Deep Stops Increases DCS

[LiteHedded]

Please tell me it'll be the UTD-"modified" JJ

certainly won't be the Gue version

 

[100days-a-year]

Thanks for all the info presented in such an entertaining manner.It is different to see someone else getting heat.

 

[Michael Guerrero]

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

The French Navy did a study (1) that showed somewhat higher bubble scores for divers doing trimix dives using a deep stop vs. a shallow stop strategy. They did 80m and 100m dives with relatively short bottom times (15min). The results for the deep stops get worse the deeper you go. It included 100% O2 for decompression (and incorporated EAN40 for the 100m dives).

This study also did comparisons for air dives, and included a Pyle stop on one of the profiles for a 60m dive. The single Pyle stop proved the least bubbly of all the profiles, and just slightly less bubbly than the shallow stop for the first few measurements after the dives. For repetitive dives, using deep stops was worse as compared to shallow stops when on air.

Their conclusion relating to trimix diving and deep stops is: "Actually, our results suggest that breathing pure oxygen at shallow stops seem (sic) more efficient than adding deep stops breathing trimix or intermediate nitrox. Problems encountered with deep mixed-gas dives may be as well related to the inadequacies of the base-compartment model to accurately describe multiple inter-gas kinetics and counter diffusion, as to the presence of deep stops."

As for the rate of exchange between N2 and He, Mitchell and Doolette wrote a paper in 2010 (2) where they talk about this: "Although the kinetics of nitrogen and helium is similar in those tissues where they have both been studied (64,66), lung washout experiments indicate that nitrogen washes out of some body tissues slower than does helium (17) (see Fig. 20)." The chart shows complete helium washout at approx. 6hrs vs. 10hrs for nitrogen.

It goes on to say that for aqueous tissues (those with a high water content), the rate of exchange between helium and nitrogen are very similar. For those tissues with a high lipid content (fat), nitrogen diffuses much more slowly than helium. If I'm reading the chart correctly, brain tissue is considered aqueous.

If anyone would like a copy of paper #2 pm me your email address and I'll send it. I only have the hard copy for paper #1.

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1: Blatteau J-E, Hugon M, Gardette B. Deeps stops during decompression from 50 to 100 msw didn’t reduce bubble formation in man. In: Bennett PB, Wienke BR, Mitchell SJ, editors. Decompression and the deep stop. Undersea and Hyperbaric Medical Society Workshop; 2008 Jun 24-25; Salt Lake City (UT). Durham (NC): Undersea and Hyperbaric Medical Society; 2009. p. 195-206. [cited 2013 Mar 3] Available from: http://underseaandh960.corecommerce.com/ WORKSHOPS-AND-OTHER-REPORTS/Decompressionand-the-Deep-Stop-Workshop-Proceedings-p13.html

2: Hyperbaric Conditions, David J. Doolette, Simon J. Mitchell, 10.1002/cphy.c091004, Source: Volume 1, Issue 1, January 2011, Published online: November 2010,

 

[dreamdive]

Effective on all fronts except the wallet

CCR Darling.....CCR!

 

[tomfcrist]

They did 80m and 100m dives with relatively short bottom times (15min). The results for the deep stops get worse the deeper you go. It included 100% O2 for decompression (and incorporated EAN40 for the 100m dives).

Why in gods name would anyone switch off helium to an EAN 40 mix? Of course they had bigger bubbles, they started on gassing nitrogen. Counter diffusion anyone? F-that.

 

[PfcAJ]

I switch off 18/45 and 15/55 to 50% nitrox all the time.

 

[Michael Guerrero]

Why in gods name would anyone switch off helium to an EAN 40 mix? Of course they had bigger bubbles, they started on gassing nitrogen. Counter diffusion anyone? F-that.

Figure 3 from this paper (1) compared type 1 and type 2 DCS using either heliox or switching to air during decompression. The rate for DCS on heliox was 34/999 (3.4%) and for the switch to air 25/715 (3.4%). However, about 60% of the cases for heliox alone were type 2, whereas about 5% of the cases for the switch to air were type 2.

Another interesting observation of this paper was that bubbles have the potential to enhance washout because they carry much more gas than what is dissolved in an equivalent volume of blood. I would assume that this enhancement would hold as long as the bubbles did not substantially occlude blood flow.

--------------

1: Recreational technical diving part 2: decompression from deep technical dives, David J Doolette and Simon J Mitchell, Diving and Hyperbaric Medicine Volume 43 No. 2 June 2013, which references the following three studies:

30 Survanshi SS, Parker EC, Gummin DD, Flynn ET, Toner CB, Temple DJ, et al. Human decompression trial with 1.3 ATA oxygen in helium. Technical Report. Bethesda (MD): Naval Medical Research Institute; 1998 Jun. Report No.: 98-09.

