GF LO

[beldridg]

That's what makes no f'ing sense. My average dive for the past couple years averages 30 minutes of deco, especially swimming. This was a lazy scooter dive, minimal exertion, and minimal deco comparatively. It's just proof that no matter what you set your gfs or how you dive, there's so many other factors that play into it that it's a crap shoot. Especially when you add the pfo into it. I looked at my logs and it's been about 2.5 years since I had any major symptoms till today..

For sure, there are many unknowns.

One thing that comes mind (beyond the PFO) is that you were not exerting yourself during deco on this specific dive as it sounds like you were doing during your previous dives.

I'm not a doctor or a decompression expert, but during swimming, you are probably off-gassing faster or more efficiently because of your increased respiratory rate (vs. being on a scooter). I would put it into the same category of risk factors like hot on the bottom, cold on deco (hence why I now always use a heated vest on deco dives in California water).

I don't know if it was a factor, but it could have been. I also don't know if there have been any studies done about the "efficiency" of decompression when working or exercising vs not.

Best of luck with your PFO closure.

- brett

 

[boulderjohn]

I don't know if it was a factor, but it could have been. I also don't know if there have been any studies done about the "efficiency" of decompression when working or exercising vs not.

This presentation by Dr. Neal Pollock includes video of divers associated with Dr. Richard Pyle doing minor gymnastic routines during deco to keep the blood flowing. He obviously believes in it.

Just as a tiny, picky point, the only reason respiratory rate is a factor is because it is associated with the increased blood flow. It is the that perfusion that is assisting the off-gassing.

 

[rddvet]

Good luck @rddvet

Ditto.

Thanks

Just get it done and quit dicking around with it.

I'm trying. Work schedule makes doing things like this tough

 

[_Ralph]

The light deco diving that I do, 30 doesn’t hamper too much... usually first stop is around 12-15m for a total deco of 30-40min or so...

If there is much lugging of gear, I prefer a GFHI of 80 vs 85, both with a nice 5-10min float when the conditions allow, slowly getting bottles and DPV’s sorted for land before getting out..

Profiles are multi level, usually down to 50-60m for 15-20min, then up to 30-40m for another 40-50min for a nice 90-110min dive

If I was straight down and back up for my dives, I would look at changing it... I haven’t gotten ‘round to it for the diving that I currently do..

_R

 

[Scuba Client]

your recommendation is the same reason that Shearwater has/had 30/70 as the default on their computers. Pollock came out saying around 80% of your GF-Hi which is what I use so either 50/70 or 60/80

Shearwater on their Perdix was 35/75

 

[Scuba Client]

While I realize this has been addressed in other forums I am wondering what you guys are doing for GF LO?

For years I have been using GF LO at 30. I was advised to do this by a hyperbaric doc who is a NOAA DMO, amongst other credentials.

These days I am reading where folks are using 50 as GF LO based partly on Simon Mitchells' discussions on this.

Professor Mitchell was unsure whether 80 or 85 was to high. He uses 40/74.

 

[Scuba Client]

Simon Mitchell gave lots of input on this article and proofread it: Evolving Thought on Deep Decompression Stops

David Doolette wrote this one: Gradient Factors in a Post-Deep Stops World

I talk things through with buddies prior to the dive so we are doing the same thing. That has recently been in the 60/75 range. David Doolette's article was influential in that decision for all of us.

Professor Mitchell wouldn't debunk his own bubble model over the gas model.

 

[boulderjohn]

Professor Mitchell wouldn't debunk his own bubble model over the gas model.

What are you saying? Are you saying that Simon Mitchell did not in fact help me write that article, as the publishing of it clearly says? Are you saying he did proofread it?

Next, what makes a bubble model "his own"? He did not invent a bubble model. The two main proponents of bubble models were David Yount (VPM) and Bruce Wienke (RGBM). Richard Pyle is the one who made deep stop theory and bubble models famous, and he is often credited with originating the idea, but in the very publication in which he introduced it, he gave credit to Yount and Wienke as the original thinkers. I have never heard of Simon Mitchell being credited with having anything to do with the creation of either of those models.

