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Dr.A.A Buhlmann, a medical type, in is published book, "Decompression -
Decompression Sickness," Rev.2 provides the following table in regards
to O2 at altitude.
0 to 150meters 3500meters 7500meters
Ambient Pressure 1.0 Bar .68 Bar .38 Bar
Pressure of Inspired Oxygen .196 Bar .129 Bar .066 Bar
Pressure of Inspired Nitrogen .74 Bar .487 Bar .250 Bar
1 Bar = 1.01325 ATA
The fraction of O2 can be calculated from the data provided.
0 to 150meters 3500meters 7500meters
Fraction of Oxygen .196 .189 .173
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>> It appears -- and I do not have a copy of this book -- that this
table is a partial presentation of the composition of alveolar air, which
differs significantly from atmospheric air. Several reasons for this, is in
that Alveolar air is only partially replaced by atmospheric air each breath,
because of the mixing of fresh air with residual air in the anatomical
"dead space"; the inspired air is also humidified as it travels to the lungs
where the percentage composition of the gas is changed. Also to
balance this out, I would think that the figures for expired air need to be
shown along with nitrogen, oxygen, carbon dioxide, and water vapor
partial pressures. -Joan- << P.S. Aren't there any diving doctors to
respond?
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If you believe Dr. Buhlmann's data then the fraction of O2 in the
atmosphere also changes as well as the partial pressure (function of
the O2 fraction anyway). There are other sources not close at hand
which can provide more extensive data on atmospheric content at
altitude. But then again as someone has already mentioned I don't think
we are planning a dive on K2.
Mr. Carl Heinzl wrote Oct 1, 1995 to Eric Maiken:
>I appreciate your posting on this matter, however, no one has as yet
>posted any factual physiological information on why a diver would be
>hypoxic at altitude after a dive.
On Sept.30, I wrote:
>If you were breathing normoxic air from a tank at 33 ft @ 7,000ft you
>would be breathing a partial pressure of oxygen of about .37 ATA O2
>(.21 x 1.77), well above any hypoxia concerns. If you were breathing
>the air from the tank at the surface @ 7000 ft, you would have an O2
>partial pressure of about .16 ATA (.21 x .77) which is where you may
>begin to experience some minor signs of hypoxia.
Presto you are hypoxic at the end of the dive!
In this last case a Nitrox mix > 21% would keep you above the .16 ATA.
However as soon as you took the redulator out of your mouth you drop a
little below .16 ATAs O2 due to the reduced atmosphere and O2 fraction.
You would be hypoxia before you started the dive anyways.
However I suspect you are looking for an answer to another question
rather than atmospheric O2 partial pressure requirements to sustain
proper body function. I did find an interesting bit of information from
Dr. Buhlmann. He states "The adaptation to high altitude mainly
concerns the erythropoisesis with the development of polyglobulia, with
which the circulatory system's capacity to transport oxygen is
increased. The affinity of hemoglobin for oxygen decreases somewhat,
which causes an increase in the PO2 in tissues." Go figure!
Unfortunately Dr. Buhlmann is dead and can't comment.
Doug Chapman
--
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