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Scott,

Wow - every time I read one of your posts I learn something new. 
Fabulous.

Comments and questions below.

Scott Hunsucker wrote:

> >  I was under the impression that a large
> > reason for the breaks (and a large reason for the fact that they
> > don't
> > have to be subtracted from the deco) is that the high PO2's cause
> > vasoconstriction, which in turns reduces efficacy of offgassing.
> 
> Fair statement, but if the efficiency of deco is reduced by something,
> would it not make sense that the time spent at deco would thereby have
> to be increased?

Well, my simplistic view of it was that the model that we're basing our
deco on (Buhlmann) is primarily statistically based.  As such, it would
already have taken into consideration the decrease in efficiency. 
Therefore, by doing something that reverses that, you are getting a deco
advantage not described by the model.

> and soft tissues within four hours.  So you see the short BG breaks
> are only long enough to just allow the blood to return to normal
> values and not really time to offset any possible negative effects of
> vasoconstriction; 

Fascinating.  OK, when I first posted my message, vasoconstriction
hadn't been brought up yet.  However while I was making my post Trey was
apparently off composing a fairly detailed message which included
vasoconstriction (see WKPP + DECO).  In there, he mentions exactly the
same thing (not surprising since I'm sure he's the one I got it from
originally) - that is to say he makes mention of the breaks reversing
vasoconstricution thus increasing efficiency.  Here's his comment:

Trey sez:

> 3) , to
> speed the deco. The speed is accomplished by three
> mechanisms; 1) the lungs do not go ahead and add
> layers of cells to protect themselves if the
> exposure is kept in short shots of high ppo2, so the
> gas passes as it should. 2) the swelling and
> asthma-like reaction of the lungs is prevented,
> halted and reversed, so the gassing is more
> efficient, and 3) the vaso constricting effect of
> the high ppo2 is offset enough to open up the
> vessels in the tissues ( and the capillary beds of
> the lungs) for more rapid offgassing.

So here's my question.  I have yet to find an instance where something
that Trey said was (verifiably) wrong.  That's not a shot, that's
sincere.  So likely I'm misunderstanding something here.  It sounds like
Trey is saying that the breaks are increasing efficiency by reversing
vasoconstriction, yet you say the breaks aren't long enough for that to
happen plus the vasoconstriction does not really impair the offgassing
at the PPO2's that we're talking about (1.6 and less).  So can either
you or Trey clear up my confusion?

> I do hope that I have answered your question, and maybe
> some others along the way.

Absolutely.  Top-notch post, as always.

-Dave
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