Making freediving diving tabels to prevent dcs

[DeepThought]

I think that making freediving tables should be an easier process than how they made the old scuba tables, since they were done mostly by trial and error.
In freediving you can actually make it accurate per person.

Take a freediver. Measure his residual volume, one that he can constantly achieve before diving (on a floating chair if necessary).
The guy will inhale through a spirometer (or one of those cylinders with gages inside if a spirometer create resistance, though it's not really important that the diver will get 100% full lungs).
Then we know that the diver dove down to X depth with 80% N2 and 20% O2 (or actual percentage in air since that is a proximate used for comfortable calculations).
On the ascend the diver will need to inhale from the mask or use a nose-clip with no/fluid/pipe goggles so no air will be lost.
Exhaling would be done till residual volume (the dives should be easy, coz this might cause a BO) to a series of gadgets, which I'm not sure which is available, but the object will be to measure the percentages of N2, O2 and CO2 and volume. Or, to exhale to a bag and send it for later gas analysis.
With that it is possible calculate the amount of N2 absorbed in the the body.

Now there's the tricky part - there will be a need to find a numeric comparison between N2 blood/tissue saturation and DCS, which I hope scuba science have.

Doing that for repetitive dives, different depths speeds people & tempratures, we could get an average value that will work for most freedivers out there.

Since these measurements are much harder to do on scuba, maybe even scuba science will gain valueable knowledge from that (and sponsor the experiments ).

There are a few wild variables, such as temprature and humidity difference between inhaled and exhaled air and therefore volume, but it should be calculable to a safe margin or measurable with enough instruments.

I also guess that pulmonary erection changes N2 absorption rate.
Might have to do different tables for different body types and diving profiles. It's not an easy job, but it all sounds possible to me.

What do you think?
Any reasononing flaws?
Would it be possible to push this idea to reality?

 

[Rik]

The idea sounds interesting, however I think that it isn't that easy that you would expect.

Aside from the question if the needed equipment is so easy available (in both technical and financial sense), there are also a couple of things that you haven't taken in the equation.

One of the most important contributing factors in freediving DCS is repetitive diving over hours and sometimes days. You need to be able to predict off gassing which is quite difficult to predict in an individual since this is influenced by several factors, as for example CO2 retention, temperature and hydration and not to forget: surface interval en ascent rate. I any case, I guess that it will be logistically difficult to provide anyone with his personal DCS table.

Anyway, when we are speaking about DCS tables, there have been some adaptations of existing models (Lanphier 1965), but these tables are based on SCUBA tables and the assumption that there is mathematical connection.

Sounds assuring? Well, please remember that there is no current table that is completely based on what is really happening physical. Tables are often based on the research of the U.S Navy in the last century on subjects and combined with theoretical models (Haldane, Neo-Haldane, Buhlmann and recently RGBM). It’s all theories and the reality is that is emerging doesn’t make it easier.

Personally I expect that CO2-build up and the mechanical effects at the lung at depth could quite interfere with the mechanics as expected in the current tables and models, and thus make them unreliable, especially for the deeper dives.

There has been some research done recently in Vancouver with non-invasive methods where it was possible to detect breath-hold divers off gassing, but this kind of research is still in its earliest of stages. It is however in my opinion one of the best chances to predict where the real ‘limit’ is of freediving related to DCS.

Just my 0.2 cents,

Rik

 

[DeepThought]

I said it would be EASIER, not easy.

Yup, kinda forgot off-gassing, since I consider that identicle to Scuba, except off-gassing between dives.

But, my assumption is that you can always tell how much N2 was absorbed in each dive.

With that MAYBE you can calc. off-gassing between dives by checking how much absoption there will be in the next (same profile) dives, if the assumption that diffusion rate depends on PP ratio in blood and lungs (though not tissue?).

Anyway, it's not like they have those numbers in scuba, a freediver and a scuba diver which absorbed 50ml of N2 should have the same off-gassing. Either that, or that the freediver will off-gas faster because he has some residual pulmonary erection that increases surface area between the blood and air.

I understood that CO2 retention changes for narcosis factors, but does it also changes the amount of N2 absorbed (by blood PH?)? anyway, you will know how much N2 was absorbed, and that sould be enough, since getting rid of CO2 at the surface should'nt take more than a few breaths.

Ofcoruse you will have to do massive repetition for different profiles and depths and divers.
But hopfully, you could create a table that'll tell you that a diver with Lung to Body Mass ratio absorbs about 20ml N2 in so and so dives.
Off-gassing will be the same for scuba.

