AVIATION Oxygen-- page 5 of 6
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The symptoms of hyperventilation and hypoxia are somewhat related and often are misunderstood. The FAA defines hyperventilation as follows: "Hyperventilation, or over breathing, is a disturbance of respiration that may occur in individuals as a result of emotional stress, fright or pain". The respiratory center of the brain reacts to the amount of carbon dioxide found in the blood stream. When you are in a physically relaxed state, the amount of carbon dioxide in your blood stimulates the respiratory center and your breathing rate is stabilized at about 12 to 20 breaths per minute. When physical activity occurs the body cells use more oxygen and more carbon dioxide is produced. Excessive carbon dioxide enters the blood and subsequently the respiratory center responds to this, and breathing increases in depth and rate to remove the over supply of carbon dioxide. Once the excess carbon dioxide is removed, the respiratory center causes the breathing rate to change back to normal.

To check for hypoxia or hyperventilation:

  1. Check your oxygen equipment immediately. See if there is oxygen and the flow is at the proper rate for the altitude you are. The use of Nelson flow meters will verify if your system is working properly.
  2. After three or four deep breaths of oxygen, the symptoms should improve markedly if the condition experienced was hypoxia. (Recovery from hypoxia is extremely rapid).
  3. If the symptoms persist, you should consciously slow your breathing rate until symptoms clear and then resume your normal breathing. You can also breath into a bag, or talk aloud to overcome symptoms of hyperventilation.

Under conditions of emotional stress, fright or pain, the pilot's lung ventilation may increase, although the carbon dioxide output of the body cells remains at a resting level. As a result, he "washes out" carbon dioxide from his blood.

The most common symptoms are dizziness; hot and cold sensations, tingling of the lips and hands, legs, and feet; rapid heart rate; blurring of vision; muscle spasms; sleepiness; and finally unconsciousness.

After becoming unconscious, the breathing rate will be exceedingly low until enough carbon dioxide is produced to stimulate the respiratory center. Hyperventilation occurs as a result of the body's normal compensatory response to hypoxia. However, excessive breathing does little good in overcoming hypoxia.

Several aircraft accidents have been traced to probable hyperventilation. It is recommended that you induce hyperventilation by voluntarily breathing several deeps breaths at an accelerated rate (not while flying). You will begin to get some of the symptoms mentioned. Once you experience several of these symptoms, return to your normal rate of breathing. After you become familiar with the early warnings your body gives you, the likelihood of an accident caused by hyperventilation will be reduced. Caution: Do not hyperventilate while alone or in a standing position. You may fall and injure yourself.

FAA Publications.

Strangely enough, the FAA does not have any publications available that cover the use of oxygen in general aviation. There is an excellent manual that is only given out when you go for an FAA Altitude Chamber ride.

Nitrogen Considerations.

There is a new breathing problem with the advent of the high rate of climb 250+ horsepower homebuilts. Substained rates of climb in excess of 2,000 feet per minute are possible with the Glasair and Lancair type of aircraft. Total time to climb to 20,000 feet can be less than 10 minutes. Problem here is that the average person's body cannot adapt to that change of altitude in that time period. I understand that it takes at least 20 minutes for the body to adjust to that change. The problem is nitrogen gas bubbles in the body. This is called "the Bends", the same problem that can occur in deep sea diving. Extreme pain can occur and if a nitrogen gas bubble occurs in the brain, death can occur. Climbing to 25,000 feet makes the possibility of the bends even more so. Some people may make it to 20,000 feet OK, but a even greater number of people may not make it to 25,000 feet in these short time periods.

To make things worse, there are no FAA requirements or recommendations about the effects of high rates of climb. Hopefully the FAA will and the manufactures of these aircraft will advise pilots about these problems. There are two ways of solving the problem for most situations. One is to limit the climb to 20,000 feet to less than 1,000 feet per minute. The other suggestion is to put on the oxygen soon as you start the engine and let your body start adapting sooner.

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Updated: 2/9/98