From: sbharris@ix.netcom.com(Steven B. Harris)
Newsgroups: sci.physics
Subject: Re: Exploding Fish
Date: 29 Nov 1998 08:01:03 GMT

In <19981129003857.02550.00001378@ng57.aol.com> yodadawg@aol.com
(YodaDawg) writes:

> what would happen if a shace shuttle astronaut were to
>open the shuttle doors and jump out into space wearing nothing but his
>boxer shorts?  Is the pressure differencial enough to make the
>astronaut explode?


 No.

>What would happen to the unprotected astronaut's body?


   Nothing much.  He or she would suffer an explosive caugh/expiration,
perhaps pass some bowel gas, and lose consciousness in about 15 seconds
(time for deoxygenated blood from the lungs to reach the heart, the
heart to stop).  The brain quits functioning from zero blood pressure
or zero blood oxygen in about five seconds, and it's a toss-up as to
which happens first in sudden decompression.  In experiments with dogs
explosively decompressed from 1/3rd atmosphere pure O2 to vacuum (part
of the Apollo program science), the heart stopped SO fast from
deoxygenated blood hitting it, that the wave of deoxygenated blood
didn't even have time to make it all the way down the aorta.  That
suggests it barely reaches the brain also.

   Note that even when unacclimatized you can get by on 50 Torr O2
partial pressure for awhile (long enough to maintain consciousness for
some minutes), and as it happens, your lungs can sustain a differential
of 50 Torr (roughly 1/15th atm) with help, without giving you gas
embolism (real problem at higher differential pressures).  So if that
50 Torr is pure oxygen, you can actually get by in vacuum for a bit
(your eyeballs start to dry out and other nasty things, but at least
you're not DYING).  You need a constrictive chest piece to help keep
you lungs pressurized all the time, and a really tight fitting facemask
that forces tidal volumes at this differential, sort of like a
continuous positive airway pressure (CPAP) device for snorers.  This
keeps you from having to suck so hard with the darned chest compressor
trying to squeeze you out.  This kind of thing is being tested in lieu
of full pressure suits for bailouts at EXTREMELY high altitudes, and
believe it or not, the Rube Goldberg thing actually works in pressure
chamber tests.  If your shuttle astronaut was wearing one of these, he
or she could spend a five or ten uncomfortable minutes trying to get
back in the spaceship, even in boxer shorts and bare feet and hotel
bathrobe.  Hal, open the door.  Hal!  If not, and he bailed out with
lungs full of pure O2 and was VERY dexterous at being able to exhale
enough to prevent gas embolism, but stop at 50 Torr, and do a Valsalva
maneuver (expiration against a closed glottus to keep chest
differential pressure high), he might be able to extend his duration of
consciousness another minute, until the oxygen stored in his blood gave
out.

                                           Steve Harris

From: Steven B. Harris <sbharris@ix.netcom.com@ix.netcom.com>
Newsgroups: sci.med
Subject: Re: Effects of Breathing Nitrogen at Altitude
Date: Thu, 21 Dec 2000 08:58:08 GMT

In article <Pine.SGI.3.96.1001218164001.14233995A
100000@mole.bio.cam.ac.uk>,
	Bennett <njb35@mole.bio.cam.ac.uk> wrote:


>At high altitude though, the air pressure is so low that the O2 will come
>rushing out of your blood, rather than the opposite direction.  You then
>have just enough time for that deoxygenated blood to reach your brain
>before you drop off...  This is different from a breath hold in that the
>oxygen will start off leaving the alveolar air, and then simply
>equilibrate (ie the rate of uptake will drop off until zero) - it won't
>actually deoxygenate your blood.
>
>That's how I think of it anyway, based on 1st year physiology ;-)
>
>Bennett

You are quite correct. That is exactly what happens. You cannot hold
your breath against more than about 2 psi of lung overpressure without
severe danger of lung rupture and arterial gas embolism. And 2 psi of
air is not even close to enough to sustain consciousness.

As you guessed, the problem is that the lungs are a completely passive
and non-directional gas exchanger, and they work just as well to
deoxygenate the blood as to oxygenate it.  About all the time you get
with an explosive decompression where you go to 10% or less of normal
pressure, is the time it takes for the deoxygenated blood to hit your
heart and stop it (which is just about the time it hits your brain, so
it's rather hard to tell whether you black out from hypoxia or loss of
blood pressure). In dog experiments done for the Apollo program, which
went from 5 psi pure oxygen to vacuum in a few seconds, the deoxygenated
blood didn't even make it completely down the aorta before full cardiac
arrest occurred. So forget bouncing around in the airlock, ala Dave
Bowman of 2001, twittling switches. You're out like a light. You might
still be resuscitable for 4-8 minutes or whatever (depending on your
technology), but it'll be somebody else doing it. It certainly won't
happen spontaneously once the heart stops.