Deep Stops Increases DCS

[pensacolaracer]

The issue with your 50-60 percent low is that in reality, you are really down around 30 percent low.... Remember, I have watched you ascend many many times.

Use your back up petrel and put the home screen to display GF99. I'll bet you a free trimix fill you don't come within 20 percent of your low gradient factor on your way up to 10 feet below your first stop.

Even with what I have mine set at and what I like to think is a 60 foot per minute ascent, im not coming anywhere near 80 percent on the way up.

 

[Dr. Lecter]

The issue with your 50-60 percent low is that in reality, you are really down around 30 percent low.... Remember, I have watched you ascend many many times.

Use your back up petrel and put the home screen to display GF99. I'll bet you a free trimix fill you don't come within 20 percent of your low gradient factor on your way up to 10 feet below your first stop.

Even with what I have mine set at and what I like to think is a 60 foot per minute ascent, im not coming anywhere near 80 percent on the way up.

Careful what you bet - after last Saturday I've got a bit of a fire under my arse on the whole ascent rate thing. But I'll definitely take a look at it next run - GF99 is always on for the Petrel. You diving Sunday? I see Saturday is all recreational depths.

 

[pensacolaracer]

Even with your fire, it's still a safe bet. You damn near need to point the scooter straight vertical to get close to and maintain your low number.

Sunday is a fishing day. Although I am looking for a buddy tomorrow if you have the ability to take a day off work.

 

[Kevrumbo]

The interesting question is what kind of horrible type II, 'helium leaving fast tissue too quickly' hits are being flirted with by getting really shallow really fast. Unlike the slow tissue aches, pains, and chronic feeling of tyness that accompanies too much deep stop time even with a "successful" decompression, I worry that really high GF lows and relatively high helium mixes are basically binary: 99.X% of the time, nothing at all goes wrong, but that 0.Y% of the time something does go wrong, it's not the mild type of hit that occurs. Which is why I'm still at 50 or 60% for my GF low, and am closely observing Pensacolaracer as my guinea pig

Then again, going huge on the shallow O2 time to make up for way too much deep time isn't doing your odds of oxtoxing any favors, so you pays your money and you takes your chances.

Yeah . . .it's a cost/benefit paradigm choice; either high CNS O2 Exposure with the additional Oxygen deco to clean up the slow muscle/fat tissues, or risking a rare late onset type II Neuro DCS by ascending too fast & bypassing a critical Deep Stop.

I think that this is the more important implication (dilemma?) to understand from the conclusion of the NEDU Experiment. . .

 

[rjack321]

Getting an eventual hit after many, many dives is NOT inescapable. Yes, I understand the analogy and I believe it is well intentioned when it is aimed at de-stigmatizing bends. Anybody on any algorithm can get a hit. But I do not look at it with approving eyes when it can be used as a blanket statement to excuse less than effective deco strategies.

I know some very experienced deco divers that have never had to take chamber rides or IWR to treat bends. I believe I read in somewhere that Steve Lewis (aka Doppler) is one of these cases. My tech instructor never took a chamber ride in spite of spending decades teaching TDI's deep air courses in the cold, dark waters of Alaska and the Pacific Northwest. He was also very regularly organizing and executing dives to Pacific Northwest wrecks like the Admiral Sampson (320fsw) and the Bunker Hill (280 fsw). I've never taken a chamber ride, and, knock on wood, I hope I never have to.

"The only way to guarantee that you will not get a DCS hit is to avoid diving altogether". While I accept this to be true in and of itself, I refuse to use it as an excuse.

There are also better than average and worse than average offgassers out there. I have no problem with the better than average ones being tech instructors. What I do have an issue with is that their one body somehow defines success and failure.

The 1:2 RD setpoint (which had the bare bones of shallow time) used to be 220ft!!! Only after AG himself got older and started feeling like sheet did he (initially through NAUI and now through UTD) change the 1:2 setpoint to 200ft. That's not science. That's not looking at the statistical probability of getting a hit and deciding what is/isn't acceptable and basing the schedules on that. That is a single datapoint dictating an entire agencies approach.

That's what the NEDU study did do. It (for the first time) repudiated the nice sounding but false idea that deep time kept bubbles small and allowed for more efficient offgassing and hence less time shallow. That is false, the hit rate increases if you linger on backgas at depths where fast tissues are offgassing but slow continue to ongas.

