[PATCH] User-manual: heat map

[Rick Walsh]

On 26 Oct 2016 23:46, "Willem Ferguson" <willemferguson at zoology.up.ac.za>
wrote:
>
> Thanks very much for the feedback.
> Top diagram no problem. I will manipulate the gas pressure histogram to
match a column in the heat map.
>
Thanks Willem,
I see that you have sent another patch, and looked at the text, but I have
a few very busy days coming up and will  probably be unable to test it and
see the updated image.

> Regarding the bottom diagram, I would rather want to leave that for
someone else. The reason is that I am approaching Simon Mitchell's
interpretation with caution. I am keeping a sharp eye on developments but I
am not persuaded yet. Main reasons are twofold: 1) His interpretation that
I have seen comes from one single experiment in the USA where the measuring
unit was the presence or absence of DCS: no Doppler or other physiological
measurements were made in that experiment. 2) His conclusion that gas
loading in the SLOW tissues contributes to DCS. This is counterintuitive,
for instance in our understanding of isobaric counterdiffusion where the
effects on FAST tissues is important in contributing to DCS. There is no
physiological explanation that I have heard of why the slow tissues
specifically should contribute to DCS and not the fast tissues, given our
present assumptions of the off-gassing process. Mark Powell discusses
several DAN-based experiments that purport the advantages of bubble models.
These are the main reasons I have not been convinced yet. Also, Bühlmann
and VPM-B dives need to be compared in terms of bubble characteristics
(i.e. the currency of the VPM-B algorithm) and simple comparisons of inert
gas loading may not give the whole picture. So, I am not the best person to
reconstruct the bottom diagram.
>
I'm happy to create another diagram. Especially since I've worked out how
to arrange things better in gimp (previously I'd only really used it to
crop, resize, and colour-correct photos).  But it may have to wait a bit.

I didn't mean the comparison to "prove" that the Bühlmann model is better
than bubble models, more just an effective way of illustrating that: (a)
deep stops can reduce the gradient significantly in fast tissues in the
early stages of decompression; and (b) the additional ongassing of mid-slow
tissues during the deep stops means that the gradient in them is greater
upon surfacing than if the deep stops were omitted.

Fwiw, the "deep stop profile" in the current graphic was my actual dive.
The other profile was doctered in the xml file to remove the deep stops.

>From my understanding, isobaric counterdiffusion is an issue for deep
trimix open circuit (or cc with oc bailout) dives with relatively abrupt
gas switches from high He to lower He and higher N2 mixes.  I had a little
play and could not get the heat map to show anything noticeable here.  This
doesn't mean ICD can be ignored as a concern, or that the heatmap is
invalid, just that the heatmap is probably the wrong tool to assess it.

I did actually see a paper by Simon Mintchell on a study he had done on a
physical model of the inner ear (a very fast tissue), to assess ICD. And I
think the conclusion was that ICD was a very real concern for deep oc
trimix diving.  I don't think he mentioned this in the presentation, which
was mostly about other people's research.

> AI would appreciate any comments, suggestions or insults very much.
>
I'll keep trying to give comments and suggestions.  No need for insults!

Cheers,

Rick
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