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hawk37
8th Aug 2015, 16:08
I was asked if oxygen deprivation due to extremely high altitude (low pressure) would be any different than oxygen deprivation at sea level.

I understand that time of useful consciousness is down to 15 seconds or so at very low pressures, however I'm asking about permanent brain damage.

I came up with the following scenario to illustrate this. Suppose an average individual is subjected to 4 minutes at FL410 in a pressure chamber without any oxygen breathing apparatus. Would he be any more or less brain dead than an individual at sea level who was denied oxygen for 4 minutes (for example underwater with nose/mouth blocked)?

Would one situation be more likely to require the use of CPR or mouth to mouth resuscitation?

I am interested in your thoughts

Hawk

lomapaseo
8th Aug 2015, 16:53
Can we have a specification on the amount of ox at each of these conditions?

percentages and exact time would be a good start.

I realize that at altitude there is still some O2, but what constitutes deprivation below sea level, wet lungs or dry lungs? Are we sleeping or thrashing about?

sonicbum
8th Aug 2015, 16:54
Looks more like a question for Medical and Health section I believe... interesting though.

hawk37
8th Aug 2015, 19:26
Lomapaseo,

consider the lungs start with 5L of air at the respective pressures of sea level and FL 410. 21% which is oxygen. Pressure at Fl 410 is about 2.60 psi, about 17.7% of that at sea level of 14.7 psi. 4 minutes. Dry lungs (consider one cannot inhale anymore). Sitting, not sleeping nor thrashing.

pattern_is_full
9th Aug 2015, 06:27
I would say that yes, the low atmospheric pressure has its own health risks, in addition to how much O2 is actually present. You get fluid in the lungs percolating out of the cells, swelling of the brain, burst blood vessels, etc. that would not occur (or as much) simply due to oxygen deprivation alone.

Pretty much equivalent to the fact that - no matter how much air there is - if you were suddenly exposed to the pressure of 1,000 feet down in the ocean, you would be crushed like a tin can in a vise.

A Squared
11th Aug 2015, 07:45
Not a physiologist, but my WAG is that the guy at high altitudes would be in more serious condition than the guy at sea level, in the same time frame.

All else being equal the guy at sea level will have a greater quantity of air (number of molecules) in his lungs because of the higher pressure, and thus a greater quantity of oxygen in his lungs. And the oxygen which *is* in his lungs will be at a greater partial pressure. If the blood continues to circulate, even though there is no new air being introduced to the lungs, the circulating blood will continue to be oxygenated to some degree to the point that the oxygen in the blood and the oxygen in the lungs reaches a physical equilibrium.

Compare that with someone suddenly subjected to very low atmospheric pressures. At one second before that, the blood is fairly oxygenated at normal pressures. I would speculate that immediately following the pressure drop, oxygen would be flowing out of the blood thru the lungs, so immediately blood oxygen levels would be dropping faster, sooner than the guy at sea level.

So: sea level guy, using up blood oxygen oxygen, but still able to utilize some of the residual oxygen in his lungs.

High altitude guy, blood oxygen being used up *and* being lost thru lungs from the start.

So, high altitude guy reaches whatever level of blood oxygen results in permanent damage sooner.


Not completely sure this is accurate, but that's my speculative opinion based on a little knowledge of chemistry and physics.

edit:

If you think about it, Time of useful consciousness at FL 400 is 15-20 seconds. Pretty much anybody can hold thier breath for 15-20 seconds without passing out. That seems to support my theory on the question.

Avtrician
11th Aug 2015, 09:53
More to the point was how did the person arrive at the altitude situation, and how high is he/she...

At near space, and explosive decompression then good bye..

The decompression chamber example, is at a height above 10000 ft usually. At that situation, there are several minutes before hypoxia sets in. (very similar to intoxication) As the brain runs out of O2, disorientation sets in and eventually collapse. Application of O2 mask results in rapid recovery. I have done this a couple of times in a RAAF Decompression chamber.

In neither situation would Expired Air Resuscitation be of any use as the "Rescuer" would most likely be affected as well.

Being at sea level physically but in the chamber at altitude, is the same as being at the actual height.

john_tullamarine
11th Aug 2015, 12:26
Re chamber runs, many years ago I participated in a 25k rapid decompression session prior to a Mirage ride at ARDU. As discussed above ... but the alarming thing was that I didn't recognise any symptoms myself and duly nodded off into la la land.

We were tasked with the usual pencil and paper exercise (I still have the paper to remind me) and I was so sure at the time that I was doing real fine. Post O2 I was more than surprised to see the gibberish I had been writing.

