VPM Technical Discussion

[Gopichand Paturi]

Hello Robert,
I understood that I'm beating around the concepts underlying buhlmann with
your questions and I'm happy for knowing that.

I am trying to understand the variable permeability concept precisely now.
Thanks to your questions which are keeping me on right track.

I will get back as soon as possible, to answer your questions given in the
previous mail.

Thanks&Regards,
Gopichand.



On Sat, Mar 8, 2014 at 7:38 PM, Robert C. Helling <helling at atdotde.de>wrote:

>
> On 08 Mar 2014, at 12:01, Gopichand Paturi <gopichandpaturi at gmail.com>
> wrote:
>
> Gopichand,
>
> >
> > I'm sure we have ambient pressure data during ascent or descent.
>
> Yes, that's basically given by the depth.
>
> How do you determine the radius r? My guess is that it is the actual
> unknown in this equation and we have some knowledge of the pressure inside
> the bubble in terms of how much gas is in the bubble. Is this true? Then,
> how exactly is the pressure in the bubble determined/the amount of gas? How
> is that related to the amount of gas in the tissue (the 'tension')?
>
> > Next,  As you asked, as far as my knowledge about VPM is concerned, we
> put a single bubble in each compartment to simulate the actual bubble
> formation.
> >
>
> OK, then at which size? I though there are is a distribution of bubbles of
> all sizes.
>
> > Next, Regarding the radius of the bubble,we will have to initialize it
> at the surface                (this one point I read from Eric Baker's
> research paper)...
>
> But how is it initialised? What determines the value?
>
> > It is actually initialized this way at the surface.
> > Every compartment has it's own pressure(we use this as pressure inside
> bubble at surface) i.e they are at equilibrium.
>
> I think you are confusing the pressure in the tissue and the pressure in
> the bubble. Or are they the same somehow?
>
> >
> > Next we use the formula P inside = Pambient + (2*gamma)/r.....where we
> solve this equation for every compartment to find the initial radius(R)
>
> Really? At the surface without prior gas loading the pressure in the
> tissue is the ambient pressure. That would lead to an infinite radius.
>
> > No-bubble Growth Equation:
> >
> > So this is all about "Controlling the supersaturated state"
> >
> > So here compartmental pressure (called Tissue tension) is critical.
> > Let this value be called PTC.
> >
> >          So Pressure inside compartment < pressure inside the bubble
> > This helps maintain No-growth because whenever Pressure inside
> compartment goes above Pressure of bubble, diffused gases go inside the
> bubble, expanding it.
> >
> > So to avoid this we control pressure of compartment by the below
> >
> > PTC < Pressure inside bubble   (theoritically this is possible to be at
> Equilibrium)
> >
> > ->    PTC < Ambient pressure + (S/r)
> >
> > -> PTC-Pa < S/r    (This term PTC-Pa  shows the supersaturation and
> upper bound on their difference)
> >
> > This was the term I was talking about in my previous mail.
> > The above equation for No-Growth helps maintain our Compartmental
> pressures.
> >
> > Now THIS is the whole point,
> > As you implemented supersaturation using half life times and getting
> Maximum Compartmental Pressure,
> >  I will reverse map this to the M-values that are possible while
> decompression/ascent. This helps us in formulating the deco table for
> finding the acceptable ascents with an upperbound based on the pressures
> that we get from the No-bubble growth equation.
> >
>
> I don't get this. Could you be more specific? I know of course how to
> calculate the ambient pressure as a function of time as well as I know how
> to compute the 'tension' in the compartments as a function of time (this is
> the same as in Buehlmann).
>
> Best
> Robert
>
> --
>
> .oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oO
> Robert C. Helling     Elite Master Course Theoretical and Mathematical
> Physics
>                       Scientific Coordinator
>                       Ludwig Maximilians Universitaet Muenchen, Dept.
> Physik
> print "Just another   Phone: +49 89 2180-4523  Theresienstr. 39, rm. B339
>     stupid .sig\n";   http://www.atdotde.de
>
>
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