On Thursday, March 01, 2001 6:52 PM, Huw Porter wrote:

(snip)
> >Vigorous exercise can have the same effect on the divers body in terms of
> >bubble formation as does violently shaking a bottle or can of soda!  :-)

> And surely the effect of anaerobic exercise on the muscles (reduced oxygen
> saturation, increased (er, lactates?) and carbon dioxide etc (I'm
> definitely no physiologist!) must be a factor too?

> (...and don't call me shirley)

Hi, Huw.  G'Day, Mate!  What you said is apparently correct.  (I stress
'apparently' because the jury's still out when it comes to a complete
understanding of all of the causes of DCS - and I surely won't call you
Shirley!)  :-)

I've mentioned before a book called, 'Beating the Bends' - sub-titled, 'The
diver's guide to avoiding decompression sickness', by Alex Brylske.  It's
written for the lay-person and for those who don't have a copy let me quote
an extract from the section on "DCS Susceptibility Factors" - with the
understanding that typos, etc. are mine:

"HEAVY EXERCISE:  Indications are that exercise may have a very significant
impact on the development of DCS in many ways.  First, the motion of
exercise may help form gas seeds by the friction and low-pressure areas
created as tissues and joints rub against each other.  Changes in blood-flow
dynamics brought on by exercise may also help produce micro-nuclei.  This is
explained by phenomena known as Reynolds cavitation and tribonuelation.
Through flow dynamics and friction, these forces cause low-pressure areas
throughout the body, which can become the site of micro-bubble formation.

Clear evidence exists that heavy exercise before diving can cause
significant silent bubbble development.  Research with NASA's space-shuttle
astronauts has shown that bed rest before a mission is effective in reducing
silent bubbling during decompression from the shuttle's 14.7-psi environment
to the 4.3-psi internal pressure of a space suit.  A prudent conclusion from
all this experience might be to not only avoid any strenuous activity - such
as a vigorous workout - before diving, but also to rest as much as possible.

Heavy exercise during the dive increases circulation and accelerates uptake
of nitrogen.  After you stop exercising, outgassing of nitrogen occurs more
slowly.  Unfortunately, most decompression models assume that ingassing and
outgassing occur at the same rate.  Additionally, just as it does at the
surface, exercising while at depth increases the turbulence of blood and
creates low pressure centres that could increase the number of gas seeds.

Conversely, some researchers believe that a moderate amoount of exercise
might actually assist outgassing of nitrogen during decompression.  The
trouble is, no one has been able to quantify what a "moderate" level means.
In the final analysis, no current decompression model can accurately take
into account such variations as circulation.  The concensus is to avoid
heavy exercise before, during, and even after diving."

And for Giovanni, there's an excellent section called, "Turning on your
computer shouldn't mean turning off your brain"   :-)

Strike