Mitchell has has said many, many times that in the early days of deep stop theory, he embraced the idea of deep stops and used them. He has since changed his mind. If you look at the transcript of the 2008 UHMS workshop on deep stops, the conference that introduced us to the 2008 NEDU study, you will see Mitchell in his role as moderator trying (and failing) to bring the group to consensus--they could not even agree on a definition of deep stops. You will also see that the first research on deep stops that was presented there, especially the NEDU study, did not support deep stops. Mitchell is a scientist, and as such, he follows the research, and that workshop was where the research was pushing his mind change.

Interestingly enough, data supporting deep stop algorithms, specifically RGBM, was presented there by Bruce Wienke, but the numbers he presented were his own, unpublished data. Dr. Neal Pollock flat out asked him where he got those numbers, and Wienke's very evasive response--or failure to respond--is telling.

Simon Mitchell has been very up front about his own diving preferences. In this presentation in 2016, he reveals his use of Buhlmann with GFs, and IIRC, he was using a GF lo of 50. He was specifically not using Yount's VPM or Wienke's RGBM.

In this very long ScubaBoard discussion, you will see Dr. Mitchell clearly express his views as he battles it out with Ross Hemingway, an ardent supporter of deep stops and VPM. IIRC, Bruce Wienke made a brief appearance in the discussion (username - BRW).

 

[wetb4igetinthewater]

In this very long ScubaBoard discussion, you will see Dr. Mitchell clearly express his views as he battles it out with Ross Hemingway, an ardent supporter of deep stops and VPM. IIRC, Bruce Wienke made a brief appearance in the discussion (username - BRW).

Thanks for posting that. Bookmarked it for later reading.

 

[flymolo]

Adding 2 or 3 minutes to a 3 min "obligation" is doubling your deco for basically no effort at all.
Adding 2 or 3 mins to 4 hours of deco is not a substantive change.

I will always stay longer than required if its meaningful and helpful.

The 80 is my GF hi on short dives. The GF lo is 50.

I think we mostly all agree that straight Buhlmann is too aggressive and increases the risk of DCI. So, let's start off with saying that a GF Hi of 100 is a bit too aggressive for almost all dives, except maybe in an emergency where the risk of certain death is greater than the risk of getting bent.

Remember, GF hi is based on padding the M values as established by the stock generic Buhlmann algorithm. The lower your GF hi, the greater the padding.

GF 50/100 - 90' for 50 minutes:
30' - 1 minute
20' - 1 minute * switch to O2
10' - 1 minute

GF 50/95 - 90' for 50 minutes:
30' - 1 minute
20' - 1 minute * switch to O2
10' - 2 minutes

GF 50/90 - 90' for 50 minutes:
30' - 1 minute
20' - 1 minute * switch to O2
10' - 3 minutes

GF 50/85 - 90' for 50 minutes:
30' - 1 minute
20' - 1 minute * switch to O2
10' - 4 minutes

GF 50/80 - 90' for 50 minutes:
30' - 1 minute
20' - 2 minutes * switch to O2
10' - 5 minutes

GF 50/75 - 90' for 50 minutes:
30' - 1 minute
20' - 2 minutes * switch to O2
10' - 6 minutes

It seems silly, but personally on a dive with this kind of profile, I feel better sitting until my SurfGF is 80 than 85. Total difference in time is 2 whole minutes, not a big deal in the grand scheme of things, but the deco is more than double a SurfGF of 100.

Now let's look at what happens when the deco obligations start getting longer and longer.

Let's say a dive profile (50 minutes @250') running straight Buhlmann calls for a total run-time of 211 minutes, with 72 minutes at 20' and 10'. Same dive profile, but with 50/85 calls for total run-time of 237 minutes with 85 minutes at 20' and 10' (a padding of nearly 30 minutes total deco and a bakers dozen extra minutes at 20' and 10'). And same profile with 50/80, 245 minutes total r/t, 90 minutes total at 20' and 10' (+34 minutes total / +18 minutes shallow).

Running straight Buhlmann on a dive like that will likely leave me a pretzel, and while running 50/80 on a dive like that will leave me fine, I've also personally found that 50/85 on a dive like that will also leave me fine.

Summary: On a really short deco, I personally prefer to be more conservative because I feel better. On a really long deco, where the padding enabled via GF gets further away from the Buhlmann M-values, I feel fine running a slightly higher slope.

These are really interesting perspectives. Thank you.