VPM Overview

Gopichand Paturi gopichandpaturi at gmail.com
Fri Mar 14 11:09:10 PDT 2014


> Hi Robert(atdotde),
>


>
> You say, you confirmed (19). Could you show me how? Doesn't need to be
> typed, could be handwritten an scanned as well.
>

Yeah well, I tried to solve it in the thermodynamic equilibrium way solving
equations, but I was a bit messed up with 5 eqns and lots of variables.
 But I checked it with research paper of Yount though, It was actually done
by integration of Laplace equation over compression and decompression
phases.
To be more clear on validity, I cross checked both the references that gave
the same equation.
Also, I saw the implementation specifics, which also used the same formula.

>
> I haven't gotten around completely understanding the derivation the
> quadratic equation that leads to (40). But maybe I once again I haven't
> tried hard enough.
>
> I also have to admit all the talking around the bubble regeneration with
> tau_R sounds fishy to me: given it the half-time is 20160min which happens
> to be two weeks. This is much longer than any timescale encountered in
> recreational (and recreation tech) diving. Thus it could equally well taken
> to be infinite. In particular things like exp(-t/tau_r) where t is any
> diving relevant time, I am sure can be safely approximated by 1. Such a
> long timescale should not influence anything in diving. Making this
> simplification makes a lot of things shorter.
>

Yes, Actually I was really happy to see this pointing to me. I have
overlooked this fact.
This will greatly reduce some equations. Also we can take r_s = r_m, to be
valid throughout if we don't have this regeneration effects on the bubble.
Thankyou for letting me know this.

>
> Regarding "more intert gases": what is said around (42) sounds to me to
> speak against the theory of different bubbles for different gases.
>
> This actually seems strange to me also, but I understood it like this
(Please correct me if I am wrong).   If you see the parameters in the
equation, they are all the individual computed values of super saturated
pressures of each bubble.
So, when there are multiple inert gases probably he's using the weighted
avgs to come to a value of super saturation for the tissue compartment as a
whole which looks convincing !!.


I am currently working on my proposal for VPM, will send you that soon for
your opinion.

Thanks & Regards,
Gopichand.
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