"Ian Johnston" wrote in message
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 starts at about 14,000 feet. People sleeping above this altitude can
suffer a condition called "Periodic Breathing". This is a cycle of
breathing until CO2 levels drop (the body enters a state of alkalosis), then
breathing stops, CO2 levels rise, the body responds by gasping and
hyperventilating and then stops breathing again. As altitude goes up, the
effect becomes nastier. And a bunch of other bad things become a looming
possibility.

le m