From: sbharris@ix.netcom.com (Steven B. Harris )
Subject: Re: Info needed high altitude effects
Date: 01 Oct 1995
Newsgroups: sci.med

In <812552968.2985@dibbler.demon.co.uk> Peb <peb@dibbler.demon.co.uk>
writes:

>I would like to obtain information on high altitude aircraft
>and the effects of high altitude on the human body.
>e.g. how high can an aircraft fly? Problems of personnel
>escaping from aircraft at high altitude. What effects does
>high altitude have on the unprtotected human body? This latter
>point may sound a silly question but I would like a break down
>of the conditions that lead to death. What would be needed in
>order for somebody to survive a high altitude ejection?
>
>If you know of any information sources that would help please
>e-mail me.
>Thanks.
>
>Tricia Bond
>University of Manchester
>Undergrad.


   Tricia, your nearest medical library probably has a section on
aerospace medicine, which is concerned exactly with all the topics you
address here.  It's WAY too much to answer this way.  In general, many
advanced reconnaisance airplanes (like the SR-71) and experimental
rocket planes (like the famous X-15) are/were capable of flying high
enough that you need a full spacesuit to survive when ejecting from
one.   This is because, over about 45,000 feet, there isn't enough
pressure even breathing pure oxygen to keep you alive.  Full pressure
suit = space suit. (not to be confused with pilot g-suits, which merely
squeeze blood from legs and abdomen into the head during
acceleration).

   At very high altitude, the effect of sudden depressurization is
interesting.  Neither people or animals "explode."  Instead, people
exhale involuntarily, since neither chest or lungs is strong enough to
maintain much pressure difference between inside and outside the body.
After that, blood being pumped through the lungs instantly is
desaturated of oxygen, since the oxygen transfer in the lungs is not
active, but passive, and works just as well in reverse.  When this
desaturated oxygen-less blood gets through the lungs and then hits the
heart, the heart stops within seconds, not having any fuel.  This
happens so fast that in the dog experiments mimicking explosive
decompression onboard Apollo spacecraft in space (sudden decompression
from 1/3 atmosphere pure O2), the heart stopped so fast that
unoxygenated blood didn't even make it all the way down the aorta
before circulatory arrest.  With circulatory arrest, unconsciousness
follows within about 10 seconds (giving you a total of maybe 15 seconds
of useful consciouness with which to rue your bad luck).  People in
cardiac arrest are resuscitatable for some time after that (5 minutes,
perhaps), but that takes full equipment, and doesn't happen
spontaneously.  A pilot caught in a very high altitude bailout without
a p-suit would continue in circulatory arrest, and be dead long before
hitting the ground under a parachute.

  Bailouts between about 18,000 and about 35,000 feet can be done with
a good oxygen mask and a bottle of oxygen, which is supplyed in the
average jet pilot's equipment.  Under these circumstances, the pilot
"free-falls" through the pressure zone requiring mask oxygen in less
than 2 minutes, and indeed MUST do this before opening his chute
(otherwise he risks running out of oxygen, and/or freezing).

                                               Steve Harris, M.D.

From: gee@hermes.dciem.dnd.ca (Thomas Gee)
Subject: Re: Info needed high altitude effects
Date: 02 Oct 1995
Newsgroups: sci.med

In article <44mqn3$cv9@ixnews7.ix.netcom.com>,
Steven B. Harris  <sbharris@ix.netcom.com> wrote:

>			With circulatory arrest, unconsciousness
>follows within about 10 seconds (giving you a total of maybe 15 seconds
>of useful consciouness with which to rue your bad luck).  People in
>cardiac arrest are resuscitatable for some time after that (5 minutes,
>perhaps), but that takes full equipment, and doesn't happen
>spontaneously.  A pilot caught in a very high altitude bailout without
>a p-suit would continue in circulatory arrest, and be dead long before
>hitting the ground under a parachute.

Fortunately, there is something you can do about this.  Over a decade ago,
our institute designed a positive-pressure breathing life support system
called COMBAT EDGE, which is just now being installed into USAF F-15 and
F-16 aircraft.

