jmk wrote:
It is still possible to pass out from Hypoxia without building up CO2
levels back to the amount needed to trigger the chemoreceptors to tell
your brain "I GOTTA BREATHE". It has been the cause of more than one
drowning/diving accident.


Some years back I saw a GREAT film on this. They take several guys,
just sitting on a couch, and hook them up to full face masks, bypassing
a CO2 scrubber, and an auxilliary air cannister. So they can just sit
there and breathe normally.

Normally, it is the CO2 levels that tell you to breath. How ever those
with chronic obstructive disease (emphasema, long term bronchitis,
etc...) have so much CO2 in their system on a regular basis, that their
body switches to using the O2 levels (hypoxic drive) to control their
breathing. These folks you can put into respiratory arrest giving them
100% oxygen.