Deep Stops Increases DCS

[UWSojourner]

Then maybe its time you took a fresh look:

Q. How close are 40/70 to VPM-B +3?

a/ nothing - diametrically opposed?
b/ almost the same?
c/ identical?

I pick B.

Well, I guess we've come full circle. It was statements like this that made me post here what appears below. It would be easy to "pick B" based on your chart because your chart is specifically designed to blur distinctions. Some of those distinctions appear below for a 240ft dive.

And the questions still stands for the profile below: What benefit is VPM-B providing at the cost of 30% more decompression stress?
....

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.

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?

...................................

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. A low GF of 40 or 50 seems more in line with the NEDU study though. 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.

 

[Ayisha]

The deep stop profile had 5% DCS risk; the shallow stop profile 1.6% DCS risk.

Just wondering, since the figures (5% vs 1.6% DCS risk) are less than 5% apart, are they considered to be statistically significant, especially with the small sample size of the study? Just recalling statistics classes where a difference of less than 5% is considered not statistically significant.

Honestly, the NEDU study and all the resulting discussion just confirmed to me what I and many others I know have been doing for at least a decade: it's prudent for recreationally deep dives to make a short, shallower "deep" stop and increase the safety stop by a minute or two or more depending on the depth and conditions of the dive. I know that for technical depths and durations of dives, the depth and time of the first of many stops become crucial.

Something else I've posted on these threads way in the past as well was that I see a short deep stop as not much different than a multi-level dive. I think most people at some time or another pause at different depths to see a different part of a shipwreck, reef, etc. Keeping in mind how long to stop at these varying depths while considering on-gassing/off-gassing, is similar to a deep stop.

My 1 cent worth anyway in all the muddy waters. YMMV.

 

[UWSojourner]

Just wondering, since the figures (5% vs 1.6% DCS risk) are less than 5% apart, are they considered to be statistically significant, especially with the small sample size of the study? Just recalling statistics classes where a difference of less than 5% is considered not statistically significant.

Yes, the difference was statistically significant. The ethics protocol (remember they were bending divers) required them to terminate the trials as soon as they had a statistically significant result.

 

[rjack321]

Just wondering, since the figures (5% vs 1.6% DCS risk) are less than 5% apart, are they considered to be statistically significant, especially with the small sample size of the study? Just recalling statistics classes where a difference of less than 5% is considered not statistically significant.

Honestly, the NEDU study and all the resulting discussion just confirmed to me what I and many others I know have been doing for at least a decade: it's prudent for recreationally deep dives to make a short, shallower "deep" stop and increase the safety stop by a minute or two or more depending on the depth and conditions of the dive. I know that for technical depths and durations of dives, the depth and time of the first of many stops become crucial.

Something else I've posted on these threads way in the past as well was that I see a short deep stop as not much different than a multi-level dive. I think most people at some time or another pause at different depths to see a different part of a shipwreck, reef, etc. Keeping in mind how long to stop at these varying depths while considering on-gassing/off-gassing, is similar to a deep stop.

My 1 cent worth anyway in all the muddy waters. YMMV.

5% is a typical level chosen for a "significant difference". But that doesn't mean the difference itself is more than 5 percent. A 1 in a 1,000 (1/10th of 1 percent difference) can be statistically significant given enough trials "Significant" just means that the results are potentially due to chance 5 or less percent of the time, its independent of the magnitude of the measure difference between the 2 trials. In this case its worth noting that they had to terminate the study before they even completed it because the Navy's proposed bubble model was (relatively) easily proven to be worse than the competing model.

 

[rossh]

Sorry Ross, your opinion does not equate to fact. You've stated as undisputable fact that the results of the study do not apply to tech diving. Deco science still has many unknowns and is highly theoretical. How can you make "undisputable" claims? You are over stepping quite a bit.

Ok, you choose the adjective that you like instead. But, the details still remain:

No deep stops in the nedu test.
No profile stress testing worth of mention,
No real connection to VPM-B.
etc..

To contest these facts, there is an endless amount of faked up profiles, invalid heat graphs, ISS charts, all masquerading as some kind of proof. All of it has hidden details, has undocumented or no-scientific methods. And its all generated by one man.

This whole nonsense hinges on a faked up profile, and a heat graph that has invalid.

 

[UWSojourner]

To contest these facts, there is an endless amount of faked up profiles, invalid heat graphs, ISS charts, all masquerading as some kind of proof. All of it has hidden details, has undocumented or no-scientific methods. And its all generated by one man.

I have to assume the "one man" is me .

Your statement fails to give credit to Dr. Doolette, et al, for their work at the NEDU. And the large contributions of Dr. Mitchell in the deep stop thread and his subsequent presentations. Many others contributed to the deep stop threads both on RBW and here. I did do the heat map. But it really just shows comparative supersaturation patterns and, in terms of information, is not much more than a more visual version of Doolette's deep stop skew chart.

So while I don't mind you giving me "credit", there were a lot of people contributing to helping us understand the applicability of the NEDU trials.

 

[ajduplessis]

I think it's safe to say that the whole point of the NEDU trials is that they are not claiming one is better.

THEY SHOWED that one was better for a very carefully designed experiment...

Showed one is better when there is no exact science behind it is even funnier.

 

[ajduplessis]

Yes, the difference was statistically significant. The ethics protocol (remember they were bending divers) required them to terminate the trials as soon as they had a statistically significant result.

Post dive stress like playing football/basketball, bench pressing in the gym and other descriptions found in the incident log - These you say was also strictly managed and controlled and part of the testing criteria and ethics protocols?

Soldier: My shoulder is not feeling well Dr, I think I hurt it during my gym session post dive.
Doctor: No, you are bend soldier, take a ride. We must update the dive register, our extreme deep stop schedule is bending our divers.

Science hard at work .......

 

[Freewillow]

"Soldier: My shoulder is not feeling well Dr, I think I hurt it during my gym session post dive.
Doctor: No, you are bend soldier, take a ride. We must update the dive register, our extreme deep stop schedule is bending our divers."

If the doctor does not know to which group the soldier belongs - double blind study - then the assesment is valid .

 

[ajduplessis]

Take the time and go and read ALL of the information....