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  #11  
Old 07-25-2012, 05:56 PM
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grayforge grayforge is offline
 
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I can't imagine the bends being a problem in aviation.

The reason it's an issue in SCUBA diving is that it's easy to go from high pressure to low pressure quickly, causing nitrogen to bubble out of solution in your tissues.

In an RV, even with its respectable climb rate, you don't really get to low pressure very quickly. A military jet, even pressurized, can expose the body to 10,000 feet of altitude change in a matter of a minute or two and I've never heard of bends related issues. Also, pilots aren't always on 100% oxygen. Not sure if it's different now, but in my day, as soon as you were comfortably airborne, the mask was 1/2 unclipped and swinging to the side... until it was time for some hard maneuvering.

Just trying to add some useful info here:
The reason fizz goes away in warm Coke is less that it's diluted by water from the ice, but more that warm water can hold far less CO2 when warm.

Also, exercise isn't synonymous with shaking a can of Coke. It may be that they recommend SCUBA divers not exercise after a long deep dive... possibly because of damage from bubbles going to the wrong places: http://deepstop.wordpress.com/2008/0...-scuba-diving/. Should not be a factor after high altitude flying.

Lastly, be aware of the huge differences in pressure changes between flying and SCUBA diving. With SCUBA, you can get to a pressure 4X Sea Level and go back to 1X in just a minute or two. With Flying, the pressure ratio from Sea Level to FL180 is only .5.

Another way to look at it is:
Sea Level to 120' deep: 15psi --> 75psi or 60psi difference
Sea Level to FL180: 15psi --> 7.5psi or 7.5psi difference
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  #12  
Old 07-25-2012, 06:42 PM
johnny stick johnny stick is offline
 
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Default Bends and flying

Just like Gray forge said,
It will be hard to get the bends while flying. From ground to space, (or back) the maximum pressure change is 1 atmosphere. But when diving, ever 30' of depth is 1 atmosphere. So the problem only comes in if one has been diving and then ascends the extra atmosphere in an airplane. For regular flying, ask any diver how many times he can go from the surface to 30 feet and back; he would probably tell you a lot. In addition, at 18,000 feet, that is 1/2 atmosphere (500 millibars) so it is even more a non issue. JMO, YMMV
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  #13  
Old 07-25-2012, 08:01 PM
cmdro cmdro is offline
 
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The bends in flying might not be as rare as you think. In my 4 years of AF flying I personally know two guys that have had it. One was during my chamber ride at pilot training, don't remember what "altitude" we were at to show the signs of hypoxia but it was only 20-30 something at best. The other was a U-2 pilot I flew with (I know... this one shouldn't really count), but crazy part about his story is he temporarily went blind from it, luckily he regained partial vision before landing.
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  #14  
Old 07-25-2012, 08:54 PM
gciampa gciampa is offline
 
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The instance I was eluding to was a flight of 8 F4-D's flying across the North Atlantic, one of the crew ended up with injuries that required hospitilization.

We were using O2 w/our masks fully engaged, 100% O2 did not alleviate the symptoms.
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  #15  
Old 07-25-2012, 11:39 PM
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Bugsy Bugsy is offline
 
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Default Altitude decompression sickness

Altitude induced decompression sickness is rare, but not non existent. I have treated about 60 cases of altitude induced DCS in my AF career. Most has to do not with how rapid an ascent but rather duration at altitude. What differs alt DCS from diving DCS is the fact that in alt DCS the bubble remained despite the recompression when you decended. The mechanism isnt entirely understood but most believe that at alt there was a local inflamatory response to the bubble and a clot forms or some other effect that hinders the bubble from continueing to pass to the lungs. Doppler of the heart during a decompression from 8,000 to FL250 shows a flood of bubbles passing thru the right side of the heart on the way to the lungs without any symptoms of DCS. symptoms occur when the bubble gets stuck. previous injury, fat, age and dehydration all seem to increase the risk of DCS.

For U2 high flights we use exercide enhanced O2 prebreathing prior to flight. You prebreath 100% oxygen while exerciseing on an eliptical machine to liberate as much of the nitrogen from those stubborn areas as possible. For high altitude airdrops we prebreath 100% oxygen as well.

Why do we recommend no exercise 12 hours post flight of a high altitude exposure. Mechanism not completely understood but believe falls back to that inflamatory response and or an aggregation of a bunch of small bubbles into one larger bubble when you exercise. within 12 hours any bubbles have worked their way thru the system.

Dont mean to hijack a glorious discussion of max performing the RV, but this is probably the right forum to discuss this so anyone contemplatnig pushing the envelope has a fun and safe experience.
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Last edited by Bugsy : 07-25-2012 at 11:42 PM.
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