Hi Chris and George

    I used to work in an Anaesthesia research lab, and we found in one
of our studies (and then looked hard and found it in an old German paper
who's author I can't remember) that patients would hyperventilate ever
so slightly when placed on pure oxygen.  We though it was an error in
our readings, perhaps due to different gas densities between oxygen and
air, so tried to back calibrate, but to no avail.  Then we found this
old paper that described this phenomenon.  Hyperventilation from pure O2
will cause a slight hypocapnia which will cause vasoconstriction.  We
developed a circuit that could keep this drop in CO2 from occuring
despite an increase in ventilation.  I can send references if either of
you are interested.

Just my two cents.

Ben

George Irvine wrote:

> Chris, you are of course right here. I explained the way we do it to
> these people already. I just don't have time to included it in every
> post. The WKPP methods are, as usual, perfect.
>
>      > Breaks have to be at less than 20 minutes, and you do not
>      change the total time for them. I already explained
>      that. George,    The 20 minutes on high PO2 and 5 minutes
>      "air" break is old school still taught by the usual
>      suspects. You, and others in the WKPP, have realized that
>      shorter on times not only lower the chances of an oxtox but
>      also prevent the physiological changes that inhibit rapid
>      gas exchange. There is a study done in Hawaii at the Straub
>      Clinic (Youngblood, Nakano, et.al.)* that supports this
>      view. When subjects were exposed to a PO2 of 1.5, 84% showed
>      evidence of vasoconstriction. Of those that evidenced
>      vasoconstriction, the average onset time was 18.6 minutes.
>      There were some factors (inability to clear ears) that may
>      have increased this time slightly. The interesting thing is
>      that 43% of those subjects indicated vasoconstriction within
>      13 minutes and a third were under 10 minutes. This shows
>      that the onset of vasoconstriction occurs very rapidly and
>      is probably even faster when exposed to higher PO2 levels. I
>      believe that you are using a 12/6 toggle and Landon is using
>      10/5 which is more in line with what this study shows than
>      20/5. Obviously, once the vasoconstriction begins, any time
>      spent supposedly offgassing is wasted.     Feel free to
>      repost this as you see fit.C.
>      Chris Elmore
>      (803) 748-3055 mobile  * I have a copy of the report but not
>      the journal citation. I'm looking for where it was published
>      and give you that info when I get it.
>

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