Than add a safety margin, and it should be as reliable as scuba me thinks.

The only change is that since the ascent is fast, diving to any depth with high rates of N2 in tissues might be more dangerous (though CO2 retaining N2 in dissolved form till hitting the surface might negate that, if CO2 really changes N2 diffusion).

10x for your reply.
Can you elaborate more on that experiment?
And tell me more about the part of CO2in N2 diffusion?

 

[JasonWelbourne]

Tables aside, and all the complex gadgets, I would be interested to know just the basic theory that details formulaticly (is that a word?) the manner in which nitrogen is accumulated during free-diving per a single dive session, the effects of surface breathing on accumulated nitrogen, the affects of ascent speed on nitrogen accumulation, etc. So that I could work all of this out in my head per dive using min/max figures and have a reasonably good idea what was safe beyond a shadow of a doubt and what was dangerous ground...

If I have the formulas, then I can write a diving simulation program for the free diving community to evaluate N2 accumulation using diving profiles generated by a dive watch.

 

[immerlustig]

algorithms you use which come from scuba diving will never be suitable for freediving since they all calculate n2 absorbtion/offgassing with slow ascent rates . any freedive is an emergency ascent by scuba standards. offgassing after a freedive, in my opinion, is a lot lenghtier than after a scuba dive of similar duration (unless maybe your freedive ascent is also 10m/min).

to come up with a reasonable table i'd rather see a survey of as many freedivers as possible, where people describe their diving procedures (depth/time/surface breaks/over days and weeks etc). i also assume that there are more dcs cases in freediving than are actually known. with the growing number of freedivers that also dive deeper more regularly that surely can't be avoided.

the first symptom of dcs is denial!

there is a thread somewhere 'surface intervalls' with a few interesting points on intervalls.

last but not least, i don't believe anything will ever be 'beyond a shadow of a doubt'. unfortunately.

regards

roland

 

[immerlustig]

that's the thread:

http://forums.deeperblue.net/showthread.php?threadid=38376&referrerid=898

roland

 

[JasonWelbourne]

Algorithms can be defined that use ascent rate as a variable. Anything can be made a variable. And in anycase, I have already spoken of using a dive watch to input the dive profile. I think it has some real possiblities.

 

[JasonWelbourne]

This is what I have so far for the equation..

dTr ¨X [Nitrogen in the lungs @ t=0] - Tr ([Nitrogen in the Body @ t=0] + Tr) * atm(t) ¨[
___ = K * ¨U __________________________________ - ____________________________________________ ¨U
dt ¨^ [Nitrogen in the lungs @ t=0] [Nitrogen in the Body @ t=0] ¨a

where

[Depth in meters](t) + 10m
atm(t) = __________________________ * [1 atm]
10m



Not sure how well it will display, but if you paste it into notepad it should show up fine.

 

[JasonWelbourne]

Well that just didn't work too well.

Saved to a text document as Unicode.

 

[JasonWelbourne]

It is a first order differential equation, and it is very solvable. What I am missing is some of the constants. How much nitrogen does the body hold @ 1atm? What is the limiting constant for the transfer of nitrogen? Is it different when nitrogen is being transfered in a different direction? Is there anything missing from the equation?

 

[JasonWelbourne]

I just realized that even the attachment didn't work worth a flip either.

dTr/dt = K*( [(Qb0-Tr)/Qb0] - P*[(Ql0-Tr)/Ql0])

- Tr is the amount of Inert Gas that has been transferred
- K is a constant OR a function of time that expresses the limiting multiplier for the rate of transfer
- Qb0 is the initial quantity of inert gas in a tissue
- Ql0 is the initial quantity of inert gas in the lungs
- P is the pressure multiplier based on depth/time
- It is a function of time, such as
P = at+b

 

[JasonWelbourne]

One of these days I will get this right.

dTr/dt = K*( [(Qb0+Tr)/Qb0] - P*[(Ql0-Tr)/Ql0])

 

[JasonWelbourne]

This is the freediving equivalent of the equation given here:

http://www.rebreather.ca/Introductory Deco Lessons.pdf

which is

dP/dt = k(Pi - P)

 

[JasonWelbourne]

dPb/dt = Kb(Pl - Pb)
dPl/dPb = Kl(Pb - Pl)
dPl/dD = dD/dt
dPl/dt = dD/dt * Kl(Pb - Pl) * Kb(pl - Pb)
or something. I have to go look up partial derivatives to remember what I have forgotten