Deep Stops Increases DCS

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Using CCR diagrams and depths - typical of your diving: [240ft 20min 10/50 1.2]

Its easy to see the similarity between VPM-B+3 and GF 40/70

Just saw this post so I thought I'd show some dissimilarities that I see between VPM-B+3 and GF 60/75 for your chosen profile of 240ft 20min.

1. The heatmap below clearly displays the same supersaturation pattern that the NEDU study displayed. VPM's deeper stops come at the price of continued on gassing during those deeper stops. The result is higher supersaturations than the GF profile once the diver surfaces. That pattern was also displayed by the losing A2 profile in the NEDU study. In contrast, GF gets shallower quicker (as did the superior A1 profile in NEDU's study) and surfaces cleaner as clearly shown in the supersaturation heatmap.

hmVPMGF.jpg



2. The profile created by VPM-B+3 for this dive has 30% more supersaturation exposure once the diver surfaces and about 20% overall. The only credible explanation for why the shallow stop profile in the NEDU study was superior was that it produced lower total supersaturation exposure (sometimes measured by "integral supersaturation"). ISS measures both supersaturation pressures the diver is exposed to and the time period the diver is exposed to them.

A diver should ask what benefit is VPM-B+3 providing at the cost of 30% more decompression stress at the surface?
issVPMGF.jpg


...................................
Why did I use GF60/75? I took the total runtime of the VPM-B+3 profile (89 minutes) and matched it to a GF profile. The GF40/70 does not match the runtime. So I found that both GF40/80 and GF80/70 matched pretty closely. I took their average for comparison. The key is that when assessing similarities in deco methods, keep the runtime constant.

But you don't have to use GF60/75 for GF to display superior integral supersaturation patterns. GF10/89 (about as "deep-stop-ish" you can make GFs) still produces 16% lower integral supersaturation at the surface and 10% lower overall. GF's algorithm of time allocation just seems to more naturally reflect the findings of the NEDU study.

Those are some dissimilarities that I see.
 
Can you describe exactly what the y axis represents please? Are they the absolute inert pressure above ambient of the leading tissue?

Without doing the numbers myself to check, those values look a bit low to me.

Edit. The narrative has been broken as apparently the post above that I was asking about, which is now gone, was too much for the MODs.

I expect those being attacked would have rather it stayed to be honest.
 
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It's pointless responding to Ross since he still is repeating the same arguments that failed in the original deep stop debate. And I'm not wanting to rehash that.

My post just tried to show that VPM and GF are not similar in the way represented and in fact, given the same runtime, in almost any configuration GF better reflects the main findings of the NEDU trials. Those trials demonstrated a dive profile where deep stops (or stop time skewed deeper) resulted in more decompression sickness.

With regard to
  1. Integral supersaturation -- see this link. There, as well as in many other places, Dr. Doolette affirms the usefulness of integral supersaturation and takes issue with Ross's misguided characterizations.
  2. The heat map -- see this presentation by Dr. Mitchell. At about the 34 to 35 minute mark he affirms the usefulness of the heat map for understanding the issues under consideration.
  3. Financial interest in this argument -- I have no interest in any dive enterprise nor have I been offered (much less accepted) any compensation from anyone related to this topic. The only party that I'm aware of with a financial interest in this "debate" is Ross who markets VPM software.
 
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Can you describe exactly what the y axis represents please? Are they the absolute inert pressure above ambient of the leading tissue?

Without doing the numbers myself to check, those values look a bit low to me.


In the proper supersaturation graphs from MultiDeco? The y axis is showing kPa of pressure, either in tissue off gas gradient, or supersaturation pressure, depending on the graph. You can also change that pressure unit in the program. 200 kPa is about 2 ATA.
 
Hi Ross

Are your charts dependent on the tissue compartment under consideration? I would expect the super-saturation to vary significantly over time for a slow compartment compared to a fast compartment, for example.

Cheers
 
Hi Ross

Are your charts dependent on the tissue compartment under consideration? I would expect the super-saturation to vary significantly over time for a slow compartment compared to a fast compartment, for example.

Cheers

The question... is the line drawn for supersaturation / tissue gradient tracking, just one cell, or multiple cells??

A. Multiple cells - which ever is the most significant. You can turn on and view single cell tracks too, like this example below, and see where each cell is rising to the top, and then falling away.

example:

kw_sample_celltrack.jpg


In this example (in dive supersaturation), cell # 3 is the first limiting cell. By the end of the dive, cell # 11 is in control. The zero pressure line is ambient water pressure. Note how tissues do not start / stop at this zero line. All cells start / decline lower at the tissue pressure level.

All this is inbuilt to MultiDeco, so anyone can use all these tools for themselves.

.
 
As a scientist, it always raises a red flag when someone rabidly attacks a particular argument as "junk science." Ross suggests that there is no credible evidence for redistributing stops to shallower depths. The reality is that there is very little data for any decompression model. Yes, divers have been using a variety of models successfully for years, including deep stops. None of these outcomes are done under controlled conditions, however. Comparing non-DCS decompression events across divers who dived at different times, places, and conditions, doesn't really tell you much. I don't think that Doolette, Mitchell, and Watts would claim that their arguments have the backing of a tremendous volume of empirical data. What they suggest instead, is that the limited data that are available at least suggest that red-distributing deep stops to shallower levels may provide some benefit.

It is also unclear exactly what it is that Doolette, Mitchell, and Watts are marketing.
 
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I may be missing the point, but aren't Ross's chart and the heat maps similar?

The big differences between VPM-B+3 and GF60/75 in the heat maps are the tissue loadings post surfacing. In Ross's chart, the supersaturation of the most heavily loaded compartment seems to be 55 KPA on surfacing. For GF 65/75, the maximum supersaturation appears to be just over 40 KPA. This seems consistent with the different colour on the heat map for the two algorithms.
 
I may be missing the point, but aren't Ross's chart and the heat maps similar?
Yes, at least in the sense that both are looking at supersaturation over time.

Heat maps are great for visually representing A LOT of data. Imagine 32 of Ross's saw tooth lines on one chart -- 16 for the VPM-B+3 profile and 16 for the GF60/75 profile (1 for each compartment). That would give you (in a hopelessly tangled mess) the same basic information as the heat map. But the heat map provides the information in a form digestible at a glance.

The reason Ross hates the heat map is because it is easily seen that the patterns that caused the deep stops profile to fail in the NEDU study (i.e. higher supersaturation at the surface due to staying deeper during the in water phase of decompression) are the same patterns seen in heat maps of VPM vs. GF in common technical dives like the one shown above.

For the dive shown in my post above, the question still remains: What benefit is VPM-B+3 providing to justify 30% more decompression stress at the surface? (see the integral supersaturation chart).
 
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