My Journey into UTD Ratio Deco

[PfcAJ]

You’re entitled to your opinion AJ. It’s more of a slowing of the ascent. Thirty second pause and 30 second roll up.

Yeah. A stop.

Diving a gf low of less than 5 (five. Not 50. Five) is preposterous.

 

[Kevrumbo]

@leadduck , I think your graph along with @UWSojourner 's heatmaps best illustrated the effects on the surfacing supersaturation and deco stress on the Slow Tissues caused by deeper/longer Deepstops:

Comparing GF 70/70 and 20/80 which roughly track in terms of sum deco stop time for the given bottom times:

The 20/80 and 70/70 GF's may have similar total deco stop times and profile shapes above, but @UWSojourner 's heat maps tell the true damning story showing the pattern of latent slow tissue on-gassing, supersaturation and surfacing decompression stress.

Compare below the heatmap of GF 10/82 versus GF 66/66:

Granted the heatmaps use a much deeper bottom time profile with Trimix diluent on CCR, but the same pattern of inert gas tissue tensions are inherent to Deepstops' Ascent Strategies as implied by the NEDU Study: The deeper stops of the GF10/82 profile do protect the Fast Tissues from critical peak supersaturation early in the ascent, but at the expense of greater deco stress on the Slow Tissues upon surfacing.

The practical takeaway from this is that using a Deepstop Strategy like RD 2.0 to protect Fast Tssues, you're gonna have to significantly extend your O2 deco profile beyond what RD 2.0 prescribes in order to reduce surfacing deco stress on the Slow Tissues (especially @mikeny9 , if you plan on doing consecutive days of mandatory decompression diving utilizing RD 2.0).

So in terms of Gradient Factors, given an example like @leadduck of RD 2.0 emulating a GF 5/95 profile for instance, you would have to compensate by arbitrarily reducing GFhi to something like 70 or 60 for greater conservatism.

Perhaps a look at the actual supersaturation pressure patterns might help, and stop some of the "blame it all on deep stops" nonsense arguments from developing.

View attachment 462951

Here we see that the RD profile is a bit of a mess for supersaturation: The initial ascent is 20% improved over the 30/85. The supersaturation comes to a stop in the mid ascent phase, so RDS really does protect the middle ascent from injury. The last stops and surfacing pressures are about the same for both.

Note also (not shown) is that both profiles finished and surfaced with less than the ZHL-C max value (for this dive) of 0.65 ATA.

So let me make some point relevant to the last few posts.

The "slow tissue on gas problem", did not actually cause a problem, and is insignificant to the result (just like all deep stops in real use).

The surfacing off gas is near identical in both, and a 5 minute change to bottom time would be far more significant than the small differences seen above.

Enjoy.

Sorry Ross, but VPM-B at +4 conservatism by @UWSojourner 's heatmaps above shows the Slow Tissues with the highest worst case deco stress compared to the other three GF profiles. . .

 

[leadduck]

This is why more time is spent in the shallows with UTD 2.0 than a standard Buhlmann-based profile.

No, in Kevrumbo's plots UTD 2.0 spent more time below 60ft, and less time shallower than 60ft, compared to GF30/80.

Also, it's important to understand what type of decompression stress we might be exposing ourselves to. I'd rather be more exposed to Type I DCS than Type II.

That's not how DCS works. Shifting stop time from shallow to deep (for example by using GF5/95 instead of GF30/80) does not protect fast neurological tissues; to the contrary such an ascent may result in more VGE at surfacing and a high risk of DCS type II by VGE moving into your brain through shunts or PFO.

 

[mikeny9]

That's not how DCS works. Shifting stop time from shallow to deep (for example by using GF5/95 instead of GF30/80) does not protect fast neurological tissues; to the contrary such an ascent may result in more VGE at surfacing and a high risk of DCS type II by VGE moving into your brain through shunts or PFO.

I don't think anyone would profess to know how DCS works exactly . However, this is where you and I diverge in opinions. I think getting shallower quicker puts more stress on your fast tissues, and I believe Type II DCS is more related to problems with your fast tissues, and Type I relating more to problems with your slow ones.

