At 09:10 AM +0100 8/22/97, John Brett wrote:
>I've been told by several people now that making a rapid descent
>massively increases the effects of narcosis. Does anyone here
>have a definitive answer as to why?
>
>Best guess:
>If one is finning like &^"=A3$ to get down, the exertion increases C02
>retention, and I can see that having an effect. Is this the case, and
>is this the only contributing factor?


John,

I don't know about "massively" since narcosis onset and sensitivity to same
seems to have so many individual variants, but I too have read that rate of
decent does indeed effect the likelihood of narcosis onset.

However, it doesn't seem to be related to CO2 retention.

Bove & Davis's textbook on diving medicine (latest 3rd edition 1997)
specifically addresses CO2 retention as *NOT* a factor for narcosis and
cite a study by Blenkarn that showed no arterial CO2 retention on subjects
breathing either compressed air or Heliox at 190 or 286 feet. There are
other studies that also fail to support the CO2 retention theory of
narcosis, but I won't bore you with the details.

Don't misunderstand. The effects of CO2 retention are real (and profound)
but they are ADDITIVE to not causitive of the inert gas narcosis effect (to
the best of our understanding)

I am aware of folks who *deliberately* use scooters to increase their rates
of decent on what they call a "buzz run". Personally I think they're nuts
(I do my darnest to *AVOID* narcosis) but they demonstrate other dangerous
diving practices so I avoid them in general... but that's another story.

The medical community STILL doesn't have THE WORD on the causes for inert
gas narcosis. The best hypothesis (and notice it's still called a
hypothesis and not a law!) is Meyer-Overton that states "all gases or
volatile substances induce narcosis if they penetrate the cell lipids in a
definite molar concentration that is characteristic of each type of animal
(or cell) and is approximately the same for all narcotics".

There are several physical constants involved (molecular weights,
absorbtion coefficients, Van der Waal constants, etc.) and the formation of
"clathrates" (the trapping of a molecule in the lattice-work of another
structure... like a nerve cell membrane. I can see where rapidly increasing
inert gas pressures would drive some of these changes, but all I've got
there is anecdotal evidence. Again, Bove cites a whole list of studies
exploring each of these factors as THE CAUSE. They all break-down one way
or the other as theories.

The bottom line when all is said and done are a handful of theories...
nobody really knows for sure why nitrogen makes divers act like idiots. But
I agree with you, I've heard enough stories about rapid decents (by any
means) increasing the risks for narcosis that there is most likely
something to it.

Robb W

=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
CDR Robert B. Wolov, MC, (FS), USNR
Department of Orthopedic Pathology
Armed Forces Institute of Pathology
Washington, DC 20306-6000

wolov@hi*.co* (preferred)
wolov@em*.af*.os*.mi*


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