Oxygen above 20,000 feet

wrote:

Hey dave,
Ever swam under water?
Ever hypervent your self before taking that last breath so you can stay
down longer?
What would you call that?


You are eliminating the Carbon Dioxide in your body to VERY low levels,
which helps forestall the URGE to breath until they build back up to
higher levels.

Hyperventilation does not increase oxygen capacity over and above what
normal breathing does. It simply clears out waste products. All of this
is again a function of the partial pressures and pressure gradients that
were discussed elsewhere in this thread.

On room air, your pO2 in arterial blood is in the area of 80-100 mmhg.
Your pC02 is in the neighborhood of 40 mmhg. Oxygen Saturation is in the
90-100% range.

Mixed venous blood gases (which are sampled from the pulmonary artery,
in patients with the proper monitoring equipment) on room air tends to
be in the 40-50 mmHg range. This corresponds with about ONE of the FOUR
oxygen molecules on each hemoglobin molecule being extracted, and a
saturation in the 60-75% range. Without a fresh supply of oxygen in the
lungs to extract from, this "desaturated" blood makes a second trip
around, and because of the laws of nature, it is even more difficult for
the remaining oxygen to be extracted. For practical purposes, its
essentially NOT going to release more than two of the four
hemoglobin-bound oxygen molecules. Your arterial oxygen saturation gets
too low and you will end up getting confused, euphoric, or just unconscious.

Hyperventilation in an otherwise healthy individual will not increase
the p02, but can/will drive the pCO2 in arterial blood down to the 20's.
Prolonged hyperventilation will cause vasoconstriction in the brain
(as well as everywhere else), resulting in lightheadedness, dizziness,
cramping in the fingers/toes, and chest pain. I deal with persons on
breathing machines EVERY DAY for a living. If their oxygen level is low,
we dont turn up the rate or volume, we turn up the oxygen concentration.
If their CO2 level is high, THEN we turn up rate/volume to increase
the amount of VENTILATION. Ventilation is the removal of waste products.
Oxygenation is the delivery of oxygen. They are TWO completely different
functions, and not very related to each other, despite the fact they are
happening in the same place at the same time.

It is still possible to pass out from Hypoxia without building up CO2
levels back to the amount needed to trigger the chemoreceptors to tell
your brain "I GOTTA BREATHE". It has been the cause of more than one
drowning/diving accident. If you want further reference on this, a
knowledgeable professional diver, an aerospace medicine MD or a
hyperbaric technician should be able to validate this information.

Dave

Once in a while you get these little gems that are worth filing in the ol'
grey matter. The rest of the time, I run the usenet shredder almost
continuously.

"Dave S" wrote in message
k.net...


wrote:

Hey dave,
Ever swam under water?
Ever hypervent your self before taking that last breath so you can stay
down longer?
What would you call that?


You are eliminating the Carbon Dioxide in your body to VERY low levels,
which helps forestall the URGE to breath until they build back up to
higher levels.

Hyperventilation does not increase oxygen capacity over and above what
normal breathing does. It simply clears out waste products. All of this is
again a function of the partial pressures and pressure gradients that were
discussed elsewhere in this thread.

On room air, your pO2 in arterial blood is in the area of 80-100 mmhg.
Your pC02 is in the neighborhood of 40 mmhg. Oxygen Saturation is in the
90-100% range.

Mixed venous blood gases (which are sampled from the pulmonary artery, in
patients with the proper monitoring equipment) on room air tends to be in
the 40-50 mmHg range. This corresponds with about ONE of the FOUR oxygen
molecules on each hemoglobin molecule being extracted, and a saturation in
the 60-75% range. Without a fresh supply of oxygen in the lungs to extract
from, this "desaturated" blood makes a second trip around, and because of
the laws of nature, it is even more difficult for the remaining oxygen to
be extracted. For practical purposes, its essentially NOT going to release
more than two of the four hemoglobin-bound oxygen molecules. Your arterial
oxygen saturation gets too low and you will end up getting confused,
euphoric, or just unconscious.