 

[leadduck]

I think getting shallower quicker puts more stress on your fast tissues, and I believe Type II DCS is more related to problems with your fast tissues, and Type I relating more to problems with your slow ones.

Yes, type II neurological DCS is related to fast neurological tissues but the mechanism of DCS is not as simple as the decompression model. Although we'll never know exactly, there's plenty of medical evidence that venous bubbles moving through shunts or PFO into brain capillaries after surfacing is a main culprit for type II DCS whereas the same fast tissues are well perfused and quite tolerant against supersaturation during the ascent. So in order to reduce type II DCS risk I wouldn't focus so narrowly on GFlow but foremost stay away from ascent strategies that resulted in high VGE grades in experiments.

 

[rjack321]

Thank you @PfcAJ , @Kevrumbo and @leadduck

From personal experience (see post #130). The RD approach of "protecting" the fast tissues by doing additional time ~1+ata below even GFlow30 (that time is really somewhere around GFlow -10 and GFlow 5 depending on the profile) is totally counterproductive.

I figured that out with my own body over a decade ago. I had to add O2 to deco that in RD theory didn't need it and add 5 mins shallow (also on O2), which is proportionally a significant increase in shallow time. NEDU demonstrated that extra mid-deco-ascent was counter productive with such statistical power that they had to halt the study before all the dives were even done. Spisi illustrated some of the metabolic impacts of that extra time. There is no medical evidence to support shaping the profiles that way, its an old wives tale being perpetuated by UTD as "science".

You can still use UTDs ratios. 1:1 and 1:2 are not bad starting points for total deco time at all. Unfortunately the distribution of that time is not supported by anything except AG spouting nonsense on Youtube. Stop doing GF 5/95 like profiles. Best science today for a 170ft 18/45 dive (15-30mins BT) would go straight to 70ft. A brief switch stop, then ~35-40% of the total time on 50% and 60-65% of total time on O2. Move up boys & girls, move up, your fears of "fast tissue DCS II" are irrational.

 

[rjack321]

What depths/BTs are you referring to? UTD RD 2.0 has "cascading ratio deco" for certain depths and times which might match more of the schedule you're looking for. You definitely can't perform a Buhlmann-based ascent on a UTD RD 2.0 profile, as UTD RD 2.0 is not Buhlmann; it incorporates it but it isn't the same. My buddies who set their computers to Buhlmann GFs usually end up clearing their computers anyway when we are on the shallower stops but we are doing UTD RD 2.0 profiles. Forgive me but I'm still not sure what you're asking.

You said "I'm not opposed to using Buhlmann GFs; I dive with people all the time that use them. We adjust our profile to allow for short deeper stops and we've never had a problem with someone not clearing their computer. The practical difference just isn't there."

I pointed out that at the 40ft stop (for instance) RD2 and any Buhlmann profile are basically 1ata apart. This probably doesn't make a damn bit of difference for the 170ft, 20min example. Its huge when you have a 3 hour obligation, you'd be below me for hours with a significantly slower (off)gassing gradient.

Yea I know cascade deco, no I would never use it. Its worse than 1:2 deco at matching current science and doesn't work at all for 4 hours at 85ft (my last Ginnie Springs dive). Likewise AG is totally wrong about constant setpoint deco. Just because the average ppO2 on OC 50% is 1.2 does not mean that you can do ppO2 of 1.2 on a CCR for the same time/stop over that range and create identical deco. His "theory" violates actual ideal gas laws (re: the independence of inert gases).

I have seen and read every publication ever cited by AG on RD (1 and 2). He has either misinterpreted the results, made up conclusions that don't exist, or spun "science" out of thin air. The 1:1 and 1:2 derivations of total time work and have a reasonable track record for 15-30min wreck type BTs. None of the rationales for the distribution of that time have any support anymore - especially the deep stop backgas time before the first switch.

