Bruce Landsberg (left) and Dave Hirschman don altitude masks at the Nastar training chamber in Philadelphia.
Down for the count
Two felt woozy; one became flush; another had a headache; one got silly; and I passed out.
Six general aviation pilots who live near sea level had strikingly different reactions to hypoxia when exposed to the rarefied air at the AirDocs high-altitude training chamber at Western Michigan University.
My journey to oblivion began when Dr. Gregory Pinnell, a retired U.S. Air Force flight surgeon, asked AOPA colleague Alyssa Miller and I to remove our masks at a simulated altitude of 30,000 feet. Pulse oximeters showed a steady drop in Miller’s oxygen-saturation level from 98 percent at the beginning to 82 percent two minutes later—and then all the way down to an alarming 78 percent.
My own oxygen level started in the 90s and stayed there. After two minutes, I felt a vague but persistent sense that something was not quite right. Then my blood-oxygen level plummeted to 80 percent, and I felt a tingling in my fingers and light ringing in my ears.
We were about to start a simple task—putting nuts and washers on a bolt to test our fine motor skills at altitude—but I thought it wise to take a few breaths of oxygen from my mask first.
I told Pinnell that I was going strap on my oxygen mask momentarily. A few hits of regular air would bring me back to near full strength, but that’s the last thing I recall.
Miller said I became pale and my head fell to my right shoulder while my unseeing eyes stared into the distance. Pinnell sprang into action, first securing my mask tightly around my face and squeezing the air bag to force more air into my lungs. When that didn’t bring me back right away, he swapped masks and put me on a separate system with 100-percent oxygen. Then I’m told I involuntarily straightened out in my seat, and clenched my fists for 30 seconds or so. As the oxygen started to kick in, I did the “funky chicken,” a series of jerky convulsive motions, before my color came back and my eyes finally focused again.
Pinnell was standing in front of me and in his best bedside manner asked, “How do you feel?”
The answer was that I felt terrific. Really. I was rested and refreshed. But I also knew I’d been out for some period of time, and that I’d scared the bejesus out of Pinnell. His pulse oximeter showed his heart was beating a rapid 140 times per minute.
Pinnell had brought the chamber altitude all the way down to 12,000 feet while I “slept,” and I felt a wave of embarrassment and shame. It would take a couple hours to convert the oxygen/nitrogen mix in the chamber to the equivalent of 25,000 feet or more, and a couple of Western Michigan University students who had come for the hypoxia training would have to wait for another day. Sorry!
“You’re what we call a crasher,” Pinnell said. “You do just fine until all of a sudden, you’re not fine.” About one in 100 people he tests is a fellow “crasher.”
The result came as a real surprise because six weeks earlier, I’d been at 24,000 feet in the Nastar altitude chamber in Philadelphia, Pennsylvania, and remained conscious throughout.
There, I had dutifully traced a trail through a simple maze that didn’t seem to require any extraordinary effort. I guided my obedient pencil along the straight and narrow path from start to finish, and it only took a few seconds to complete the task. Even though I felt a bit flush, I believed I had aced the maze test. A pilot’s “time of useful consciousness” is estimated at only three to five minutes at that altitude. My colleague Bruce Landsberg, however, could have used some help. His pencil wasn’t tracking evenly, and he seemed a bit more crotchety than usual.
“Don’t flatter yourself that the heavy breathing you hear has anything to do with you,” Landsberg told Glenn King, our instructor and chief tormentor at Nastar, a private firm that trains pilots, military flight crews, and astronauts to recognize the signs of hypoxia. “And, no, my sarcasm isn’t hypoxia-induced. I come by that naturally.”
My blood-oxygen level had fallen from 100 percent at sea level to 82 percent after three minutes at FL240, but I wasn’t overly concerned. In school, 82 percent is still a B. I did feel a hot spot in the center of my forehead, and I sat particularly still because I sensed the onset of dizziness.
Then, one of the three other pilots going through the training said he was about to faint. The rest of us were told to strap on our oxygen masks, and I felt a wave of relief after just two pressurized breaths.
Studying the pencil marks I had made a few minutes earlier on the maze, I was disappointed to see that they were hopelessly off the mark. It turns out I hadn’t started at the beginning of the maze, and I exited randomly across a solid line. My marks were even worse than Landsberg’s doodles. Any 5-year-old would have had superior cognitive and fine motor skills.
The altitude in the chamber came down to 18,000 feet and we removed our masks again. We sat in darkness for a few minutes and then attempted to read a color chart that looked like it was entirely made from shades of gray. A few breaths of 100-percent oxygen, however, and real vibrant colors seemed to leap off the page. How could I not have recognized them?
The altitude came all the way down to 8,000 feet and I felt completely normal, even without an oxygen mask.
Then the operator demonstrated a rapid decompression, and the altitude shot back up to 24,000 feet with a bang, instant fog, and an involuntary exhalation as the air in our lungs suddenly expanded.
Back in the classroom, King reviewed the results from the four pilots who had been in the chamber.
“Everyone’s response to hypoxia is somewhat different, and pilots should know how to recognize their own individual symptoms,” King said. “A headache, dizziness, or lightheadedness are the most desirable symptoms because they’re easy to recognize and they typically don’t inhibit pilots from taking appropriate action.”
Euphoria, he said, is the worst because it makes pilots feel like everything is just fine, and there’s no compelling reason to make a change.
King said an individual’s hypoxia symptoms can change over time, however, so he recommends revisiting an altitude chamber every four or five years throughout a pilot’s flying career.
The half-day training session at Nastar carries a retail price of $825. The training at Western Michigan University costs $375. Both offer discounts for groups, and the training at both is excellent.
The Nastar facility has the advantage of a “hypobaric” chamber, with powerful pumps that allow it to pressurize and depressurize rapidly, and forced-air oxygen through military-style facemasks with 100-percent oxygen that allow rapid recoveries. The Western Michigan University program uses a “normobaric” chamber that separates nitrogen and oxygen molecules to simulate high-altitude conditions. Its main advantage is that it’s operated by highly experienced flight surgeons with decades of real-world experience.
Landsberg, having returned to sea-level sobriety, said the takeaway for him is obvious.
“Put on the oxygen mask sooner rather than later,” he said. “If there’s ever a question, I’m going to get on oxygen right away. There’s nothing to be gained by delaying this wise course of action—and there may be a lot to lose.”
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