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.
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.
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.
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.