"T o d d P a t t i s t" wrote in message
"Ian Johnston" wrote:

: Of course, at high altitudes, if the PP of CO2 is so low
: that your body fails to breathe, then that can cause of
: death, even if the PP of O2 would be high enough to keep you
: alive.

That's what I ws thinking of. Doesn't that effect kick in about thirty
something thousand feet?

It's no lower than that, and is typically higher. I'm not
sure of the actual point.

That the breathing response is diminished? It starts much lower. But the
rest of your post indicates that you agree with that.
I've been through the
FAA/military oxygen training 3 times and I've flown to 30K'
in a glider on 100% diluter demand O2. I was breathing
deeply and carefully under conscious control, not relying on
my breathing reflex.

That's a real feat. Without acclimatisation training, which, among other
things, increases hemoglobin counts, it's hard to stay usefully awake after
a rapid ascent to that altitude. If you used an oximeter, I'd be interested
in the readings. Did you notice any of the usual effects of hypoxia?

moo