 

[rossh]

@leadduck , I think your graph along with @UWSojourner 's heatmaps best illustrated the effects on the surfacing supersaturation and deco stress on the Slow Tissues caused by deeper/longer Deepstops:

Comparing GF 70/70 and 20/80 which roughly track in terms of sum deco stop time for the given bottom times:
View attachment 462946

The 20/80 and 70/70 GF's may have similar total deco stop times and profile shapes above, but @UWSojourner 's heat maps tell the true damning story showing the pattern of latent slow tissue on-gassing, supersaturation and surfacing decompression stress.

Compare below the heatmap of GF 10/82 versus GF 66/66:
View attachment 462947

Granted the heatmaps use a much deeper bottom time profile with Trimix diluent on CCR, but the same pattern of inert gas tissue tensions are inherent to Deepstops' Ascent Strategies as implied by the NEDU Study: The deeper stops of the GF10/82 profile do protect the Fast Tissues from critical peak supersaturation early in the ascent, but at the expense of greater deco stress on the Slow Tissues upon surfacing.

The practical takeaway from this is that using a Deepstop Strategy like RD 2.0 to protect Fast Tssues, you're gonna have to significantly extend your O2 deco profile beyond what RD 2.0 prescribes in order to reduce surfacing deco stress on the Slow Tissues (especially @mikeny9 , if you plan on doing consecutive days of mandatory decompression diving utilizing RD 2.0).

So in terms of Gradient Factors, given an example like @leadduck of RD 2.0 emulating a GF 5/95 profile for instance, you would have to compensate by arbitrarily reducing GFhi to something like 70 or 60 for greater conservatism.


Sorry Ross, but VPM-B at +4 conservatism by @UWSojourner 's heatmaps above shows the Slow Tissues with the highest worst case deco stress compared to the other three GF profiles. . .

Sorry Kevin, but heat maps are junk science.... Biased, no reference base line, or calibrations, or relevance to dimensions. Not tested or proven in any way... They are just eye candy marketing persuasions.... Its also a self serving and repeating picture. example: a GF88/66 would look better compared to a GF66/66. A GF 120/100 would look better than everything...... Obviously that is not what you want, but it clearly shows this heat map idea is junk. Has this heat map method of stress compare been used in science papers...NO.


There is only one proper measure of decompression gas pressure stress - supersaturation. As David said here on SB: "... there is broad agreement that .... supersaturation is the putative cause of DCS is injury as a result of bubble formation...". That is what our MultiDeco demonstrates using the same science formula, as used in most testing and papers and stress analysis.

************

In your post above, the comments jump right onto the "blame everything on deep stops" mantra, but upon checking the facts, that "slow tissue on gas" explanation, simply does not exist in any meaningful amount in the Spinsi test..

So what caused the difference in the Spinsi test? It's obviously not the deep stops or slow tissue problems that has been incorrectly assumed all along. I guess no one bothered to actually plot out the supersaturation values, because if they did, they would likely have excluded the minor differences.

Spinsi is searching to explain the different pro-inflammatory marker values. I wonder what it might be then?

.

 

[rossh]

That's not how DCS works. Shifting stop time from shallow to deep (for example by using GF5/95 instead of GF30/80) does not protect fast neurological tissues; to the contrary such an ascent may result in more VGE at surfacing and a high risk of DCS type II by VGE moving into your brain through shunts or PFO.

VGE is not DCS..... that is the peer reviewed position. Consensus guidelines for the use of ultrasound for diving research.

There was no statistical difference in VGE scores on the Spinsi test..... the people with a PFO were screwed no matter what profile they did.

More precisely, "screwed" means the PFO sufferers have a 5x higher risk of DCS injury under any dive conditions.

.

 

[nadwidny]

Sorry Kevin, but heat maps are junk science.... Biased, no reference base line, or calibrations, or relevance to dimensions. Not tested or proven in any way... They are just eye candy marketing persuasions.... Its also a self serving and repeating picture.
.

And your defence of deep stops/VPM isn't any of those things??

Too funny.