This system protects both against high-G and high-altitude without
a pressure suit (which is difficult to fit in a fighter).  Like Steve
said, above 35,000 feet even pure O2 is not sufficient to maintain
"useful consciousness" (I've always liked that term), for there are too
few oxygen molecules in the lungs to pass into the bloodstream (lack of
partial pressure).

So, the secret is to force oxygen into the lungs at higher than ambient
pressures.  As designed, our system could provide up to 80 mmHg
(millimeters of mercury, or roughly 1.6 psi, or 1/10th of an atmosphere)
of pressure above ambient levels.  This is a little less than the pressure
you can generate in your lungs by suppressing a good sneeze.

Unfortunately, this much force will tend to overexpand the lungs, so
the pilots wear a tight upper body jerkin to keep their ribcage in.
Also it is very difficult to breathe out against this much pressure,
so inflated bladders are installed in the jerkin which equalize the
pressure inside and outside the chest area, and make it much easier to
breathe.

So, now you have 80 mmHg pressure in the lungs pushing out, and 80 mmHg
in the jerkin bladders pressing in.  The result?  The blood in your
chest cavity rushes down to your feet and hides there.

Fortunately, this is the same problem we encounter at high G levels.
So the pilot also wears an anti-G suit, which squeezes the legs and
lower abdomen, and forces the blood back up to where it can do some good.

This system can maintain useful consciousness for at least two minutes
at 60,000 feet, which is the time required to fly a jet fighter back down
to a safe altitude.  We've used it successfully as high as 80,000 feet in
the past, and 72,000 feet in recent experiments.

We use an altitude chamber for testing these systems, and I have been a
subject/victim for quite a few explosive decompression tests that we've
done in them.  Someday I'll write it up and post it.  My life as the
Michelin[tm] Tire Man.

>                                               Steve Harris, M.D.

Tom
--
 Thomas Gee      \   altitude      \ Aerospace Physiology Software Development
 gee@dciem.dnd.ca \   acceleration  \  DCIEM, CFB Toronto, North York, Ontario
                   \   automation    \   Department of National Defence/Canada

From: gee@hermes.dciem.dnd.ca (Thomas Gee)
Subject: Re: Info needed high altitude effects
Date: 03 Oct 1995
sender: gee@dciem.dnd.ca (Thomas Gee)
Newsgroups: sci.med

In article <44prj6$3q6@ixnews3.ix.netcom.com>,
Steven B. Harris  <sbharris@ix.netcom.com> wrote:

>In <44pg2u$j2g@mozart.dciem.dnd.ca> gee@hermes.dciem.dnd.ca (Thomas Gee)
>writes:
>
>>This system can maintain useful consciousness for at least two minutes
>>at 60,000 feet, which is the time required to fly a jet fighter back
>>down to a safe altitude.  We've used it successfully as high as 80,000
>>feet in the past, and 72,000 feet in recent experiments.
>>
>>We use an altitude chamber for testing these systems, and I have been a
>>subject/victim for quite a few explosive decompression tests that we've
>>done in them.  Someday I'll write it up and post it.  My life as the
>>Michelin[tm] Tire Man.
>
>   Comment:  Damn, that's neat!  Sounds a bit Rube Goldberg, but then so
>does everything else that's new.  If it works, it works.

Heh.  You should see what the new (highly experimental) system looks like.
It's all ungainly wires and computers and shiny metal bits with glowing
LED's.

I've always gotten a chuckle out of movie scenes where research
institutes, particularly military ones, are huge grim places with odd
indirect lighting and gothic walls and pillars, or they're
brilliantly-lit white cubicals with neatly integrated panels of flashing
lights.

In my experience, research labs are marked by two things: vast amounts of
wire and millions of scattered bits of paper with esoteric scribblings on
them.

>Just be glad you're in the military and aren't trying to get FDA approval
>for it.
>Can you imagine what they'd say about the danger of pulmonary gas
>embolism?  I suppose you check all your pilots for loose foramen ovale
>flaps, as they do for divers?

Loose whats?   :-)

Well, to be fair all pilots and experimental subjects need to pass an
extensive physical every year, so we know that they have a minimal number
of loose body parts.

