Going Up

There is an elevator of sorts inside Building 1045, an unassuming one-story red brick structure on the west side of Andrews Air Force Base outside Washington, D.C. It is the home of the Eighty-ninth Physiological Training Flight, where more than 2,500 military and civilian personnel attend altitude chamber training each year. Here private pilots, flight surgeons, nurses, flight engineers, navigators, air traffic controllers, and reservists get to see how their bodies react to oxygen deprivation.

Hypoxia is an elusive foe. Every person reacts differently to a shortage of oxygen, and I wanted to experience my own symptoms and refresh my memory on the early warning signs as well as the academic subject matter that goes along with it. This kind of training is important because the ability to deal with hypoxia on a more even footing is invaluable. It's so important that the Air Force requires all crewmembers to receive this training every five years. The federal aviation regulations also require ground training in the physiological aspects of high altitude flight for any pilot in command of a pressurized aircraft above 25,000 feet.

Capt. Bruce Christensen, an aerospace physiologist, welcomed a dozen of us as we filed into the classroom at 7:45 a.m. Our group included a corporate pilot, a couple of student pilots, an Air National Guard C-130 loadmaster, and several private pilots. Before we could begin, Christensen checked to be sure there were no medical reasons for us not to participate in the training. Those potential medical problems included having donated blood in the past 72 hours, gone SCUBA diving within the past 24 hours, claustrophobia, ear problems, and having had a cold or dental work within the past seven days.

With the medical issues out of the way, Christensen briefed us on what the day would bring. We would cover flight physiology from the standpoint of the environment, the human body, and the mind. We would become acquainted with several stressors found in the flight environment, not just insufficient oxygen. We were each supplied with a course handout titled Aviation Physiology - an easy-to-read reference outlining the most important factors regarding the physiological effects of flight.

The classroom portion of the training began with an overview of the atmosphere in a sort of mini earth-sci- ence course, and then a fascinating discussion of just how the body's tissues get oxygen through the lungs and the process of respiration. We revisited subjects some of us hadn't considered since high school biology, including alveolar and capillary partial pressures of carbon dioxide and oxygen. Once we all had a basic understanding of how the body gets oxygen, we considered the ways that the body can be deprived of that oxygen.

And as it turns out, there are four types of hypoxia - hypoxic hypoxia, hypemic hypoxia, stagnant hypoxia, and histotoxic hypoxia. Hypoxic hypoxia is what most people think of when they hear the word hypoxia. This condition is the result of inadequate oxygen in the air, usually because of altitude. Hypemic hypoxia is what happens when the blood's oxygen-carrying capacity is compromised as a result of carbon monoxide, blood donations, or anemia. Then there is stagnant hypoxia, related to circulatory impairments, including excessive G forces. Finally, histotoxic hypoxia occurs when something, such as alcohol or narcotics, interferes with the body's ability to use the oxygen available to it.

We learned the objective signs of hypoxia in others, such as increased respiration, cyanosis (turning blue), poor judgment, confusion, and lack of muscle coordination. And then, there were the more subjective symptoms we might encounter ourselves: headache, fatigue, dizziness, tingling, apprehension, or euphoria. (It's worth noting, by the way, that the symptoms of carbon monoxide poisoning are the same as those of hypoxia. The primary difference is that the symptoms of carbon monoxide poisoning fade more slowly than those of hypoxia.)

We reviewed the way the duration of useful consciousness decreases at higher altitudes (reduced by a third to half when a rapid decompression is involved), as well as the ramifications of Boyle's Law relating gas pressures and volume when body cavities are involved (sinus and middle ear problems). The next topic was Henry's Law, which states that the amount of gas in solution varies in direct proportion to the pressure of gas over that solution, which explains the decompression sickness experienced by divers when nitrogen comes out of solution in the bloodstream if they ascend too rapidly. That, Christensen explained, was why we would first undergo 30 minutes of "denitrogenation" by breathing 100 percent oxygen before ascending to our "cruising altitude" of 25,000 feet in- side the chamber.

That led us into the introduction to the oxygen equipment we would be using and a briefing on the flight profile that we would "fly" in the chamber. First, we would ascend to 5,000 feet for an ear and sinus check. Then would come the 30 minutes of breathing pure oxygen. From there we would ascend to 8,000 feet, followed by a rapid ascent - at 3,000 feet per minute - to the equivalent of 25,000 feet. The goal would be for each of us to experience at least three to five of our own symptoms of hypoxia at that altitude before descending to 22,000 feet and then to 18,000 feet for a demonstration of how visual acuity and night vision are affected by lack of oxygen.

Now it was time to experience hypoxia for ourselves. We were each issued our equipment, which we brought with us as we sat in our numbered seats inside the chamber. Two Air Force staff members accompanied us as instructors to explain how our consoles and equipment worked and keep an eye on us. Several other staff members were stationed at observation windows around the chamber to monitor us for signs of hypoxia or problems like hyperventilation or sinus blocks.

