A sealed chamber whose ambient pressure and atmospheric composition can be varied to simulate changes in elevation. Hypobaric chambers are used to train pilots, astronauts, and so forth by way of demonstrating the effects of altitude changes on the human body.

Typically, these chambers accomodate 6-12 people, have thick transparent observation windows, and are outfitted with bucket seats with breathing apparati for each occupant. The room is overseen by two external operators, who monitor the chamber's temperature, pressure, and atmospheric gas balance during the training run, as well as the well-being of its occupants. Usually, a certified physician or flight surgeon is present in the chamber to observe the guinea pigs.

I 'flew' in one of these rooms as part of my certification for NASA/Johnson's Vomit Comet program. The experience was incredible, and highly recommended. There are about forty or so seconds of my flight that, although I have them on videotape, are no longer part of my memory. Let me explain.

To begin, the applicants for the test 'flight' were screened for health conditions (such as circulation problems, asthma, or congestion) which would disqualify them. The remainder were fitted for oxygen masks (á lá Top Gun) and headsets, and instructed as to their use. We were seated in the chamber, and instructed to breathe pure oxygen through our masks for 15 minutes to rid our bodies of the pesky nitrogen and other gases which could later lead to evolved gas disorders and other nastiness. We were shown how to operate the mixture controls and key the headset mic. The chamber pressure was then gradually dropped over the course of 20 minutes to mimic the atmospheric pressure present at 25,000 feet.

At this point, we were handed quizes and pencils, and told to start working on them. They contained simple questions, like "23+56+10 = ____". We were then told to remove our oxygen masks and watch each other as hypoxia set in. The results were amazing. People started grinning for no reason, looking around, basically acting drunk. Which, of course, they were, since alcohol also serves to deprive the brain of oxygen.

At about four and a half minutes into the oxygen deprivation, I heard one of the operators chime in (over my headset) "sssshhhhhhclick Seat six has checked out. Sssscchhh". Now, this concerned me slightly, since I was in seat six. The next thing to happen was a bit confusing, and now I know why. For some reason, I next found myself pencilless and with someone helping me get my oxygen mask back on. We descended, did our Valsalva's, and were done. Piece of cake, so I thought. Everything made sense at the time.

After the "Seat six has checked out" comment, the operators decided to play a little trick on me. The flight surgeon came over and said to me, "Touch your nose! There you go, touch your nose!"

My lights were on, but nobody was home. After about 20 seconds of this, I somehow managed to get my finger into the rough vicinity of my nose. When I did, the tape informs me the next thing she tried was "Now, touch my nose!" That was way too much to ask my oxygen-deprived brain. I just sort of stared stupidly at her, blinking. I have no recollection whatsoever of this period of time. Until I saw the tape I would have sworn up and down that, after the "Seat six has checked out" comment, we started descending.

Strangely enough, I got all of my quiz questions right. Of course, I also answered 'yes' to "Do you feel you could safely operate a motor vehicle right now?". That was probably supposed to be 'no'. Seat #5, however, discovered after the flight that she answered the question "Name the last 5 US presidents in backwards chronological order" with 'Clinton, Bush, Ford, Reagan, tummy'. It seems she got a bit mixed up, and also got the munchies during her flight, and thus naturally believed her tummy to have been the right answer to any question.