Passing out at high altitudes / the Greek ailrliner crash

I am not a pilot, and as much as my email address sounds like I am a
doctor, I'm not...

That said, I thought someone here might be able to help me out - they
news reports talk about passing out within seconds at high altitudes.
I understand the air is thinner / less O2.

But if I go underwater, there's certainly no air there. And I can stay
down for a while, holding my breath. How is high altitudes different?
I would think you would rasp / fight to breath in but keep functioning
as your body uses up the 02 in the blood from your last breath? Not
like a sleeping gas in the movies where you just keel over as soon as
it hits you?

THANKS!

On 8/15/2005 09:54, wrote:

I am not a pilot, and as much as my email address sounds like I am a
doctor, I'm not...

That said, I thought someone here might be able to help me out - they
news reports talk about passing out within seconds at high altitudes.
I understand the air is thinner / less O2.

But if I go underwater, there's certainly no air there. And I can stay
down for a while, holding my breath. How is high altitudes different?
I would think you would rasp / fight to breath in but keep functioning
as your body uses up the 02 in the blood from your last breath? Not
like a sleeping gas in the movies where you just keel over as soon as
it hits you?

THANKS!


There is a big difference between Air and Oxygen. With no Air,
you are unable to move your lungs (there is nothing to pull in).

With low oxygen, you can still move air, it just don't provide the
oxygen necessary to support your life.

This is called Hypoxia, and one of the side effects of this is
euphoria. What that means, is it causes you to feel like everything
is really great, when in fact, you're asphyxiating yourself.

Here is a link to an explanation of Hypoxia:

http://www.batnet.com/mfwright/hypoxia.html

This is the simple answer. Let me know if you would like more details.


--
Mark Hansen, PP-ASEL, Instrument Student
Sacramento, CA

My understanding is that the O2 in the cells and in the blood will actually
go back into the lungs at very low ambient pressures. It doesn't matter
whether you breath or hold your breath, the O2 will leave your body. It is
something like the bends where gases that will disolve in the body under
higher pressures will come out of solution at lower pressures.

Mike
MU-2


wrote in message
oups.com...
I am not a pilot, and as much as my email address sounds like I am a
doctor, I'm not...

That said, I thought someone here might be able to help me out - they
news reports talk about passing out within seconds at high altitudes.
I understand the air is thinner / less O2.

But if I go underwater, there's certainly no air there. And I can stay
down for a while, holding my breath. How is high altitudes different?
I would think you would rasp / fight to breath in but keep functioning
as your body uses up the 02 in the blood from your last breath? Not
like a sleeping gas in the movies where you just keel over as soon as
it hits you?

THANKS!

It isn't totally clear from your post but I think you have it wrong. The
concentration of O2 is the same at all altitudes. At 18000' for instance
the air pressure is half, the concentration of O2 is the same as at sea
level so the total amount of O2 is half.

Mike
MU-2


"Mark Hansen" wrote in message
...
On 8/15/2005 09:54, wrote:

I am not a pilot, and as much as my email address sounds like I am a
doctor, I'm not...

That said, I thought someone here might be able to help me out - they
news reports talk about passing out within seconds at high altitudes.
I understand the air is thinner / less O2.

But if I go underwater, there's certainly no air there. And I can stay
down for a while, holding my breath. How is high altitudes different?
I would think you would rasp / fight to breath in but keep functioning
as your body uses up the 02 in the blood from your last breath? Not
like a sleeping gas in the movies where you just keel over as soon as
it hits you? THANKS!


There is a big difference between Air and Oxygen. With no Air,
you are unable to move your lungs (there is nothing to pull in).

With low oxygen, you can still move air, it just don't provide the
oxygen necessary to support your life.

This is called Hypoxia, and one of the side effects of this is
euphoria. What that means, is it causes you to feel like everything
is really great, when in fact, you're asphyxiating yourself.

Here is a link to an explanation of Hypoxia:

http://www.batnet.com/mfwright/hypoxia.html

This is the simple answer. Let me know if you would like more details.


--
Mark Hansen, PP-ASEL, Instrument Student
Sacramento, CA

In article .com,
wrote:

I am not a pilot, and as much as my email address sounds like I am a
doctor, I'm not...

That said, I thought someone here might be able to help me out - they
news reports talk about passing out within seconds at high altitudes.
I understand the air is thinner / less O2.

But if I go underwater, there's certainly no air there. And I can stay
down for a while, holding my breath. How is high altitudes different?

It depends on how you get there :-)

If the decompression is sudden then you can't "hold your last breath."
If you try then the air pressure in your lungs will cause them to
rupture. It's called an "air embolism". Scuba divers can get them too
if they surface while holding their breath.

If the decompression is slow then you can keep breathing but your blood
oxygen level will gradually go down and you will gradually lose mental
function. The effect can be subtle enough that you don't realize that
it's happening even as you drift into unconsciousness. Pilots sometimes
get special training to help them recognize and deal with the symptoms
of decreased blood oxygen at high altitude.

In a sudden decompression it is of course obvious that something has
happened, but your "time of useful consciousness" as it's called can be
very short (seconds). If you don't manage to put on an oxygen mask in
that time, or if the oxygen system isn't working, you drift off to sleep.

There is one case of a pilot who actually managed to survive such an
occurrence. The plane was on autopilot when the (human) pilot passed
out and when it ran out of gas the autopilot kept the wings level and
the plane did a gear-up landing in a field.

rg

On 8/15/2005 10:29, Mike Rapoport wrote:

It isn't totally clear from your post but I think you have it wrong. The
concentration of O2 is the same at all altitudes. At 18000' for instance
the air pressure is half, the concentration of O2 is the same as at sea
level so the total amount of O2 is half.

