The useful consciousness time as it reaches its high-altitude minimum is mostly the transit time of the already oxygenated blood that just left your lungs on the way to the brain at the "moment" of pressure loss--when that low oxygen blood gets there, your conscious brain cells, which have some of the most rapid replenishment rates of any tissue in the body, go to sleep almost immediately.

Ok, so why don't I collapse right away after taking a breath of helium
to talk like Donald Duck?

And...btw... this is a perfect example of why I trim newsgroups. I
originally sent this as a "reply", as I was told to do by people here
who have some issue with my trimming groups and/or indicating which ones
I follow.

My newsreader is dumb.

The reply went =only= to alt.disasters.aviation, where I will never see
a reply and will probably be accused of hit and run posting, an
accusation I will also never see. Followups had been set to that group,
and I didn't catch that. I don't follow that group. But discussion
seems to be happening here too.

My newsreader is dumb.

So now I'm replying manually here only, so that if there is a reply,
I'll actually see it.

Jose
p.s. My newsreader is dumb.
--
Quantum Mechanics is like this: God =does= play dice with the universe,
except there's no God, and there's no dice. And maybe there's no universe.
for Email, make the obvious change in the address.