NEDU Study

[Dr Simon Mitchell]

There are a number of problems associated with using information from people who were bent while doing dives outside of a formal study.....

Hello John,

Many excellent points there. Which should give us pause to reflect on the invaluable and unique contribution to the science of diving represented by these human studies conducted by Dr Doolette and Gerth and their Navy diver subjects at NEDU. Precisely controlled dives, precisely controlled conditions of temperature and work, precisely controlled ascent rates, and a consistent case definition of DCS applied by doctors with appropriate diving medicine training. It is remarkable work.

This, of course, is not to imply disrespect to my colleagues at DAN who have tried very hard over the years to reduce the confounding factors on meaningful decompression research based around recreational diving activity. That is what Project Dive Exploration was about, and also Dr Pollock's work at events like Innerspace. The common thread there was the data were gathered prospectively (often by observers in the field) so that the number of dives, the nature of the dives and the outcome (clinical DCS and / or VGE) were accurately known. All other approaches start to run into the sort of problems you articulated in your post.

Simon M

 

[Kevrumbo]

. . .Getting off the bottom (that is, skipping the deep stops) can reduce tissue loading in intermediate and slow tissues. No matter what is done at depth, prolonging shallow stop time is effective at reducing VGE in individuals predisposed to develop them. Other strategies might work, but I am most impressed by those based on credible evidence. I call prolonged shallow stops really cheap insurance.

Neal Pollock Ph.D

https://www.ccrexplorers.com/community/threads/diving-tooh-carefully.18348/page-18#post-178445

Again the "cheapest" insurance is an extended shallow O2 profile stop, especially on top of bubble model schedules for those still choosing to use them, which the NEDU Deep Stops Study has shown (and others here like @UWSojourner have demonstrated) -put unnecessary inert gas supersaturation decompression stress on slow tissues upon surfacing.

Agreed @Dr Simon Mitchell , it's not the most "efficient" use of Total Stop Time (TST), but we as civilian sport tech divers usually don't have Ultrasound imaging or Doppler detection to monitor VGE/Decompression Stress and a shipboard Recompression Chamber always standing-by onsite like Military/Commercial Divers -so we rely on practical "efficacy", which means doing shallow stops for however long it takes to relieve those surfacing supersaturated slow tissue tensions, and that's what is most important here in this instance. . .Unfortunately we don't know how much to extend those O2 profile stops in a bubble model schedule (i.g. extra 5 minutes? 10min or 15min with an open circuit Air or backgas break?), especially over the course of consecutive days of deco diving. Qualitatively, if we have post-dive sub-clinical symptoms like extreme fatigue and/or the "niggles" (or worse -overt & acute DCS) then that's our only usual "uh-oh" sign indicating not enough O2 deco shallow time done. . . (The other end of that dilemma for consideration though is too much time of O2/CNS exposure).

At least with a gas content model and a Shearwater Petrel/Perdix with Buhlmann GF's, you can have some relative quantifiable reference value to deemphasize the deep stops and extend out the O2 stops as an option as well -for example start with 40/70 or 50/80 for day one of a multi-day dive trip, and keep that setting or optionally adjust GFHi to a lower value for conservancy as needed -either pre-dive or realtime during the dive if conditions change (i.g. physical exertion, hypothermic stress etc) -for subsequent dives on each consecutive dive day.

 

[Remy B.]

This is what I'm doing as well.

in my last deco dives I used 70/40 for a same dive profile where I used previously VPM-B+3 ( same dive location ), I don't know if it was a coincidence but I felt less tired/sleepy with the 70/40 plan, it could had been other factors prior to dive, who knows.

I used VPM-0 on shallower-shorter Deco dives, with good results as well.

I will keep using Multi-Deco but with the recommendations of Dr. Mitchell, with 70/40 which I think it has a balance between the two algorithms theories.

For correction, my mistake, I meant 40/70, that is what Dr. Mitchell personally use.

Thanks Ev2dive for bringing it to my attention.

 

[Basking Ridge Diver]

For correction, my mistake, I meant 40/70, that is what Dr. Mitchell recommended.
Thanks Ev2dive for bringing it to my attention.

Interesting you say that. First you get in trouble if you blindly follow GF without understanding them in context. I understand that GF can change depending on the dive and the depth.

Second point is I have noted 50/80 that a few folks use including Dr. Mitchell. That said there is no magic bullet... use information on the internet with a grain of salt it is worth the money you paid for it...

 

[UWSojourner]

Interesting you say that. First you get in trouble if you blindly follow GF without understanding them in context.

Can you provide some context to your comment about context? Because your sentence seems to apply to just about everything. I'm having trouble thinking of ANYTHING that is good to "blindly follow" or not understand "in context". But you chose GF as the focus. So the sentence reads (to me) more like an accusation -- that GF in some special way needs special care.