Yes, you're right (on both counts) - I had forgotten about this.


Mike
MU-2


"Mark Hansen" wrote in message
...
On 8/15/2005 09:54, wrote:

I am not a pilot, and as much as my email address sounds like I am a
doctor, I'm not...

That said, I thought someone here might be able to help me out - they
news reports talk about passing out within seconds at high altitudes.
I understand the air is thinner / less O2.

But if I go underwater, there's certainly no air there. And I can stay
down for a while, holding my breath. How is high altitudes different?
I would think you would rasp / fight to breath in but keep functioning
as your body uses up the 02 in the blood from your last breath? Not
like a sleeping gas in the movies where you just keel over as soon as
it hits you? THANKS!


There is a big difference between Air and Oxygen. With no Air,
you are unable to move your lungs (there is nothing to pull in).

With low oxygen, you can still move air, it just don't provide the
oxygen necessary to support your life.

This is called Hypoxia, and one of the side effects of this is
euphoria. What that means, is it causes you to feel like everything
is really great, when in fact, you're asphyxiating yourself.

Here is a link to an explanation of Hypoxia:

http://www.batnet.com/mfwright/hypoxia.html

This is the simple answer. Let me know if you would like more details.


--
Mark Hansen, PP-ASEL, Instrument Student
Sacramento, CA




--
Mark Hansen, PP-ASEL, Instrument Student
Sacramento, CA

wrote:
: But if I go underwater, there's certainly no air there. And I can stay
: down for a while, holding my breath. How is high altitudes different?
: I would think you would rasp / fight to breath in but keep functioning
: as your body uses up the 02 in the blood from your last breath? Not
: like a sleeping gas in the movies where you just keel over as soon as
: it hits you?

Your breathe reflex is controlled by the concentration of CO2 in your blood,
not the lack of O2. If you hold your breath underwater, you increase CO2
concentration and your breathe reflex kicks in. If you go to high altitude (or
breathe any non-CO2-enriched mixture of gasses where the partial pressure of O2 is too
low to maintain adequate O2 transfer to your blood), the CO2 in your blood will
happily exchange out of your lungs. You don't feel the urge to breathe, and simply
pass out from lack of oxygen.

Different mechanisms between life-sustainment and breathe reflex.

-Cory

--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

Not quite. Mole fraction of oxygen in the air is the same at all
altitudes, about 21%. Concentration, in the senses of partial pressure
and number of molecules in a given volume (such as one breath), goes
down with increasing altitude. The partial pressure translates to the
fraction of available molecules that are biologically usable; the
density of molecules translates to how many there are in the breath.
You lose twice with increasing altitude.

David

Mike Rapoport wrote:
It isn't totally clear from your post but I think you have it wrong. The
concentration of O2 is the same at all altitudes. At 18000' for instance
the air pressure is half, the concentration of O2 is the same as at sea
level so the total amount of O2 is half.

Mike
MU-2

Based on my experience in a USAF altitude chamber, after the chamber has
been pumped up (actually down...it is a vacuum) to 25000 feet and the
pressure suddenly dumped as would be the case in a decompression, whatever
air you have in your lungs comes out forcefully...no way do you have any
control over it. Gotta get that mask on and get it on in a hurry, because
time is fleetingly short.

In US regulations, the magic altitude is flight level 350 (more or less
35000 feet, depending on ambient atmospheric pressure). The Cypriot plane
was reportedly at FL 340, if we can believe the media. Under US rules, above
FL 350 both pilots must be at the controls and each must have a
quick-donning mask at hand. If one pilot has to leave the cockpit for any
reason, the other has to put on and use oxygen until he returns.

Lots of unknowns.

Bob Gardner


Bob Gardner

wrote in message
oups.com...
I am not a pilot, and as much as my email address sounds like I am a
doctor, I'm not...

That said, I thought someone here might be able to help me out - they
news reports talk about passing out within seconds at high altitudes.
I understand the air is thinner / less O2.

But if I go underwater, there's certainly no air there. And I can stay
down for a while, holding my breath. How is high altitudes different?
I would think you would rasp / fight to breath in but keep functioning
as your body uses up the 02 in the blood from your last breath? Not
like a sleeping gas in the movies where you just keel over as soon as
it hits you?

THANKS!

Bob Gardner wrote:

Based on my experience in a USAF altitude chamber, after the chamber has
been pumped up (actually down...it is a vacuum) to 25000 feet and the
pressure suddenly dumped as would be the case in a decompression, whatever
air you have in your lungs comes out forcefully...no way do you have any
control over it. Gotta get that mask on and get it on in a hurry, because
time is fleetingly short.

In US regulations, the magic altitude is flight level 350 (more or less
35000 feet, depending on ambient atmospheric pressure). The Cypriot plane
was reportedly at FL 340, if we can believe the media. Under US rules, above
FL 350 both pilots must be at the controls and each must have a
quick-donning mask at hand. If one pilot has to leave the cockpit for any
reason, the other has to put on and use oxygen until he returns.

It's FL 250 (121.333 I believe). Above 250 one crewmember must be on O2 when
the other leaves the flight deck.

As to decompression of an aircraft the size of the 737, there is rapid
decompression and explosive decompression. It the packs both trip off or a
window blows out it results in rapid decompression, which is quite different
than an altitude chamber experience. The cabin ascends at perhaps 10,000 feet
per minute. But, if there is some type of structural failure resulting in a
whole larger than a window, then the cabin can explosively decompress, similar
to your experience in the altitude chamber.