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Pilot's Handbook of Aeronautical Knowledge
Aeromedical Factors

Health and Physiological Factors Affecting Pilot Performance

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Pilot's Handbook of Aeronautical Knowledge



Table of Contents

Chapter 1, Introduction To Flying
Chapter 2, Aircraft Structure
Chapter 3, Principles of Flight
Chapter 4, Aerodynamics of Flight
Chapter 5, Flight Controls
Chapter 6, Aircraft Systems
Chapter 7, Flight Instruments
Chapter 8, Flight Manuals and Other Documents
Chapter 9, Weight and Balance
Chapter 10, Aircraft Performance
Chapter 11, Weather Theory
Chapter 12, Aviation Weather Services
Chapter 13, Airport Operation
Chapter 14, Airspace
Chapter 15, Navigation
Chapter 16, Aeromedical Factors
Chapter 17, Aeronautical Decision Making




Stagnant Hypoxia
Stagnant means "not flowing," and stagnant hypoxia, or
ischemia, results when the oxygen-rich blood in the lungs
is not moving, for one reason or another, to the tissues that
need it. An arm or leg "going to sleep" because the blood
flow has accidentally been shut off is one form of stagnant
hypoxia. This kind of hypoxia can also result from shock,
the heart failing to pump blood effectively, or a constricted
artery. During flight, stagnant hypoxia can occur with
excessive acceleration of gravity (Gs). Cold temperatures
also can reduce circulation and decrease the blood supplied
to extremities.

Histotoxic Hypoxia
The inability of the cells to effectively use oxygen is defined
as histotoxic hypoxia. "Histo" refers to tissues or cells, and
"toxic" means poisonous. In this case, enough oxygen is
being transported to the cells that need it, but they are unable
to make use of it. This impairment of cellular respiration
can be caused by alcohol and other drugs, such as narcotics
and poisons. Research has shown that drinking one ounce
of alcohol can equate to about an additional 2,000 feet of
physiological altitude.

Symptoms of Hypoxia
High-altitude flying can place a pilot in danger of becoming
hypoxic. Oxygen starvation causes the brain and other vital
organs to become impaired. One noteworthy attribute of
the onset of hypoxia is that the first symptoms are euphoria
and a carefree feeling. With increased oxygen starvation,
the extremities become less responsive and flying becomes
less coordinated. The symptoms of hypoxia vary with the
individual, but common symptoms include:
• Cyanosis (blue fingernails and lips)
• Headache
• Decreased reaction time
• Impaired judgment
• Euphoria
• Visual impairment
• Drowsiness
• Light headed or dizzy sensation
• Tingling in fingers and toes
• Numbness

As hypoxia worsens, the field of vision begins to narrow, and
instrument interpretation can become difficult. Even with all
these symptoms, the effects of hypoxia can cause a pilot to
have a false sense of security and be deceived into believing
everything is normal. The treatment for hypoxia includes
flying at lower altitudes and/or using supplemental oxygen.

All pilots are susceptible to the effects of oxygen starvation,
regardless of physical endurance or acclimatization. When
flying at high altitudes, it is paramount that oxygen be used
to avoid the effects of hypoxia. The term "time of useful
consciousness" describes the maximum time the pilot has
to make rational, life-saving decisions and carry them out at
a given altitude without supplemental oxygen. As altitude
increases above 10,000 feet, the symptoms of hypoxia
increase in severity, and the time of useful consciousness
rapidly decreases. [Figure 16-1]

Time of useful consciousness.
Figure 16-1. Time of useful consciousness.

Since symptoms of hypoxia can be different for each individual,
the ability to recognize hypoxia can be greatly improved by
experiencing and witnessing the effects of it during an altitude
chamber "flight." The Federal Aviation Administration
(FAA) provides this opportunity through aviation physiology
training, which is conducted at the FAA CAMI and at many
military facilities across the United States. For information
about the FAA's one-day physiological training course with
altitude chamber and vertigo demonstrations, visit the FAA
web site: www.faa.gov/pilots/training/airman education/
aerospace physiology/index.cfm.

Hyperventilation is the excessive rate and depth of respiration
leading to abnormal loss of carbon dioxide from the blood.
This condition occurs more often among pilots than is
generally recognized. It seldom incapacitates completely, but
it causes disturbing symptoms that can alarm the uninformed
pilot. In such cases, increased breathing rate and anxiety
further aggravate the problem. Hyperventilation can lead to
unconsciousness due to the respiratory system's overriding
mechanism to regain control of breathing.