If you are on a "fast inert gas" you might need to accept the shallow time penalty by lingering deep to avoid different kinds of hits. NEDU did not examine this. But the reality is that most hits are nitrogen bends anyway - even on trimix. There were some rabbit studies in the 80s which actually looked at the composition of a blood bubble even during explosive decompression - its all nitrogen and the He fraction is trivial, much much lower than the fraction of inspired helium. So lingering deep just because you are on trimix is not born out by science either. And its certainly not validated by the pearl divers anecdotes - they probably got away with super aggressive (air) deco because the DCS susceptible ones died or were so maimed they didn't contribute to the dataset.

 

[flots am]

Good so don't "pontificate" on something y'all absolutely know nothing about.

You aren't doing these dives consecutively like the Truk Dive Guides over a month's time (and myself on Ratio Deco with non-standard Deep Air since 2007) --so wtf do you all know?

I know that if I did a dive that bent me, I'd stop diving that way.

flots.

 

[Kevrumbo]

There are also better than average and worse than average offgassers out there. I have no problem with the better than average ones being tech instructors. What I do have an issue with is that their one body somehow defines success and failure.

The 1:2 RD setpoint (which had the bare bones of shallow time) used to be 220ft!!! Only after AG himself got older and started feeling like sheet did he (initially through NAUI and now through UTD) change the 1:2 setpoint to 200ft. That's not science. That's not looking at the statistical probability of getting a hit and deciding what is/isn't acceptable and basing the schedules on that. That is a single datapoint dictating an entire agencies approach.

That's what the NEDU study did do. It (for the first time) repudiated the nice sounding but false idea that deep time kept bubbles small and allowed for more efficient offgassing and hence less time shallow. That is false, the hit rate increases if you linger on backgas at depths where fast tissues are offgassing but slow continue to ongas.

If you are on a "fast inert gas" you might need to accept the shallow time penalty by lingering deep to avoid different kinds of hits. NEDU did not examine this. But the reality is that most hits are nitrogen bends anyway - even on trimix. There were some rabbit studies in the 80s which actually looked at the composition of a blood bubble even during explosive decompression - its all nitrogen and the He fraction is trivial, much much lower than the fraction of inspired helium. So lingering deep just because you are on trimix is not born out by science either. And its certainly not validated by the pearl divers anecdotes - they probably got away with super aggressive (air) deco because the DCS susceptible ones died or were so maimed they didn't contribute to the dataset.

Trivial but I would disagree with that conclusion Rich --Since Helium is such a fast molecule, of course it's going to diffuse out even before you analyze those bubbles in tissue, post-necropsy on that poor rabbit carcass. With Nitrogen's greater tissue & blood solubility, IMO you're going to see more evidence of it in pathological bubbles of tissue & blood anyway --even if the poor animal was subjected to a real-time vivisection/post-Explosive Decompression trial. . .

 

[rjack321]

Trivial but I would disagree with that conclusion Rich --Since Helium is such a fast molecule, of course it's going to diffuse out even before you analyze those bubbles in tissue, post-necropsy on that poor rabbit carcass. With Nitrogen's greater tissue & blood solubility, IMO you're going to see more evidence of it in pathological bubbles of tissue & blood anyway --even if the poor animal was subjected to a real-time vivisection/post-Explosive Decompression trial. . .

So all data to the contrary you are going to continue to do deep stops because???
They haven't worked for you personally (although I suppose the outcomes could have been worse)
The NEDU study and other people's personal experiences with VPM (which produces 'deep' stops even shallower than RD) both say shallower is better.
Nobody except Ross Hemingway, Weinke, AG, and you are promoting deep stops for as long and deep as you are doing them. Although Ross and Weinke would say you are too early too deep too. You are the only one without a financial interest in the practice. So why to argue on SB? Seems like a silly reason to risk your future health and/or bone necrosis and similar impacts down the road.

Its not like you are short of money, why not put 30/70 into a petrel and follow its profile? If you want you can "finish" the deco at 20ft and add time at 10ft to your hearts content. And you can even see your ending GF in real time on the petrel. Hang out at 10ft until its down to GF50 if you want, then compare that to hanging out until your leading compartment has dropped to GF 45.

PS the rabbit study used blood draws and then analyzed those vacuum vials of blood for gas IIRC. The fHe was lower than the inspired fHe as you might expect from the lower solubility. The bottom line is that paranoia about getting a "helium hit" due to a faster ascent up to the intermediate depths is misplaced worry. Worry away if you want to but that is not scientifically justified.

---------- Post added December 18th, 2014 at 09:06 PM ----------

and the two of you (with help from some others) have turned it into trench warfare about ratio deco.
.

Only because RD has really extreme deep stops, deeper and longer than any other approach. So if anyone needs to address the results of the NEDU study in their day to day practices its people following RD tenents.

