Bühlmann ZH-L16 and M-values

[dmaziuk]

We need to look at the 1984 version which was translated into English (I'll search for it later).

EDIT: if you're talking about Decompression - Decompression Sickness, it should be available on interlibrary loan (if libraries ever open) but it describes ZH-L12. With different half-times and M-values from ZH-L16.

 

[Jwoobs]

I am just trying to understand the concept of "tolerated surplus volumes", no need for a mathematical definition

I just re-read that section [pp. 34 - 36, 2 ed.], and it really seems to me like it has to mean tissue tension. (I also take issue with the way M-value gets thrown around to mean both the 'critical overpressure ratio' and the actual pressure, but I digress.)

As you point out, it mentions Buhlmann used solubility as well. That could mean he assigned a solubility to each compartment, and modeled the expansion of the excess gas once it comes out of solution.

I.e: Compartment holds 0.5 kg N2 / kg flesh at 10 bar. Ascend to 5 bar pressure, and it can only 0.3 kg. Assuming that 0.2 kg has not been carried away by the blood, it would take up a volume of x.yz L

I think you could divide by kg's and get pressures directly, based on the ideal gas law. Perhaps when Buhlmann was working on the ZH - ADT (ie a bubble model), it made more sense to express the tissue tension as a volume.

 

[dmaziuk]

Perhaps when Buhlmann was working on the ZH - ADT (ie a bubble model), it made more sense to express the tissue tension as a volume.

Perhaps but until you measure your body volume, and your lung volume, and drain yourself of all blood and measure its volume, and so on, and then program all that into your dive computer, there will still be a bit of a disconnect between "tension" and "volume".

 

[Jwoobs]

Well I'm thinking he had to use specific solubility like kg/kg, rather than total solubility, for the reasons you point out.

Besides, tissue compartments are models. They don't correspond to any actual human flesh 1:1.

And this is just to derive the coefficients, not actually to track it in a computer.

Without having read the original works of Dr Buhlmann this is just speculation on my part. But I know people can attack the same problem in different ways and arrive at similar answers, so maybe he was just thinking in terms of volume rather than pressure.