Where Is Your GF?

[rjack321]

It's just my psuedo-theory based on the little bit I know. I didn't read any science to specifically support it.

There's plenty of evidence to support that you don't get bent from just one hypothetical leading compartment. Even assuming hypothetical buhlmann compartments equate with a specific tissue (they don't).... If "only one leading compartment" was to blame, you would never have (eg) joint pain symptoms in an elbow combined with neurological symptoms in your brain or bladder etc.

 

[stuartv]

There's plenty of evidence to support that you don't get bent from just one hypothetical leading compartment. Even assuming hypothetical buhlmann compartments equate with a specific tissue (they don't).... If "only one leading compartment" was to blame, you would never have (eg) joint pain symptoms in an elbow combined with neurological symptoms in your brain or bladder etc.

Understood.

Since "compartments" are logical constructions, not physical ones, a joint with pain and something in your brain or bladder COULD still be the same compartment, though...

 

[rjack321]

Understood.

Since "compartments" are logical constructions, not physical ones, a joint with pain and something in your brain or bladder COULD still be the same compartment, though...

If you only have 2 symptoms maybe.
When you have a whole ton of symptoms across all sorts of tissues with different levels of perfusion (blood, spinal, muscle, fat, skin, bone, and ligament) it strains credibility that a lone compartment half-time and m-value describes them all.

 

[Lorenzoid]

If you only have 2 symptoms maybe.
When you have a whole ton of symptoms across all sorts of tissues with different levels of perfusion (blood, spinal, muscle, fat, skin, bone, and ligament) it strains credibility that a lone compartment half-time and m-value describes them all.

Okay, I'm trying to get my head around this whole discussion. It certainly makes sense that if two compartments are both getting close to their M-values that the tissues associated with both may cause symptoms, even if one compartment is somewhat closer to its M-value than the other. I can even fathom the possibility of a scenario in which a first tissue associated with the leading compartment does not show symptoms, while at the same time a second tissue associated with a compartment farther from its M-value line shows symptoms. In other words, the model correctly predicts what happens to the first tissue but incorrectly predicts what happens to the second tissue. But what's news to me is the idea (from your previous post) that two tissues can, in effect, interact or act in combination to cause symptoms in one or both tissues where the model correctly predicts that neither compartment by itself causes symptoms. (I say "correctly," but it's an assumption, since it can't be tested.)

 

[rjack321]

Well be careful assuming any given tissue is associated with any given buhlmann compartment...

Every organ in the body has nerves, blood vessels, connective tissues, blood (the corneas being an exception), fat, smooth or striated muscle fibers (or both) etc etc. All those different kinds of cells have different affinities and tolerances for dissolved gas. Those cell types are all mushed together into a tissue, which is a building block of an organ. Most of the time, DCS symptoms are described / categorized at the organ or whole body level. Nerve pain, joint pain, confusion, loss of consciousness, chokes, fatigue, headache, etc. There is no such thing as DCS in one particular "leading" tissue.

We just slap a big old "half-time / m-value" out there as a hypothetical construct.

 

[Lorenzoid]

Well be careful assuming any given tissue is associated with any given buhlmann compartment...

We all should.

The bubble showers that the faster compartments are releasing are going to combine with the showers from the "full" slower compartments and be more likely to produce clinical symptoms.

 

[lv2dive]

Oops! I don’t think you told me that story!! Lol

Yup quite a few years ago I concluded that the longer "helium penalty" deco was about what I needed - whether I actually had helium in the mix or not.

I think it was about 4 years ago now, but I once did a whole week of 32% cave diving with @lv2dive and felt like poo every night. On the last day I padded the O2 stop like crazy because I had to fly the next day. Felt soooooo much better that night and realized I had spent the whole week prior sub-clinically bent :/ ooof

 

[Germie]

40/80, did not vote.

 

[lv2dive]

Ken,

I think the vast majority of your post is SO spot on! Starting with the second paragraph, especially the first sentence, I completely agree with you.

I do, however, have a difference of opinion with you vis-a-vis your first paragraph. Especially (but not exclusively) for newer tech divers, I think the details on how/why people made their individual GF choices have the potential to be very illuminating.
<end minor difference of opinion >

i wholeheartedly agree with the point you (and others) have stressed: since we are all different, one of the most important things we can do is pay attention to what our bodies are telling us. Six or more years ago, due to well-timed (for me) conversation with Dr @David Doolette, I started experimenting with a higher GFLo - obviously well before the pendulum started swinging towards that direction. I’m very grateful for that conversation, and that I prioritized paying attention to how I felt over following what was then almost-universal best practice re deep stops.

To wrap up... your last paragraph is so good I feel compelled to simply repeat it:

At the end of the day we're all physiologically different and everyone that engages in decompression diving needs to have a respect for their body, pay attention to it, and adjust their ascent schedules accordingly. Don't just adopt a GF because some nitwit on the internet suggested it.​

BTW, discussions about specific GF's are silly and are up there with Try-Athletes discussing the wattages they generate.

The GF that works for you may leave me a pretzel and visa-versa. The "safe" default used to leave a friend of mine bent quite regularly and he had to run something like a 40/50 or 40/60 to avoid getting hit (when he told me his story I suggested he get tested for a PFO, guess what he had!).

A t the end of the day we're all physiologically different and everyone that engages in decompression diving needs to have a respect for their body, pay attention to it, and adjust their ascent schedules accordingly. Don't just adopt a GF because some nitwit on the internet suggested it.

 

[Michael Guerrero]

On this last point, isn't that pretty much the same thing that that article Shearwater put on their website a few months ago (about "the helium penalty") was saying? I.e. that there is no helium penalty, but that having one built into our algorithm(s) is what has been making it safe, and that what we really need is to adjust our plan for nitrogen to match what the helium "penalty" has been dictating?

@Dr Simon Mitchell and @David Doolette have discussed this in previous threads, conferences, and papers. The idea being that while we should probably treat Nitrogen and Helium similarly in terms of the rate of on-/off-gassing, at least in the aqueous tissues, the true decompression obligations are probably more along the lines we set for Helium rather than Nitrogen. In other words, the longer deco times associated with the "Helium penalty" are probably the more appropriate deco schedules.