What hypoxia sounds like

[Asysin2leads]

The other thread about changes in aircraft flight made me remember this. This is a recording of an ATC conversation and management of a Learjet that lost cabin pressure at a high altitude. Listening to the manner in which the pilots speak and act is a great way to see how a patient that is hypoxia could present. Towards the end they descend to 11,000 feet and the difference in the way they interact is quite striking.

Edited May 4, 2012 by Asysin2leads

[flightmedic608]

Great post Asys, something that we learn in flight physiology. Here is a table of something we learn called time of useful consciousness. Great information. This is without oxygen masks.

Altitude in Flight level Time of Useful Consciousness Altitude in meters Altitude ifeet

FL 150 30 min or more 4,572 m 15,000

FL 180 20 to 30 min 5,486 m 18,000

FL 220 5-10 min 6,705 m 22,000

FL 250 3 to 6 min 7,620 m 25,000

FL 280 2.5 to 3 mins 8,534 m 28,000

FL 300 1 to 3 mins 9,144 m 30,000

FL 350 30 sec tosec 10,668m 35,000

FL 400 15 to 20 sec 12,192m 40,000

FL 430 9 to 15 sec 13,106 m 43,000

FL 500 and above 6 to 9 sec 15,240 m 50,000

Edited May 4, 2012 by flightmedic608

[HellsBells]

Our instructor played this for us in Medic school, its a good one!

[Asysin2leads]

Okay, here's a question I've wondered about. If you can hold your breath for a minute or so, why do you go unconscious in 6 seconds at 50,000 feet? Does the reduced pressure prevent cellular gas exchange or something?

Edited May 5, 2012 by Asysin2leads

[chbare]

You have a large gradient at that altitude. Remember, Oxygen diffuses into our body because the pressure of gas is greater around us and in the alveoli compared to the pressure within our body. This gradient supports the diffusion of Oxygen into our body. At 50,000 MSL, you are essentially in a space equivalent zone and there would exist a large gradient that would cause Oxygen to diffuse in the other direction. Additionally, it would nearly be impossible to hold your breath with any degree of effectiveness due to gas expansion and the large gradient that has already been discussed.

[flightmedic608]

Hi, without going into many aspects of physics...when you fly higher you decrease the total atmospheric pressure which means there are less molecules per breath at that altitude then at sea level. Example Pa at sea level is 765 torr and at 50,000 feet it is 84 torr.

[Asysin2leads]

chbare, I understand what you're saying, but if a person can hold their breath and function for 60 seconds, obviously between what's in your lungs and what's in your blood can sustain you for that long without more air. It's counter-intuitive to me that a person has a minute or so underwater and can function, but a person at 50,000 feet only has six seconds. I am guessing it has to do with the fact that at 50,000 feet whatever gas is left in your lungs exits quickly, so you don't have that reserve for your alveoli to feast on, and in addition, since oxygen exchange at the cellular level depends somewhat on a pressure gradient, oxygen exchange at the cellular level is also impaired. Or is it just that extra gas in your lungs when you hold your breath that makes all the difference?

[chbare]

Underwater, you are under pressure, there exists a pressure gradient to drive Oxygen into the body. At 50,000 MSL, the gradient is reversed. You would literally off gas to the atmosphere. Oxygen would move out of your body following a new gradient. In fact, pressure is so important at altitudes above 50,000, a person would not even survive long wearing an Oxygen mask, they would need to wear a pressurised suit.

[systemet]

Okay, here's a question I've wondered about. If you can hold your breath for a minute or so, why do you go unconscious in 6 seconds at 50,000 feet? Does the reduced pressure prevent cellular gas exchange or something?

This also has to do with the physiology of sudden decompression. There are human populations living at altitudes of ~5,5000- 6,000m, but they've been been born into this environment and adapted to it. Visitors from lower elevations need time to adapt to gradual changes in elevation, otherwise they suffer mountain sickness, abd possibly cerebral or pulmonary edema.

Obviously people have climbed Everest without supplemental O2, but they're very much dying on their way down, and even today the safety margin is very small.

Having to suddenly go from around sea level to high altitude is not something our physiology can handle. I'll try and work out a little more about why.