A mantra in pilot training is that you should train the way you fly, and then fly the way you train. Thanks to its enormous fleet of Level C and D full-flight simulators, FlightSafety International has been providing absolute realism in flight training for many years, except in one area-high altitude physiology. Until now, the only training FlightSafety and other schools could provide is classroom education about the effects of high altitude on the body and pilot performance. Now, for the first time, pilots can safely experience real hypoxia in a flight simulator without leaving the ground.
FlightSafety has teamed up with the Mayo Clinic to create a device that changes the mix of nitrogen and oxygen in the air a pilot breathes to exactly simulate the effects of high altitude physiology. The Mayo Clinic has a long history in the study of flight physiology, dating back to the 1930s. The clinic was among the first medical facilities to use supplemental oxygen to treat patients. That work, plus an intense interest in aviation by its founders, led the clinic to the study of high altitude pilot physiology and development of some of the first effective oxygen masks for pilots. During World War II the clinic built the first centrifuge to study the effects of G-loads on pilots, and that led to the invention of the G-suit that squeezes the lower body, and the straining maneuver that helps pilots combat the debilitating effects of Gs.
The Mayo Clinic also built the first altitude chamber to create a high altitude atmosphere on the surface. Air is pumped out of the chamber to create the thinner, less dense atmosphere of flight. The chamber works well as an altitude simulator, and it has, until now, remained the primary training device for pilots. All military pilots, and many civilians, who have been in the chamber experienced the effects of high altitude without supplemental oxygen, and been better for it.
However, the altitude chamber has several serious drawbacks. Because of the size and weight of a chamber, only a comparative handful have been built. The chamber is totally artificial and absolutely nothing like an airplane, except for maybe the oxygen masks the pilots don after experiencing hypoxia. And there is a small risk of physical harm to people inside the chamber as the pressure changes. Most injuries are relatively minor problems with ears and sinuses, but there is the rare but real possibility of significant damage to the central nervous system.
Way back in 1936 doctors at the Mayo Clinic realized that they didn't need to always use the altitude chamber they had invented to create a realistic altitude simulation for pilots. Instead, by changing the percentage of nitrogen and oxygen in the blend of gases a pilot breathes through a mask, the lungs will behave exactly as they do at high altitude without the risks of big pressure changes on the rest of the body. The clinic called this technology a "mixed-gas paradigm." The U.S. Navy and the Mayo Clinic hold patents on the technology and FlightSafety has worked with both to make the training available to all pilots.
As you may remember from high school biology class, the atmosphere is made up of approximately 21 percent oxygen, 78 percent nitrogen, with the remaining one percent consisting of a bunch of other gases. This ratio of gases remains the same throughout the atmosphere, but the pressure of the combined gases decreases with altitude. It is the change in atmospheric density and pressure, not a decrease in oxygen percentage, that affects people at high altitude. At 18,000 feet the atmosphere is about one half as dense as at the surface. The atmosphere density decreases exponentially above that, along with the pressure of the gases.
Our lungs operate by exchanging oxygen in the air we breathe for exhaust gases through a membrane. The lungs depend on the pressure of the gas in the lungs to push oxygen through the membrane. When the pressure of the air we breath drops, the pressure of the available oxygen molecules also decreases, so the pressure on the part of the intake gas that is oxygen goes down. This so-called partial pressure of oxygen explains why the lungs can't absorb the needed amount of oxygen at high altitude. There simply isn't enough pressure in the available air to push the necessary amount of oxygen across the lung membrane and into the blood stream. When we don an oxygen mask we increase the percentage of oxygen in the gas entering our lungs, and thus the "partial pressure" of the oxygen is similar to that of a lower altitude.
The mixed-gas hypoxia simulator reduces the partial pressure of the oxygen by adding in more harmless nitrogen to the gas delivered to the pilot's mask. Without changing the total pressure of the surrounding atmosphere at the surface, the simulator delivers the same oxygen partial pressure a pilot would experience at high altitude. There is no risk of pressure changes on the rest of the body, but the lungs behave exactly as they would at altitude, and thus the brain doesn't receive enough oxygen and the effects of hypoxia begin.
Many of us have seen films of pilots in altitude chambers flailing about, unable to put on the oxygen mask on command. That's interesting, and perhaps useful as a scare tactic to remind us all that hypoxia can be deadly. But that kind of "training" is useless in the real world because the pilot in the demonstration is unable to save himself, much less his crew and passengers.
FlightSafety, and any sane pilot, have no interest in how a pilot fails when deprived of oxygen to the point of uselessness. We know what happens then. What every pilot needs to know, and what FlightSafety's new training teaches, is how to recognize your own individual early symptoms of hypoxia so that you can take immediate action before the inevitable happens.
The FlightSafety course begins with about two hours of classroom instruction on all aspects of high altitude physiology. Included in the material are the common subjective symptoms of hypoxia, such as euphoria, lightheadedness, dizziness, blurred vision, tunnel vision and so on. Those are some of the symptoms the hypoxia sufferer will experience. The objective symptoms, the ones that can be measured, are poor judgement, mental confusion, cyanosis (turning blue), loss of muscle coordination, euphoria and finally unconsciousness.