31 Gerth WA, Johnson TM. Development and validation of 1.3 ATA PO2-in-He decompression tables for the MK 16 MOD 1 UBA. Technical Report. Panama City (FL): Navy Experimental Diving Unit; 2002 Aug. Report No.: 02-10.

32 Tikuisis P, Nishi RY. Role of oxygen in a bubble model for predicting decompression illness. Report. North York (ON, CAN): Defence and Civil Institute of Environmental Medicine; 1994 Jan. Report No.: 94-04.

 

[dreamdive]

However, about 60% of the cases for heliox alone were type 2, whereas about 5% of the cases for the switch to air were type 2.

Ahhhh, so what were the other 35%???

 

[Kevrumbo]

The French Navy did a study (1) that showed somewhat higher bubble scores for divers doing trimix dives using a deep stop vs. a shallow stop strategy. They did 80m and 100m dives with relatively short bottom times (15min). The results for the deep stops get worse the deeper you go. It included 100% O2 for decompression (and incorporated EAN40 for the 100m dives).

This study also did comparisons for air dives, and included a Pyle stop on one of the profiles for a 60m dive. The single Pyle stop proved the least bubbly of all the profiles, and just slightly less bubbly than the shallow stop for the first few measurements after the dives. For repetitive dives, using deep stops was worse as compared to shallow stops when on air.

Their conclusion relating to trimix diving and deep stops is: "Actually, our results suggest that breathing pure oxygen at shallow stops seem (sic) more efficient than adding deep stops breathing trimix or intermediate nitrox. Problems encountered with deep mixed-gas dives may be as well related to the inadequacies of the base-compartment model to accurately describe multiple inter-gas kinetics and counter diffusion, as to the presence of deep stops."

As for the rate of exchange between N2 and He, Mitchell and Doolette wrote a paper in 2010 (2) where they talk about this: "Although the kinetics of nitrogen and helium is similar in those tissues where they have both been studied (64,66), lung washout experiments indicate that nitrogen washes out of some body tissues slower than does helium (17) (see Fig. 20)." The chart shows complete helium washout at approx. 6hrs vs. 10hrs for nitrogen.

It goes on to say that for aqueous tissues (those with a high water content), the rate of exchange between helium and nitrogen are very similar. For those tissues with a high lipid content (fat), nitrogen diffuses much more slowly than helium. If I'm reading the chart correctly, brain tissue is considered aqueous.

If anyone would like a copy of paper #2 pm me your email address and I'll send it. I only have the hard copy for paper #1.

---------------------------------------

1: Blatteau J-E, Hugon M, Gardette B. Deeps stops during decompression from 50 to 100 msw didn’t reduce bubble formation in man. In: Bennett PB, Wienke BR, Mitchell SJ, editors. Decompression and the deep stop. Undersea and Hyperbaric Medical Society Workshop; 2008 Jun 24-25; Salt Lake City (UT). Durham (NC): Undersea and Hyperbaric Medical Society; 2009. p. 195-206. [cited 2013 Mar 3] Available from: http://underseaandh960.corecommerce.com/ WORKSHOPS-AND-OTHER-REPORTS/Decompressionand-the-Deep-Stop-Workshop-Proceedings-p13.html

2: Hyperbaric Conditions, David J. Doolette, Simon J. Mitchell, 10.1002/cphy.c091004, Source: Volume 1, Issue 1, January 2011, Published online: November 2010,

Critical question: What were the statistical results of those divers with Doppler/VGE bubble formation counts also exhibiting acute DCS Signs/Symptoms?

 

[Michael Guerrero]

However, about 60% of the cases for heliox alone were type 2, whereas about 5% of the cases for the switch to air were type 2.

Ahhhh, so what were the other 35%???

The rest were type 1 for both profiles. Let me be clearer. Of the 34 cases of heliox-only DCS, approx 60% were type 2 and the rest were type 1. Of the 25 cases of nitrox use, approx. 5% were type 2, with the rest being type 1.


---------- Post added December 20th, 2014 at 04:26 PM ----------

Critical question: What were the statistical results of those divers with Doppler/VGE bubble formation counts also exhibiting acute DCS Signs/Symptoms?

Not sure I understand the question, but every study I've seen has reported markedly higher bubble scores with both deep stops and helium vs. those with shallower stops and some form of Nitrox. They have also reported higher incidence of type 2 DCS with those same deep stop/helium-only profiles.