Hyperventilation in an otherwise healthy individual will not increase the
p02, but can/will drive the pCO2 in arterial blood down to the 20's.
Prolonged hyperventilation will cause vasoconstriction in the brain (as
well as everywhere else), resulting in lightheadedness, dizziness,
cramping in the fingers/toes, and chest pain. I deal with persons on
breathing machines EVERY DAY for a living. If their oxygen level is low,
we dont turn up the rate or volume, we turn up the oxygen concentration.
If their CO2 level is high, THEN we turn up rate/volume to increase the
amount of VENTILATION. Ventilation is the removal of waste products.
Oxygenation is the delivery of oxygen. They are TWO completely different
functions, and not very related to each other, despite the fact they are
happening in the same place at the same time.

It is still possible to pass out from Hypoxia without building up CO2
levels back to the amount needed to trigger the chemoreceptors to tell
your brain "I GOTTA BREATHE". It has been the cause of more than one
drowning/diving accident. If you want further reference on this, a
knowledgeable professional diver, an aerospace medicine MD or a hyperbaric
technician should be able to validate this information.

Dave

Roy Smith writes:

wrote:
This also explains why cabin depressurization above 30000 feet is an
emergency requiring (a) the immediate donning by the pilot(s) of a pressure
mask and (b) emergency descent to an altitude where the conventional
emergency masks used by passengers will be sufficient.

I believe that emergency descent capability is one of the factors that
limits allowable operating ceilings. Some aircraft could get higher than
their certified ceilings, but are not allowed to do so because getting down
to breathable air before the pax suffocated would involve tearing the wings
off (or some other overspeed disaster).

After that golfer bizjet case; I mentally speculated about an
autopilot altitude un-hold. When the cabin pressure failed, the
autopilot would decend to $FEET, that being a level humans would
revive at.

Of course, you COULD run into Mount Whatever, but you're surely
dead at altitude...

It's not clear to me what the survival time is those altitudes; I
thought it was several minutes...


--
A host is a host from coast to
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

"David Lesher" wrote in message
...

It's not clear to me what the survival time is those altitudes; I
thought it was several minutes...

Survival time may be 2-3 minutes, time to totally lose consciousness is more
like 15-30 seconds. The oxygen just 'bleeds' out of your body.

It is still possible to pass out from Hypoxia without building up CO2
levels back to the amount needed to trigger the chemoreceptors to tell
your brain "I GOTTA BREATHE". It has been the cause of more than one
drowning/diving accident.

Some years back I saw a GREAT film on this. They take several guys,
just sitting on a couch, and hook them up to full face masks, bypassing
a CO2 scrubber, and an auxilliary air cannister. So they can just sit
there and breathe normally.

Then they shut off the fresh air, so they are breathing the same air
over and over. After a couple of minutes they start breathing hard,
and finally start grabbing for their masks and gasping for air. The "I
can't stand it any longer and I have to breathe" response.

Then, after they have recovered and are back on the original system,
they shut off the fresh air and ADD the CO2 scrubber. The guys just
sit there on the couch for a few minutes, and slowly, calmly, one by
one, pass out!

jmk

jmk wrote:
It is still possible to pass out from Hypoxia without building up CO2
levels back to the amount needed to trigger the chemoreceptors to tell
your brain "I GOTTA BREATHE". It has been the cause of more than one
drowning/diving accident.


Some years back I saw a GREAT film on this. They take several guys,
just sitting on a couch, and hook them up to full face masks, bypassing
a CO2 scrubber, and an auxilliary air cannister. So they can just sit
there and breathe normally.

Normally, it is the CO2 levels that tell you to breath. How ever those
with chronic obstructive disease (emphasema, long term bronchitis,
etc...) have so much CO2 in their system on a regular basis, that their
body switches to using the O2 levels (hypoxic drive) to control their
breathing. These folks you can put into respiratory arrest giving them
100% oxygen.

After that golfer bizjet case; I mentally speculated about an
autopilot altitude un-hold. When the cabin pressure failed, the
autopilot would decend to $FEET, that being a level humans would
revive at.
I'm sure there are others, but the Citation X will automatically turn
and descend at max speed and level at 14K