 

[Kevrumbo]

So all data to the contrary you are going to continue to do deep stops because???
They haven't worked for you personally (although I suppose the outcomes could have been worse)
The NEDU study and other people's personal experiences with VPM (which produces 'deep' stops even shallower than RD) both say shallower is better.
Nobody except Ross Hemingway, Weinke, AG, and you are promoting deep stops for as long and deep as you are doing them. Although Ross and Weinke would say you are too early too deep too. You are the only one without a financial interest in the practice. So why to argue on SB? Seems like a silly reason to risk your future health and/or bone necrosis and similar impacts down the road.

Its not like you are short of money, why not put 30/70 into a petrel and follow its profile? If you want you can "finish" the deco at 20ft and add time at 10ft to your hearts content. And you can even see your ending GF in real time on the petrel. Hang out at 10ft until its down to GF50 if you want, then compare that to hanging out until your leading compartment has dropped to GF 45.

PS the rabbit study used blood draws and then analyzed those vacuum vials of blood for gas IIRC. The fHe was lower than the inspired fHe as you might expect from the lower solubility. The bottom line is that paranoia about getting a "helium hit" due to a faster ascent up to the intermediate depths is misplaced worry. Worry away if you want to but that is not scientifically justified.

---------- Post added December 18th, 2014 at 09:06 PM ----------



Only because RD has really extreme deep stops, deeper and longer than any other approach. So if anyone needs to address the results of the NEDU study in their day to day practices its people following RD tenents.

In modern Dual Phase Deco Theory (Wienke) --bubble trouble on Trimix starts with fast Helium diffusing into free phase bubble seeds/micro-nuclei on ascent from operational depth; it grows bigger in volume on further ascent, the bubble surface tension deceases which means the interior bubble pressure decreases (Boyle's Law expansion) and voila! --You've now got a pressure & inert concentration gradient for all that supersaturated dissolved phase Nitrogen just starting to off-gas from your Fast (i.e. Neuro) Tissue Compartments, all diffusing into that permeable & now growing larger Bubble.

All it takes for that now critical size Bubble is to start impinging on a musculo-skeletal pain receptor -or worse on a nerve root capillary/venule in your Spinal Cord. You don't need an obviously irrelevant "80's era explosive decompression rabbit experiment" to explain the further subtle but potentially deadly pathogenesis that's now evolving in vivo. . .
_______________

. . .If you are on a "fast inert gas" you might need to accept the shallow time penalty by lingering deep to avoid different kinds of hits. NEDU did not examine this. But the reality is that most hits are nitrogen bends anyway - even on trimix. There were some rabbit studies in the 80s which actually looked at the composition of a blood bubble even during explosive decompression - its all nitrogen and the He fraction is trivial, much much lower than the fraction of inspired helium. So lingering deep just because you are on trimix is not born out by science either. And its certainly not validated by the pearl divers anecdotes - they probably got away with super aggressive (air) deco because the DCS susceptible ones died or were so maimed they didn't contribute to the dataset.

No Richard . . .again your conclusion is mistaken, misleading and incorrect based on first principles (inert gas Diffusivity & Solubility -see below) and Dual Phase Theory (see above):

Breathing A Mixture of Inert Gases: Disproportionate Diffusion Into Decompression Bubbles.

Undersea Hyperbaric Med 1996;Mar(1):11-7.

Abstract

To study the consequences of diving with gas mixtures, we simulated growth of decompression bubbles using an equation system that accounts for major determinants of bubble behavior. When breathing a mixture, bubbles are smaller than expected from linear interpolation between bubbles with either of the unmixed component gases because of disproportionate diffusion effects: a) When few bubbles form, the inert gas that permeates fastest becomes over-represented, relative to the breathing gas, inside bubbles during growth; this slows further entrance of the fast gas and enhances entrance of the slower gas. b) With N2-He mixtures and few bubbles, the over-represented gas is He in aqueous tissue, but is N2 in lipid tissue. c) When many bubbles form, the over-represented gas is the one with higher tissue solubility. Our simulations indicate that the smallest bubbles always occur with breathing of one of the component gases, but which gas that is depends on whether the tissue is lipid or aqueous and whether few or many bubbles form.


VanLiew HD, Burkard ME
Dept of Physiology, Univ at Buffalo, SUNY, 14214, USA.

 

[Omisson]

There is a school of thought that the speed of the diffusion out vs on loading of additional compartments with deeper stops may be the more important elements of bubble theory as it relates to DCS - hence a get shallower sooner to decompress - but everyone I know on the science side still says the direct causation element has yet to be defined. So theories continue.