Hypoxia: The Enemy Above Continued from page 25 All the organs of our body require oxygen to function properly, but the brain is probably the most finicky con- sumer. Our brain is most happy when it is being well fed with oxygen, and its performance decreases steadily as the supply of available oxygen decreases due to whatever cause—including increases in altitude. The rate at which performance declines, and at what altitude, depends on a number of factors. Humans for the most part do pretty well below 10,000 feet. What shocks many aviators to learn, though, is that symptoms of hypoxia may start as low as 5,000 feet! Everyone’s ability to tolerate hypoxia at altitude can vary dramatically depending on many fac- tors including: • Physical fitness • Recent or chronic illness • Activity level • Fatigue • Alcohol • Smoking How rapidly we climb to altitude and how often our body is exposed to higher altitudes unprotected can affect our body’s ability to acclimate. Persons with medi- cal issues such as asthma, emphysema, and anemia can have significantly less ability to tolerate altitude and hypoxia than fit, healthy individuals. To complicate this tolerance even further, some people are simply better at tolerating altitude than others. As is commonly known in the world of athletics, bodies are not created equal. Just because other aviators—one’s instructor, copilot, or other crew members—are fine at a certain altitude should not lull any pilot into a false sense of security. Although the symptoms of hypoxia can vary from person to person, there are four stages that make up the basis for the FAA’s regulations on flying, which we will review here: • The Indifferent Stage • The Compensatory Stage • The Disturbance Stage • The Critical Stage The first general stage is the Indifferent Stage. This can occur at altitudes as low as 5,000 feet, or even lower. For the most part, this stage primarily affects color and night vision adaptation. Minimal perceptible physical symptoms occur at this height. Unfortunately, because this is the case, the Indifferent stage often goes com- pletely unnoticed. The second stage is the Compensatory Stage. At this stage, the body recognizes something is going on with the available oxygen supply (it’s going down!) and tries to do something about it. Breathing may become quicker and deeper. The heart’s output may increase in an attempt to move more oxygenated blood around the body. Nonetheless, these changes can be subtle and one still may not notice that things are going awry. Stage three is where things get interesting. This may be where the first true hypoxic symptoms become recogniz- able. In this Disturbance Stage, the body cannot com- pensate any longer, and symptoms really begin to show. Finally, in the Critical Stage, the body has lost its ability to defend itself altogether. Unconsciousness will occur here. Self-recovery becomes impossible at this stage. The only hope at this point is to be rescued. Although symptoms will vary from individual to indi- vidual, the hypoxic symptoms any given person experi- ences are usually consistent from one episode to the next. It is for this reason all military aviators have to take a trip to the altitude chamber every five years—to learn, experience, and re-experience their individual hypoxic symptoms in case the need for recognition in the future becomes reality. Can business aviators take advantage of the same opportunity? Should they? YES! In fact, it is easier than ever now that this training can be accom- plished in the “normobaric” environment, without any restrictions on flying or diving afterward. What are the common symptoms of hypoxia? While no one experiences all of these, symptoms can include shortness of breath, rapid heart rate, fatigue, sleepiness, headache, and even euphoria. Concentration can become difficult or even impossible. Judgment and fine motor abilities degrade. 26 Aviation Business Journal | Summer 2020
