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Hypoxia

Hypoxia is a deficiency of oxygen which impairs the brain functions
and other organs. As we gain altitude, the atmosphere decreases in
pressure. Although the air still is 21 percent oxygen, the amount of
oxygen present also is decreased as the air pressure is decreased.

Night vision begins to deteriorate at about 5,000 feet MSL. From about
12,000 to 15,000 feet MSL, judgment, memory, alertness, coordination,
and ability to make calculations are impaired. Some pilots might feel
dizzy or drowsy. A sense of well-being (euphoria) or belligerence can
occur. A pilot's performance can seriously deteriorate within 15
minutes at 15,000 feet MSL. Above 15,000 feet MSL, the periphery of the
visual field grays out to a point where only central vision remains
(tunnel vision). Fingernails and lips turn blue. The ability to take
corrective and protective action is lost in 20 to 30 minutes at 18, 000
feet and 5 to 12 minutes at 20,000 feet MSL, followed soon thereafter
by unconsciousness.

The effect of hypoxia occurs at lower altitudes with the use of some
medication, smoking, alcohol, emotional stress, etc. The worst part is
the fact that hypoxia is very difficult to recognize because of the
gradual dulling of the senses. Since symptoms of hypoxia do not vary in
an individual, the ability to recognize hypoxia can be greatly improved
by experiencing and witnessing the effects of it during an altitude
chamber "flight." The FAA provides this opportunity through
aviation physiology training, which is conducted at the FAA Civil
Aeromedical Institute (CAMI) and at many military facilities across the
United States. To attend the Physiological Training Program at CAMI
telephone (405) 954-6212 or write:

Mike Monroney Aeronautical Center
Airman Education Program Branch
AAM-420 CAMI
P.O. Box 25082
Oklahoma City, OK 73125