>   Let me see: 80 mm of Hg absolute O2.  That's quite enough to give you
>good sats.  How long can you maintain yourself in total vacuum with
>this?  Has anybody ever dared try it?

Actually, we have taken it as high as 80,000 feet.  Now, that's ..umm..
20.8 mmHg ambient pressure, which is equivalent to less than 3% of sea-
level pressure.  It is likely that there is no physiological difference
between 3% of an atmosphere and total vacuum.

But then, I'm not a physiologist, so take that thought with a grain of
salt.

The problem with hanging out at these altitudes is decompression sickness.
The nitrogen comes out of solution in your blood and forms bubbles, and
this is not a Good Thing.  In the lab, we pre-breathe 100% O2 for an hour
before the experiment to reduce the risks, but this is may not be an
option for the pilots.  But if the pilot needs this sort of altitude
protection, getting the bends will not be their greatest worry, so I guess
the risks are all relative.

Tom
--
gee@dciem.dnd.ca
Aircrew Performance/Protective Section
Aerospace Life Support Technology Sector

From: sbharris@ix.netcom.com (Steven B. Harris )
Subject: Re: Info needed, high altitude flying/decompression
Date: 04 Oct 1995
Newsgroups: sci.med

In <8B262E3.0509009D78.uuout@imagine.pt> jx@imagine.pt (JOAO MAGALHAES)
writes:

>>Can you imagine what they'd say about the danger of pulmonary gas
>>embolism?  I suppose you check all your pilots for loose foramen ovale
>>flaps, as they do for divers?
>
>TG>Loose whats?   :-)
>
>Loose flaps -- You can't fly with loose flaps :-))


   They check military divers for atrial septal defects (ASD) by
cardiac echo, because during decompression the gas bubbles in the blood
are mostly filtered out by the pulmonary bed, and do little harm.  In
people with ASD's however, those bubbles bypass the pulmonary bed and
get into the systemic arterial circulation, where they embolize thinges
like your brain then they hit the arterioles and can go no further.
That's bad.

   A special class of people (something like 20%? if memory plays no
tricks on me) have a closed foramen ovale between the two atria (as is
normal), BUT the flap has not sealed when it closed shortly after birth,
so they get an ASD shunt whenever they get pulpunary hypertension (such
as a during the "ram the oxygen down your lungs under pressure
experiment" being described), and right heart atrial pressures
temporarily exceed left atrial return pressures.  I don't know if this
happens with these weird high altitude suits, or if there's any way to
screen for this in test subjects.  But I hope somebody has thought of
it.  The best thing would be for the Airforce aerospace medicine docs to
talk to the Navy diving docs to see what kind of cross fertilization of
knowledge occurs.

   Anyway, I'm AMAZED at the progress being made here.  We're talking
about a rubber contraption that will keep a man alive and functional for
a few minutes in hard vacuum-- no spacesuit required.  If anybody here
has read the classic Arthur C. Clarke story about the spaceship full of
people who had to escape to another ship nearby with no pressure suits,
you realize how advanced this idea is.  NOBODY has predicted this in
science fiction, and that's the SF writer's job.

                                          Steve Harris, M.D.

From: hedgehog@cais.com (Robert R. Fenichel)
Newsgroups: sci.med.cardiology
Subject: Re: patent foramen ovale
Date: Thu, 01 Aug 1996 02:30:15 GMT

dozer.1@pop.service.ohio-state.edu (David Dozer) wrote:

>I had a transesophageal echocardiogram performed with simultaneous TCD  
>resulting with evidence of patent foramen ovale, mostly during shunt during 
>Valsalva maneuver.  The remainder of the study is normal.
>
>This test was performed to try and detect this result.  The reason is that 
>there appears to be a high correlation between a PFO and decompression 
>sickness from diving.  I was a commercial diver, and was getting bent.
> The only thing I know about this condition 
>(and at the time it was all I wanted to know) is that I'm not suppose to dive.