Needless to say, in later airline flying, I was most attentive to O2 matters ... always.

Peter H
11th Aug 2015, 13:44
individual at sea level who was denied oxygen for 4 minutes (for example underwater with nose/mouth blocked)I don't think that you want to introduce underwater survival times. There is an effect called
the diving response which slows some bodily functions when immersed. Do you want this
added complication?

hawk37
11th Aug 2015, 18:36
I think A Squared has it correct. Much better to be deprived of oxygen at sea level than FL 410, for the time limits and other considerations stated

thanks to all

Hawk

president
15th Aug 2015, 04:53
It seems you all think it's worse at altitude. So please explain why all passengers were technically alive on impact in the Helios crash? They flew for almost 3 hours at FL340. Had they been O2 deprived at sea level they would have been dead in minutes. Any doctors around to comment on this ? Maybe the thing is that at SL when O2 deprived (in water for example) you get nothing once the O2 in your lungs have been used. At altitude you get less than at SL but at least something.

AAIASB final report, section 1.13.1 "Medical Information", p. 57 (PDF page 69 of 198): "The forensic report concluded that the aircraft occupants had heart function during the impact. The report noted that this did not necessarily imply that they were alert. The report further estimated that they were in deep non-reversible coma due to their prolonged exposure (over 2.5 h) to the high hypoxic environment."

archae86
15th Aug 2015, 05:25
They flew for almost 3 hours at FL340. Had they been O2 deprived at sea level they would have been dead in minutes.
I'm not a doctor, nor a pilot, but did take a course in cardiovascular pathophysiology in the Harvard/MIT Health Science and Technology curriculum during my mis-spent years in graduate school at the 'Tute.

So FL340 offers pretty near a fifth of sea level partial pressure of oxygen--which is not much, but a very great deal more than zero. Zero is what you get when drowning or having someone shut off your air intake.

Also relevant is that individual heart muscle cells "want" to beat, and will in fact contract regularly, if still alive in a Petri dish, with no connection either to other cells, let alone a working nervous system. Furthermore, a collection of them will, usually, beat in synchrony, as the fastest will set the time, and the slower ones get reset each time the "wave" hits them.

Lastly, brain tissue "wants" much more nearly fully oxygenation to keep going than does heart, which is able to surge to much higher than resting oxygen consumption to accommodate fight or flight excursions, which are far higher above baseline as a percentage than is the range of brain activity. A resting heart does not need anywhere near full blood oxygenation. To put it another way--as you lower the blood oxygen--the CNS (Central nervous system, including but not limited to the brain) fails long before the heart.

So, I am agreeing with the report you quote--the beating hearts by no mean imply either active, nor yet recoverable, brain function.

Follow the partial pressure of oxygen, and forget this fixation on total pressure--aka altitude.

If a doctor happens along who knows better--please critique.

SloppyJoe
15th Aug 2015, 06:00
A more sensible comparison would be to exhale as much as you can and then try not to breath for a minute, I doubt you would make it. At altitude this is what happens, your lungs may feel full but there is such a low partial pressure in them that no diffusion can take place in the direction that gets the O2 into your bloodstream. Even exhaling all you can here at sea level would still result in some diffusion into your blood, still favourable to suddenly finding yourself at 40,000ft.

Danny42C
15th Aug 2015, 06:47
It might be of some interest to know that the decompression chamber demonstration was in use in the RAF as early as 1942, when I went through my Spitfire OTU at Hawarden. I think it was a mobile unit (similar to the mobile x-ray units which toured the country to detect early tuberculosis).

I think they took us rather rapidly to 20,000 ft (and a Spit I could certainly climb to that in 10 mins) before the "guinea pig" took off his mask. My experience was exactly as described by Avtrician (#7) and john_tullamarine (#8).

It's a long time ago, but what I found most impressive was the insidious onset of the symptons; you have no distress or fear of what you know must be happening to you, you simply slip off into oblivion without a care in the world.
Your "buddy" beside you, on oxygen, watches you like a hawk, and the moment you slump off motionless like a hibernating bear, clamps your mask back on with 100% oxygen.

You "come back" in reverse order to the way you went off. Many people at first refused to accept that they had been "away" at all, even when confronted with the meaningless jumble into which their handwriting had deteriorated.

On a macabre note: I have often thought that this might be an ideal way to commit suicide (if the Law allowed !) or to carry out a death sentence. Cheap, easily available, no pain or fear involved, as easy as falling asleep when dog-tired.

Danny42C.