When I was in college at UND, I took a course in aviation physiology as an elective. It was a really good course and we learned all kinds of things about how the body works in a practical and useful manner. Doc Jensen (who still teaches there) oversaw the training and was a wealth of information.
We spent a lot of time talking about hypoxia and I learned that there are several different kinds (four, actually). The one pilots are most familiar with is hypoxic hypoxia - caused by insufficient pressure in the atmosphere. In layman's terms (I know some doctors are reading this and it's probably not as technically accurate as you all could do), this situation is caused by a lack of sufficient pressure to push enough oxygen through the walls of the lungs and into the blood. We can get around it to a point by just making sure that what we're breathing is all oxygen instead of just 21% O2. Remember back to high school science days where we learned that our atmosphere is mostly (~78%) nitrogen?
Anyway, this oxygen deficiency impairs judgment, causes some weird physiological phenomena, and ultimately will cause unconsciousness. We talked about it for a couple of weeks and I found it very fascinating. It is a somewhat intagible subject to discuss, though - this thing about impaired judgment and cognition. Tell me that I won't be able to think all you want, I don't really know what that feels like.
Well, they showed us.
UND is fortunate enough to have a pressure chamber which can hold 10 or so students and a flight surgeon. They put us into that chamber a total of three times so that we could feel the different effects of hypoxic hypoxia. Here's how that went:
We'd pile in and put on our pressurized oxygen masks... we looked like a bunch of novice fighter pilots. Breathing on these things is weird - you have to push the air out and relax to inhale which is kind of the opposite of how you do it normally. I discovered that I was actually unable to talk - I couldn't work my vocal cords while pushing the air out. They tell me you get accustomed to it. I never did. They depressurized the cabin to 25,000 feet as we all breathed 100% oxygen.
We'd get a clip board with some basic math questions (2+2 = ? 3 x 5 = ? 54 - 29 = ?), instructions to write your name 5 times, a very simple maze, etc. Half the chamber's occupants would take their masks off and attempt to do these problems. One of our members was given one of those hollow toys that has many different shapes cut into it and shaped blocks to put through the holes.
As soon as I took my mask off, I felt weird. My fingers were tingly and I had hot and cold splotches on my skin. I felt fine otherwise but that was decidedly not normal. I ignored the feeling and got to work on my questions.
Two minutes in I was struggling to do that last math question. My handwriting was awful. I never even got to the maze. Just a little shy of 5 minutes I started seeing stars around the edge of my vision and the tunnel started to form... and slowly collapse. I took me a few seconds to realize what was happening and I'm not certain that I really knew what was coming anymore, just that I'd had enough. I pushed my mask on and flipped all the switches forward to get some O2. Everything came back at the first breath, along with a headache. I was busy recovering so I didn't notice what all happened to the other crew on my side of the cabin. Once we'd recovered, they had the guys on the other side take their masks off.
That was weird. I knew all these guys pretty well and they were all pretty sharp and healthy. One of them started rubbing his eyes. One got this smirk on his face that escalated to giggles after a couple of minutes. One was working on the toy with the holes and blocks and got them all in after about a minute and a half. They had him open it up, take the blocks out, and try again.
The toy blocks guy was the best. He got 3 of them in and then tried to shove an oval into a square hole. He wasn't a small guy and resorted to brute force since he was so convinced that this peg could get into that hole... and I think he broke the toy. They told us later that this happens usually once a year.
Giggles ultimately just looked around laughing at everybody before settling back for a nap. The doc had to put his mask on for him.
One guy had the "lights are on but nobody's home" look going on. He was the last off oxygen so the doc showed us exactly what was happening. "Hey X, how you doing?" >absent nod< "Would you like to put your oxygen on now?" >absent nod< "You want to go fly a plane?" >absent nod< and so on. I think the doc asked him if he was a hippo or something and got another nod. As soon as the mask was on his face with the O2 flowing, the guy got this shocked look on his face like he'd just woken up. I rather think he did.
If you've never had a chance to get some serious hypoxia awareness training and you fly above 12,000 feet - do it! The experience is well worth it since everybody has slightly different first symptoms. Once you know yours, you'll be much more prepared to deal with it should it start to happen in the airplane.
If you'd be interested in taking a chamber ride, let me know and once we get a large enough group figured out I'll see if I can put together a trip.
EDIT: Dave Bushman found this excellent video taken in the altitude chamber at UND. Excellent visual! http://www.youtube.com/watch?v=cYNQYA6DgBk
Safe flying,
-John Fiscus
Chief Pilot
The Flight Academy
www.theflightacademy.com 
Posted
4 Aug 2009 14:28
by
John Fiscus