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Some time ago, there were a series of posts querying a paragraph from
John Lippmann's book "Deeper Into Diving"... and noting an almost
identical paragraph in the NOAA diving manual Oct 1991.
The gist of this paragraph was that a diver ascending from a high
altitude dive breathing AIR would could experience symptoms of hypoxia.
The discussions on this list sort of hung-up at the point where:
1/ No-one could really come-up with a solid reason for suffering
symptoms of hypoxia after switching from air at depth to air at a
breathable (although high) altitude.
2/ The thought occurred that if switching from AIR was a problem,
then switching from NITROX, or even O2 would be worse.
At that time I promised to try to contact Mr Lippmann and
ask him if he could clear things up for us.
Well........... Sorry but I don't have a magic answer, but after
about 2 months, I did finally manage to interrupt his breakfast and talk
with him for a while.
Since I caught him "on the hop", the following may not be a
complete answer........
*In his book, he was actually describing the ASCENT from depth,
where the PO2 would be relatively high (above 0.21), to altitude, (say
0.16). The problem he saw is in a a sudden switch. Pulse rate,
circulation, metabolism are set-up to run happily while at normoxic
conditions, but require adjustment to cope with a NEAR-HYPOXIC
atmosphere, a few metres below the surface of the lake.
So the problem refers to a physiological adjustment... but a SHORT-
TERM one.... NOT a relatively long-term one, like blood-cell count changes.
*With regard to NITROX, it would reduce the problem while under
water, while still breathing Enriched Air (or pure O2), but may occur
when the diver took his first breaths on the surface.
It's the sudden reduction in available O2 (especially to a point quite
close to hypoxic levels) may not allow a diver to sustain anything but low
exertion levels, ... at least until his (sorry..OR HER), circulation and
metabolisim have picked-up a bit.
Hope this helps..
Regards, Bernie Woolfrey
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