Deep Stops Increases DCS

[ajduplessis]

The only thing the nedu study confirmed is common sense. The longer you stay at depth, the more prone you are to decompression sickness.

Secondly there is a massive difference between spending 1-2 min holding/moving through a deep stop vs double digit figures (~25min) claiming to be the same thing!

The more we agree decompression is not an exact science, the more some individuals insist that tried and extensively dived results is bad for you (VPM-B). Decompression is a personal choice at the end of the day.

Lastly I am skeptical when one claims to better than the other, especially when the bulk of it is not an exact science........

 

[PfcAJ]

Ross, we went over this line by line weeks ago. 40/70 is nothing like +3.

Thermal stress wasn't tested as thermal stress was a controlled variable. The only variable changed was stop distribution.

Putting "FACT" after saying the nedu tested thermal stress doesn't make it a fact. Sorry man.

 

[Jack Hammer]

...Their results do NOT apply to tech diving practices. Those facts are indisputable....

.

Please share your scientifically conducted, man tested, peer reviewed study to back up these claims.

 

[rossh]

Please share your scientifically conducted, man tested, peer reviewed study to back up these claims.

I don't need to show anything beyond plain math. Its their to task show how they bridged such a wide gap from shallow to deep. But the nedu did not do that and is not interested in tech practices - they test only dive practices that they do - really shallow model designs.

They tested between 60ft and 20ft - for two hours. Deep stops are for this profile, is 70 to 100ft - for 7 minutes. Not the same thing - not even close. And faked up VPM-B +7 profiles do not count.

The whole issue here - is the problem of "Can a shallow test set be converted to represent a deep stop tech practice"? I say no, and I have demonstrated why. There is no connection to deep stop profiles. There is an assumption by some that they are the same, but its not valid.

 

[rossh]

Ross, we went over this line by line weeks ago. 40/70 is nothing like +3.

Thermal stress wasn't tested as thermal stress was a controlled variable. The only variable changed was stop distribution.

Putting "FACT" after saying the nedu tested thermal stress doesn't make it a fact. Sorry man.

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.


But please note the enormous elephant in the room. Advocates of this nedu test, claim that VPM-B is no good because its too short. But then, the recommended 40/70 is almost the same as VPM-B and still well under the Nedu test time. What a conundrum.



The test procedure was to make them cold, and induce DCS through thermal effects. They did not at any time, ascend in a manner that produced excess or high profile stress. In fact (except for the first stop) all profile stress was extremely low, or at times completely absent of any supersaturation. Those are facts. Go take a look - its just math.

.

 

[UWSojourner]

Thanks for the link to this post. I guess (please correct if wrong) that the integral runs from the beginning of the dive to its end, but does not include post-dive supersaturation on the surface, right?

This is not correct. A critical part of decompression occurs on the surface. Therefore it's part of the integral supersaturation calculation.

If the integral runs to infinity, then why is it so important that the dive time is the same; i.e. why is there such a fundamental difference between a stop at 0.001ft and one at 0ft?

If you try to compare integral supersaturation to vastly different dives, then you have to bring in a lot of other factors to use it properly. One obvious example would be a dive to 15ft for 2 days. That dive would load up the compartments and when you returned to the surface you could calculate ISS. But studies have shown that divers can return directly to the surface fully saturated from about 20fsw without developing DCS. So there seems to be a threshold value that must be exceeded for DCS risk to start developing. Dr. Doolette discussed the idea of a threshold in my link that you referenced.

But when you compare exactly the same dive, only varying by how you distribute the stop time, the integral supersaturation can be used to compare relative levels of decompression stress.

I have used thresholds (e.g. 20fsw) to look at integral supersaturation for different profiles, for example VPM-B vs GF. Reflecting a threshold only helps the shallower GF profile. The reason is that all the faster compartments exceed the threshold in both profiles, but due to the lower on gassing in the slower compartments in the shallower model it is sometimes true that more of the slow compartments never reach the threshold in the GF profile and therefore never contribute to integral supersaturation. This makes the ISS difference more pronounced (better for GF). I've declined to post charts incorporating a threshold just because the problem with VPM and benefit of GF is demonstrated without that adjustment and we'd spend another 2 years chasing more meaningless posts, charts, and conspiracy theories by Ross if I did.

 

[Jack Hammer]

I don't need to show anything beyond plain math. Its their to task show how they bridged such a wide gap from shallow to deep. But the nedu di not do that and is not interested in tech practices - they test only dive practices that they do - really shallow model designs.

They tested between 60ft and 20ft - for two hours. Deep stops are for this profile, is 70 to 100ft - for 7 minutes. Not the same thing - not even close. And faked up VPM-B +7 profiles and do not count.

The whole issue here - is the problem of "Can a shallow test set be converted to represent a deep stop tech practice"? I say no, and I have demonstrated why. There is no connection to deep stop profiles. No one has any evidence to say otherwise!

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.

 

[UWSojourner]

My view however is this. When you do decompression dives, you only have two choices:

1. You protect the fast tissues by doing deep stops. The trade off is you have higher supersaturation in the slower tissues when you surface.

2. You protect the slow tissues by doing shallow stops. The trade off is you have increased supersaturation in the fast tissues when you surface.

Hi Macan,

I don't think this is accurate. First, it IS possible to protect both fast tissues and slow tissues. All you have to do is add deco time and keep both fast and slow tissue compartments at arbitrarily low supersaturations. Second, and this may just have been a typo, but in your point #2, the shallow profile would have increased supersaturation in the fast tissues at the start of the decompression, not when you surface.

The NEDU result deals with efficient decompression. They concluded that bubble models were not more efficient and so declined to use them. Prior to the trials it was believed (certainly it was mantra by bubble model people) that a smarter profile using bubble dynamics would allow you to either 1) exit the water in less time for the same decompression risk, or 2) use the same decompression time and exit the water with lower decompression risk. The NEDU trials showed exactly the opposite. If you want to dive bubble models, the NEDU trials would imply you need more deco time to achieve the same DCS risk as a shallower stop model.

 

[PfcAJ]

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.


But please note the enormous elephant in the room. Advocates of this nedu test, claim that VPM-B is no good because its too short. But then, the recommended 40/70 is almost the same as VPM-B and still well under the Nedu test time. What a conundrum.



The test procedure was to make them cold, and induce DCS through thermal effects. They did not at any time, ascend in a manner that produced excess or high profile stress. In fact (except for the first stop) all profile stress was extremely low, or at times completely absent of any supersaturation. Those are facts. Go take a look - its just math.

.

40/70 is not like +3. On a super short BT they might look similar, sure, but on anything longer or deeper (god help you if its both long and deep) they diverge a LOT.

Again, Ross, if thermal stress was tested why did the profile with the deeper stop distribution produce more DCS?

 

[UWSojourner]

The only thing the nedu study confirmed is common sense. . Lastly I am skeptical when one claims to better than the other, especially when the bulk of it is not an exact science........

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. We can't forget that we now have hard data points of manned trials ending in DCS. The deep stop profile had 5% DCS risk; the shallow stop profile 1.6% DCS risk. That result was a surprise to the NEDU scientists, but at least they allowed science to guide them -- they declined to switch to bubble models based on the NEDU results.