Colony ship to Alpha Centauri - The Motion Picture Concept b

I've just done a little anecdotal-grade experiment. Everybody's done the
"how long can you hold your breath" trick, with some people achieving
three or four minutes. But I thought, in vacuum, you don't have a
lungful
of air. How closely can I simulate that condition by just simply
exhaling
as hard, and completely, as I can?

So I did. I exhaled, and continued to exhale, forcing all of the air
out
of my lungs that I was able to - since I'm in the atmosphere, there will
obviously be some quantity of air remaining. Oh, well, we'll have to
adjust our parameters. So I squeezed out as much as I could, and started
watching the clock.

At 45 seconds, I was impelled to breathe. I'm sure I could have gone
longer, but the "BREATHE NOW!" imperative from my limbic system was more
powerful than my desire to see if I got a buzz from it.

I guess the point is, you'd probably stay conscious for more than 15
seconds, but it would, like, hurt, like being strangled or something.
Shudder!

Unfortunately, your simulation didn't really match vacuum conditions very
well. The major difference is that when your lungs are full of nothing,
gases in the blood will actively *escape* back out into the lungs. The
blood going through your lungs will not only not be re-oxygenated, it will
be very efficiently de-oxygenated. The 15 seconds of consciousness comes
from the fact that this is about how long it takes blood to get from your
lungs to your brain. Once blood that's had all of the oxygen sucked out of
it reaches your brain, it's game over as far as remaining conscious goes.

I guess the point is, you'd probably stay conscious for more than 15
seconds, but it would, like, hurt, like being strangled or something.
Shudder!