Technical discussion on VPM

Lutz Vieweg lvml at 5t9.de
Tue Mar 4 14:58:43 PST 2014


On 03/04/2014 07:50 PM, Gopichand Paturi wrote:
> Well I am not clear about one thing ...Is it past patterns and
> experiences that drive decompression algorithms...or do we have explicit
> theory that involves perfect calcualtions to form the decompression tables?

The theories on decompression are very, very simplified models
of what is assumed to happen in the human body.

Experiments on humans and animals have been made over time to the
limited extent that research funding and ethics allowed, but while
their results can be said to somewhat support the usability of the
decompression models (within reasonable limits of duration, depth,
temperatures etc.), there is plenty of uncertainty involved.

Uncertainty starts even at the medical basics: While there
is a consensus that bubbles of inert gases in human tissues cause
all kinds of adverse effects, there is no certainty or consensus
on whether such bubbles are harmless if only small enough, or whether
harm is already done without any gas bubbles existing, just higher-than-
ambient partial pressures of gases.
Some researchers today claim that most DCS harm is not even resulting
from gas bubbles, but claim that the higher inert gas partial pressures
directly harm the endothelium, and that this is causing DCS symptoms -
but that is as of today a hypothesis not endorsed by a majority of
researchers.

Also, the physical properties of human tissues are far more complex
than modelled by the primitive formulas (used in practically all
decompression models today) that were originally invented to model
the behaviour of diluted gases (rather than fluid/solid tissues).

So VPM may well be less inaccurate than the old Bühlmann model with
regards to modelling what happenes in the human body, but it is sure
not by any means an accurate simulation that would allow a near-certain
prediction of whether DCS will occur or not.

Regards,

Lutz Vieweg


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