Deep Stops Increases DCS

[rossh]

Are you saying that GF 100/100 is a better option than VPM?

For any given (fixed) deco time, where there's actual slow tissue saturation, yes. (so not a 5min bounce to 200ft with 15mins of deco)

But unfortunately there's incredible resistance to understanding that fixing the total deco time at X minutes was what made the NEDU study so powerful.

Hi,

Nowhere is it written, or shown, that all dives are some how made equal by matching up the total run times. It is done only as a convenience for testing procedures. Some researchers like to use this to an unfair advantage in comparison too, as its always biased toward the shallow profile.

There is a little bit too much weight been given to the value of surface stress. As successful deco procedure is controlled in the dive portion, and that is where the eventual dive outcome is determined.

If a higher stress in the surface portion passes without issue, then it never was an issue in the first place.

.

 

[Storker]

No wonder people feel like the process in going in circles - because it is.

You mean like the discussion in this thread?

By the way, back in post #1057 you claimed that "[VPM-B] used existing data as a basis, and a proper measure of decompression stress, to come to its own conclusions". I see now that you have later changed this to "The basis of decompression stress is supersaturation pressures, and this can be measured in a model independent way". It's still about measuring, though, even if you initially claimed that it was VPM-B that uses "a proper measure of decompression stress" (which easily can be interpreted as an implication that other models don't).

In any case, since you haven't bothered to answer my very simple question I'm still wondering how you measure decompression stress, particularly since ultrasound-detected microbubbles in the bloodstream are irrelevant. Care to educate me?

Also, in post #1078 you say

FACT: Mitchell and Doolette [...]have never publicly put the blame of those poor practices above, on where they originate. Instead they just blame it all on VPM-B and bundle all those problems on me.

And in post # 1089 I asked for a cite for that. Still waiting. It doesn't have to elaborate, the post # where Drs. Mitchel land Doolette "blame it all on VPM-B and bundle all those problems on me" is just fine.

 

[Storker]

Nowhere is it written, or shown, that all dives are some how made equal by matching up the total run times. It is done only as a convenience for testing procedures. Some researchers like to use this to an unfair advantage in comparison too, as its always biased toward the shallow profile.

So, are you saying that for a given run time, a deco schedule that emphasizes shallow stops over deep stops is better?
Or are you saying that for a given run time, the shallower dive carries a lower risk of DCS than a deeper dive?

 

[nadwidny]

Ah yes... real models vs GF... 40/ 70, no this time use 60/ 85, ....... no it looks better if we use 65/72..... You see... all this GF fudging to make your graph look perfect...... "My stretched out GF , tailor made, fitted to perfection GF fudge looks just perfect".

Reminds me of how VPM morphed into VPM-B to match the GFs that people were running 10 years ago because people were getting bent on VPM.

 

[rossh]

Reminds me of how VPM morphed into VPM-B to match the GFs that people were running 10 years ago because people were getting bent on VPM.

Oh what rubbish. VPM-B was released 16 months after original VPM-(A), becuase Eric Baker found issues with the way VPM-(A) worked. We could all see things were not correct with VPM-(A). And no, there was no growing pile of injuries either.

Added: And what you don't realize, was there was a version 2 V-Planner, that acted as a bridge between v1 and v3 with the final VPM-B. This modified v2 version was all patched together to give a B style plan, but it filled the gap OK. It came out in April 2002.

 

[rossh]

You mean like the discussion in this thread?

By the way, back in post #1057 you claimed that "[VPM-B] used existing data as a basis, and a proper measure of decompression stress, to come to its own conclusions". I see now that you have later changed this to "The basis of decompression stress is supersaturation pressures, and this can be measured in a model independent way". It's still about measuring, though, even if you initially claimed that it was VPM-B that uses "a proper measure of decompression stress" (which easily can be interpreted as an implication that other models don't).

In any case, since you haven't bothered to answer my very simple question I'm still wondering how you measure decompression stress, particularly since ultrasound-detected microbubbles in the bloodstream are irrelevant. Care to educate me?

Also, in post #1078 you say


And in post # 1089 I asked for a cite for that. Still waiting. It doesn't have to elaborate, the post # where Drs. Mitchel land Doolette "blame it all on VPM-B and bundle all those problems on me" is just fine.

We all make these posts quickly and in a few sentences or paragraphs. They touch on the salient points briefly. To deliver the full message, one could write chapters and books on decompression, or a whole career, and never get around to a full description.

Your little annoying habit of nit picking bits and pieces out of context, is neither smart or needed. Please stop it. No one needs this kind of smugness.

.

 

[Storker]

Your little annoying habit of nit picking bits and pieces out of context, is neither smart or needed. Please stop it.

No, I'm genuinely curious. How does one properly measure decompression stress?

EDIT: And when I claim that someone has said something, I'd better be able to back that up with more than just my own claim. Seems fair, does it not?

 

[ajduplessis]

You obviously didn't understand the charts. It wouldn't matter at all if I'd picked GF80/40, 40/80, 100/100, 30/85, 90/75. The charts would still show that GF lowers allowed supersaturation as slower tissues come into play -- it's a function of Buhlmann's M-values. In contrast, VPM ... well, read the post here.

Anyone here prepared to do a 170ft dive with 30min BT on GF 100/100?

 

[Storker]

• Bubble models generally emphasize deeper stops at the cost of shallow stops, so for the same decompression stop time, a bubble model will distribute the deco time at greater depths compared to a dissolved gas model

WRONG. VPM-B does not suffer from this.

I must have misunderstood completely, then. Because if I look at a 50m/30min BT dive, I get quite different stop distribution with VPM-B+2 and ZHL-B GF 40/75 (yes, I played with the GFs to get comparable total run times).


ZHL-B GF 40/75:
50m 30min
21m 2min
18m 3min
15m 5min
12m 7min
9m 11min
6m 20min
3m 41min
Total 119min

VPM-B +2:
50m 30min
27m 2min (2min longer)
24m 2min (2min longer)
21m 3min (1min longer)
18m 5min (2min longer)
15m 5min (same)
12m 8min (1min longer)
9m 12min (1min longer)
6m 18min (2min shorter)
3m 32min (9min shorter)
Total 117min (2min shorter)

To me, this definitely looks as if the bubble model distributes the deco time at greater depths compared to the dissolved gas model...

 

[Diver0001]

... snip....

@Storker

What do you get for total run time if you run VPM+0 against un-tweeked Bulhmann?

R..