The ascent to 5,000 feet went almost unnoticed, except for the altimeter inside the chamber and a tied-off surgical glove, which had previously hung limp from the ceiling and now was slightly inflated. After prebreathing, we went up to 25,000 feet. The air inside the chamber became noticeably foggy at about 8,000 feet, and that glove was now quite large and bloated. Each of us was given a worksheet that included some basic arithmetic problems, a few simple questions, and a list of possible hypoxia symptoms down the right hand side of the page. We were to circle any that we experienced.

Next came the moment of truth, as we were told to remove our oxygen masks (a simple matter of undoing a clasp on one side of our helmets). I started right in on my worksheet as though it were an SAT. OK, eight times nine. It took me no time at all to write in 72. So far, nothing. As I worked the next problem, however, which was to add 32, 58, and 19, I began to realize that I needed to consciously maintain my focus on the columns of numbers, as my attention was wandering. Was 109 the right answer? Who knows? Oh, well. The next problem was to divide six into 7,986. Panic. That's what I was feeling just then. I scanned the list of symptoms. I realized that I was feeling dizzy, so I circled it. I also realized that I was starting to feel another of the symptoms on the list: air hunger - the feeling that I couldn't quite get enough air into my lungs. I looked down the list, and when I saw "trembling" and "tingling," I realized that my fingers were shaking and tingling a bit. I circled those items, too. Trying the division problem again, I saw that there wasn't much space beneath to write, so I just wrote on top of what was printed underneath. I remember considering alternatives of writing smaller or doing some intermediate calculations in my head, but I also remembered realizing that I had just lost about 50 IQ points, and I was getting tired. I circled "fatigue." If "impaired judgment" had been on the list, I would have circled that, too. I didn't see "confusion" on the list, but I certainly was getting there, so I just added it at the bottom (feeling somewhat pleased at my initiative, as I recall). I got to the next problem, multiplying 73 by 48, and I remember the feeling of despair as I tried to remember what eight times seven was. At that point, I gave up on the math and went to some of the questions underneath. "How many minutes have you been off oxygen?" I wrote in "9." (I later learned that we'd been off oxygen about five minutes.) I never even got to the maze underneath, or counting backwards from 100 by fours. At that point, we were told to put our masks back on. That was an instruction we were all happy and ready to follow. As it turned out, five minutes was the limit anyway. The tingling sensation went away, followed about 45 seconds later by the realization that the air hunger and trembling were fading for me, as well. I still felt a bit weak after three minutes back on oxygen.

Next we went down to FL180. They dimmed the lights, and we were each issued a "color wheel" with a color picture of a jet fighter in the center. Off went the oxygen, and in the dim light I saw it only in black and white. But when we went back on oxygen, there was a flood of color, just like in Dorothy's dream in the movie "The Wizard of Oz." It was quite dramatic.

After a lunch break, we returned to the classroom. There we discussed other flight stressors such as fatigue, heat, cold, noise, and carbon monoxide. The next major topic was spatial disorientation. We covered various visual illusions, vestibular illusions, and limitations of vision. We began with some basic eye anatomy, a discussion of vision and various techniques for combating illusions and limitations inherent in instrument flight, and then we went into how the inner ear works in terms of maintaining equilibrium.

The inner ear consists of three small canals, all at about 90 degrees to each other, each filled with a thick fluid and lined with tiny sensitive hairs that relate angular motions and accelerations to the brain. If any constant motion lasts for more than about 25 seconds or acceleration drops below a two-degrees-per-second threshold, however, the movement goes unnoticed, and trouble often follows. In addition, the eyes sweep in a direction opposite to the perceived motion, and angular movement without visual references can induce another phenomenon called nystagmus, where the eyes continue to sweep back and forth like a metronome. It can make the simple act of seeing problematic. Now we would get a chance to test out our inner ears with a ride in the Barany chair, basically a chair that can be spun around to put the inner ear off balance.

With the help of a few brave volunteers, we watched a demonstration of our sensory limitations the using the "yaw" canal, with a subject sitting upright. When the chair stopped spinning, the subject's eyes were going rapidly back and forth - nystagmus in action. The next person to sit in the chair was asked to lean his forehead on the rail that encircles the seat. That brought the "roll" canal into the same plane as the rotating chair. When this volunteer opened his eyes, he found himself lurching sideways as though the whole chair was tipping over - which, of course, it wasn't. I was the third subject. I was instructed to rest the side of my head on the rail, which brought the "pitch" canal into the plane of rotation. Sure enough, when the spinning stopped, I felt as though I were falling forward onto the floor, and my classmates got to see my eyes rolling up and down like the lemons on a slot machine.

For less than the cost of an hour in a Cessna 152 - the fee is currently $35 for this all-day class - you can add a valuable arrow to your quiver of aeronautical experience. Knowing how hypoxia affects you personally can give you extra seconds to react - seconds that could save you from disaster.

You can arrange for the training by contacting the FAA Civil Aeromedical Institute at the Mike Monroney Aeronautical Center, Aeromedical Education Division, AAM-400, Post Office Box 25082, Oklahoma City, Oklahoma 73125; telephone 405/954-4837; fax 405/954-2305. To learn more about how you can invest $35 and a day in your safety, visit the Web site ( www.cami.jccbi.gov/AAM-400/asemphys.html ).