  Decompression sickness happens when nitrogen, dissolved in your
blood at high pressure, starts coming out of the blood and forming
little bubbles when the pressure is reduced.  The bubbles can be a
problem because until they get reabsorbed and exhaled away, they can
wedge in a blood vessel and prevent circulation from getting beyond
that point.

  Most such bubbles form on the venous side of the circulation, so
they flow downstream through larger & larger veins to the right side
of the heart, shoot out towards the lung, and (usually) wedge in the
lung where conditions are favorable for the nitrogen to equilibrate
from the blood space to the air space, and to go away.  The blood
continues from the lungs to the left side of the heart and thence out
to the arteries and the body.

  Some bubbles form on the arterial side, and they can wedge in joints
or the brain or other organs, giving you problems.  Thats what the
Bends is.

  Before birth, the heart goes through a complex pattern of
development, and for much of that time there is are connections
between the right side of the heart and the left side.  The blood then
has no reason to go through the lungs, and it doesn't.  One of the
usually-temporary right --> left connections is the foramen ovale (=
oval hole).  

  In people like you in whom the FO fails to close, bubbles (or other
debris) from the venous circulation can sneak across to the arterial
side without being filtered by the lungs.  That is, your risk of
serious decompression sickness (not just aches & pains; I'm talking
about permanent neurological damage, heart attacks, and death) is
greater than that of the next person.

  Open FOs are sometimes closed surgically.  I don't know if that's
ever done in someone whose only problem is inability to tolerate
compression/decompression.

                                            Robert R. Fenichel, M.D.

From: sbharris@ix.netcom.com (Steven B. Harris )
Subject: Re: Info needed high altitude effects
Date: 06 Oct 1995
Newsgroups: sci.med

In <453mmo$cnu@brahms.dciem.dnd.ca> gee@hermes.dciem.dnd.ca (Thomas
Gee) writes:

>In article <451aa5$hp0@ixnews6.ix.netcom.com>,
>Steven B. Harris  <sbharris@ix.netcom.com> wrote:
>
>>How long does it take him to get below 14,000 feet?  Right, less than
>>30 seconds.  During that time, how much is his performance degraded?
>>Could you even find penmanship differences after 30 seconds of this
>>kind of slight hypoxia?  I doubt it.
>
>Very minimal, although his judgment will be impaired before his writing
>is. However, after an ejection, the ejectee is not required to make any
>decisions until just before landing. Everything else is automatic.
>
>> 					    People can raise families
>>at 15,000, and work every day above 17,000.  A number of people have
>>now made it to the summit of Everest at 29,000 feet without an oxygen,
>>and one physician has even drawn blood gas samples on himself at that
>>altitude.
>
>Interesting.  For our pilot training, we take people up to 22,000 feet
>in the altitude chamber.  They are breathing 100% oxygen until they
>reach altitude.
>
>Once they get up there, they remove their masks, and begin the
>aforementioned handwriting test, where they reproduce simple
>drawings (a square, a star, a circle) repeatedly until they feel
>that they have been compromised.  At that point they reconnect to
>their oxygen system.
>
>The last time I did this test (for a Discovery television show), I
>had been off oxygen for four and a half minutes when I decided to
>"reconnect", a task consisting of connecting my mask to the oxygen
>tube, and flipping two switches on the regulator.  I got the first
>connection done though it took 5-10 seconds longer than it should
>have.  But when it came to flipping the two switches, I dabbed
>helplessly at them until an aeromedical technician came over and
>helped me.
>
>(This was captured on video tape, and I saw it afterwards.  At the
>time, nothing seemed amiss in my reconnection, although I remember
>that moving the two switches was oddly tricky.  And I don't remember
>being helped with them.)
>
>Hypoxia is an insidious thing, and can seriously impair your judgment
>well before any gross effects become obvious.  That is why we do
>these tests, so that people can recognize the early effects and
>deal with them while they still have the functioning neurons.
>
>Tom
>--
>gee@dciem.dnd.ca
>Aircrew Performance/Protective Systems Section
>Aerospace Life Support Technology Sector



   Comment:  God yes.  Otherwise they'd come out of your chamber as New
Democrats.  Horrible.

                                              Steve Harris, M.D.