDeco 4.07 by Ross Hemingway,
VPM code by Erik C. Baker.

Decompression model: VPM - B/E

DIVE PLAN
Surface interval = 5 day 0 hr 0 min.
Elevation = 0ft
Conservatism = + 3

Dec to 150ft (2) Diluent 20/30 1.00 SetPoint, 60ft/min descent.
Level 150ft 197:30 (200) Diluent 20/30 1.00 (1.11), 86ft ead, 94ft end
Asc to 120ft (201) Diluent 20/30 1.00 SetPoint, -30ft/min ascent.
Asc to 100ft (201) Diluent 32 1.30 SetPoint, -30ft/min ascent.
Stop at 100ft 0:20 (202) Diluent 32 1.30 SetPoint, 82ft ead
Stop at 90ft 3:00 (205) Diluent 32 1.30 SetPoint, 69ft ead
Stop at 80ft 6:00 (211) Diluent 32 1.30 SetPoint, 56ft ead
Stop at 70ft 9:00 (220) Diluent 32 1.30 SetPoint, 44ft ead
Stop at 60ft 12:00 (232) Diluent 32 1.30 SetPoint, 31ft ead
Stop at 50ft 18:00 (250) Diluent 32 1.30 SetPoint, 18ft ead
Stop at 40ft 25:00 (275) Diluent 32 1.30 SetPoint, 6ft ead
Stop at 30ft 34:00 (309) Diluent 32 1.30 SetPoint, 0ft ead
Stop at 20ft 48:00 (357) Oxygen 1.30 (1.60), 0ft ead
Stop at 10ft 89:00 (446) Oxygen 1.30 (1.30), 0ft ead
Surface (446) Oxygen -30ft/min ascent.

 

[David Doolette]

The Swan study: they used pigs, but if they used humans, they skipped 2 1/2 hours of deco time..... So are those big bubbles truly representative of the tiny / almost non existent harmless ones we get in everyday diving? Probably not. Of course when one blows up the deco so grossly, everything appears at the same time.
>

What no-stop time for 100 fsw are you presuming for a 20kg pig that performs a 45 minute oxygen prebreathe before descent and is anesthetized at depth? Hint: DCS susceptibility increases with body mass, oxygen prebreathe decrease decompression obligation, and work at depth increases decompression obligation.

 

[Dr Simon Mitchell]

This continued effort to incorrectly merge intra vascular and extra vascular bubbles together as one, and then plays tricks on the public about VGE, continues.It ignores the advise of experts that VGE are a secondary indicator only, that VGE do not predict DCS, and are at best a relative indicator only, that has to be applied cautiously.

All experts (including me) agree that the positive predictive value of VGE is not good enough to use VGE for diagnosis of DCS. If anyone is "playing tricks", it is you by pretending that this renders VGE pathophysiologically insignificant.

You repeat your attacks on VPM because it was used in a study to perform exactly as it was asked , and it it performed flawlessly.

It was used in a human study where it resulted in high grade VGE after almost every dive.

You quote a new animal study, where they drove the subjects to death with a direct ascent, found bubbles as expected post-mortem. But adds nothing to any of your points above. (8 ATA, 45 mins, direct ascent).

Did you actually read the study? You asked for evidence that VGE correlated with tissue bubbles. In this study the animals with VGE had high levels of tissue bubbling. The animals with low VGE had few or no tissue bubbles. There is your correlation published a month ago by a group you have indicated that you trust. I can't put it more simply than that. The decompression stress imposed on the animals is irrelevant, and parenthetically, it is often necessary to expose animals to much more provocative dives than humans in order to produce clinical DCS.

The key question now: Having based your defence of higher VGE grades after VPM dives on an imaginary separation between VGE and tissue bubbles, are you going to rethink the whole thing?

Simon M

 

[David Doolette]

"" Presumably those VGE which originate from extravascular tissue are those bubbles which formed adjacent to the capillaries.""


Exactly - that is the issue - you presume, based on what? Can you show us some science that clearly proves the connection.

>

Well, there is the photomicrograph of exactly that happening in post 1002 of this thread. Besides which it would be a bit silly to presume that those VGE which originate from extravascular tissue are those bubbles which formed furthest from the capillaries.

I only ask to illustrate the fallacy in your argument, but can you show us some science that clearly disproves a connection between extravascular and intravascular bubbles?

 

[Dr Simon Mitchell]

I meant to say this for a long time after reading a couple of threads on RBW and here.
After this long thread, I think it is time for me and I hope many of those reading and getting useful info, to thank Dr @Simon Mitchell and Dr @David Doolette.

They spend liberally their time with discussion well below their par, without gain just for our benefit and for the only reason they cannot stand to see misinformation spread in our community.

Simon, in fact you being a physician, are preventing harm to all of us providing better information and the current state of understanding on decompression. Please allow me a joke: in a sense you are a nut case you are undermining your customer base because if successful in better educating us you will prevent DCS!

Cheers and thanks to both of you .

First, thanks to you and the others who have made related comments. It is only fair to also acknowledge UWSOJOURNER who has contributed immensely to making the issue more understandable.

Second, the reason I do it is that I remember the days when I had no medical / scientific training and was a young diver, absolutely passionate about information related to the physiology of the sport. In those days we did not have the internet, and I used to buy every magazine and attend every talk I could. In the modern era I know that divers who are similar to me back then will be poring over the internet looking for their information. It is an imperfect medium but by and large, provided the conversation is kept civil as it is on this forum, discussions usually arrive at the correct conclusion. On that background, I have never seen such blatant misrepresentation of our body of knowledge (as it currently stands) in relation to a safety critical subject as I see in this discussion of approaches to decompression. Taking a stand against this is costly both in terms of time and (sometimes) stress levels. But when I self-reflect on the knowledge-thirsty diver I once was, I don't see that there is much choice. Unfortunately, being forced into these debates risks one being typecast as "pro-this" or "anti-that", and the debates seem much more polarised than they really are. One thing you can be sure of is that we are guided by the science.

Simon M

 

[fsardone]

... It is only fair to also acknowledge UWSOJOURNER who has contributed immensely to making the issue more understandable.

You are obviously correct!
UWSOJOURNER made a great contribution by developing the graphical representation of relative supersaturation and then having to defend explain and justify here and elsewhere ... not only that but all that came with it.

Cheers

 

[DavidFL]

It is only fair to also acknowledge UWSOJOURNER who has contributed immensely to making the issue more understandable.

Scubadada also called out UWSojourner

+1

Kevin's heat maps took some concentrated effort to comprehend, but once the 'aha' moment happened, they provide a way to try to keep in mind all the compartments in these discussions....when most of the other 2D graphics have to leave that out. It's especially important to this 'efficiency' and 'distribution of stops' material.