Maybe that's not your intent, but I'd like more context if you can provide it.

I understand that GF can change depending on the dive and the depth.

I think you're on firmer ground diving GF50/80 or GF50/70 across ALL dives (shallow or deep) than, for example, VPM-B+2. See this post and referenced links for context.

 

[Remy B.]

Interesting you say that. First you get in trouble if you blindly follow GF without understanding them in context. I understand that GF can change depending on the dive and the depth.

Second point is I have noted 50/80 that a few folks use including Dr. Mitchell. That said there is no magic bullet... use information on the internet with a grain of salt it is worth the money you paid for it...

To understand why I choose GF 40/70 over VPM+3 or GF 50/70-80, you will nee to read the other Thread, then watch the Expositions of Dr. David and Mitchell.

 

[boulderjohn]

To understand why I choose GF 40/70 over VPM+3 or GF 50/70-80, you will nee to read the other Thread, then watch the Expositions of Dr. David and Mitchell.

Just for your information, there was a video posted recently from Dr. Mitchell in which he said he is now using 50/80. I assume that is still true.

 

[Remy B.]

Yes I'm aware of it, that is the video I'm referring to if I'm not mistaken, but as the study mention that deeper stops show higher type 2 DCS due to the slow tissues still were on-gassing, but that he didn't know for sure how much shallower they shall start, even that their study showed Type 1 DSC on the shallower profiles they were way much less incidents that the Type 2 that of the deeper stops, since there is a balance in everything ( like I exposed in the other thread ) I see a balance in GF-40/70, am I right, or am I wrong, who knows, another study need to take place to see where the stops shall start, since there are no studies yet, nobody is right and nobody is wrong.

 

[leadduck]

BTW, did anyone see the new tables in the most recent US Navy Diving Manual rev 7 of December 2016?

For example, 40min bottom time at 130fsw requires deco stops 6min@30fsw and 66min@20fsw. That's like GFlow=105, GFhigh=90.
120min bottom time at 80fsw requires deco stops 10min@30fsw and 200min@20fsw, that's like GFlow=90 GFhigh=80.

AFAIK they were calculated with the exponential/linear model considering two phases (gas/dissolved) fitted to a ton of real dives data, and were experimentally tested.

 

[Remy B.]

BTW, did anyone see the new tables in the most recent US Navy Diving Manual rev 7 of December 2016?

For example, 40min bottom time at 130fsw requires deco stops 6min@30fsw and 66min@20fsw. That's like GFlow=105, GFhigh=90.
120min bottom time at 80fsw requires deco stops 10min@30fsw and 200min@20fsw, that's like GFlow=90 GFhigh=80.

AFAIK they were calculated with the exponential/linear model considering two phases (gas/dissolved) fitted to a ton of real dives data, and were experimentally tested.

I don't know from where you got that GF105/90, I guess you are maken assumptions

Here is a 40/40/21, based on 40/70 is closer to the Navy manual that what you mention of GF-105/90

Decompression model: ZHL16-B + GF

DIVE PLAN
Surface interval = 5 day 0 hr 0 min.
Elevation = 0m
Conservatism = GF 40/70

Dec to 40m (2) Air 18m/min descent.
Level 40m 37:47 (40) Air 1.04 ppO2, 40m ead
Asc to 30m (41) Air -8m/min ascent.
Asc to

18m (42) Air -8m/min ascent.
Stop at 18m 2:15 (45) Air 0.59 ppO2, 18m ead
Stop at 15m 5:00 (50) Air 0.52 ppO2, 15m ead
Stop at 12m 7:00 (57) Air 0.46 ppO2, 12m ead
Stop at 9m 12:00 (69) Air 0.40 ppO2, 9m ead
Stop at 6m 108:00 (177) Air 0.34 ppO2, 6m ead
Surface (178) Air -6m/min ascent.

OTU's this dive: 45
CNS Total: 15.7%

And the GF-90/90 doesn't match what you said the NAVY diving manual mention.

The 105/90 is not even possible

Decompression model: ZHL16-B + GF

DIVE PLAN
Surface interval = 5 day 0 hr 0 min.
Elevation = 0m
Conservatism = GF 90/90

Dec to 40m (2) Air 18m/min descent.
Level 40m 37:47 (40) Air 1.04 ppO2, 40m ead
Asc to 30m (41) Air -8m/min ascent.
Asc to 12m (43) Air -8m/min ascent.
Stop at 12m 1:30 (45) Air 0.46 ppO2, 12m ead
Stop at 9m 7:00 (52) Air 0.40 ppO2, 9m ead
Stop at 6m 57:00 (109) Air 0.34 ppO2, 6m ead
Surface (110) Air -6m/min ascent.

OTU's this dive: 44
CNS Total: 14.8%