17. Aeromedical Factors#
17.1. Hypoxia#
- hypoxia
Means “reduced oxygen” or “not enough oxygen.” Most concerning is lack of oxygen to the brain, as it is particularly vulnerable to oxygen deprivation.
There are different forms of hypoxia.
- hypoxic hypoxia
Insufficient oxygen available to the body as a whole (e.g. blocked airway, drowning). At higher elevations, there is less oxygen in the air you breathe (since air density is less, there are fewer molecules per breath). This can cause headaches, drowsiness, impaired decision making, and eventually loss of consciousness.
- hypemic hypoxia
Blood is not able to take up enough oxygen to the cells. Hypemic means “not enough blood.” Might be due to reduced blood volume (severe bleeding, blood donation), or certain blood diseases (like anemia). More often, it is because hemoglobin cannot bind to oxygen—-a symptom of CO poisoning, the most common form of hypoxic hypoxia.
- stagnant hypoxia
Stagmant means “not flowing.” When oxygen-rich blood in the lungs is not moving to the tissues that need it (e.g. when you arm or leg is “going to sleep,” because blood flow has been cut off). Can result from shock, heart issues, or artery constriction. In flight, could be caused by excessive G’s.
- histotoxic hypoxia
Inability of cells to effectively use oxygen. Enough oxygen is going to the cells, but they can’t use it. Can be caused by alcohol and other drugs, such as narcotics and poisons. One ounce of alcohol can equate with up to an additional 2,000 feet of physiological altitude.
17.1.1. Symptoms#
Cyanoasis (blue fingernails and lips)
Headache
Decreased response to stimuli
Increased reaction time
Impaired judgment
Euphoria
Visual impairment
Drowsiness
Lightheaded or dizzy sensations
Tingling in fingers and toes
Numbness
17.1.2. Treatment#
Fly at a lower altitude! Or use supplemental oxygen.
17.2. Hyperventilation#
- hyperventilation
Nerves, panic or anxiety may cause this condition, which is rapid or deep breathing, bringing too much oxygen to the lungs. It leaves you with very low levels of carbon dioxide in your blood, and may cause dizziness or light-headedness, shortness of breath, weakness and confusion.
Hyperventilation can lead to unconciousness.
17.2.1. Symptoms#
The symptoms are very similar to hypoxia, so properly distinguishing between the two is important with regards to treatment.
Visual impairment
Unconscioiusness
Lightheaded or dizzy sensations
Tingling sensation
Hot and cold sensations
Muscle spasms
17.2.2. Treatment#
The goal is to raise the levels of carbon dioxide in your blood. Breathing normally is the best prevention and cure for hyperventilation. Slow your breathing or breathe into and out of a paper bag (less oxygen, more carbon dioxide). Talking aloud also helps overcome hyperventilation.
17.3. Middle ear and sinus problems#
- middle ear & sinus problems
If you are congested, it may cause extreme discomfort at higher altitudes or when descending to your destination, as mucous can block passageways and you may have trouble equalizing air pressure in your middle ear. An unequalized ear can be painful and temporarily reduce hearing sensitivity.
During descents, you might try the scuba diver’s technique for equalizing: pinch the nostrils shut, close your mouth and lips, and blow slowly and gently into your mouth or nose in an attempt to force air through your Eustachian tube and into your middle ear, equalizing the pressure to ambient.
17.4. Spatial disorientation#
- spatial disorientation
Lack of orientation with respect to the position, altitude, or movement of the airplane in space. Vertigo.
When in instrument meterological conditions (IMC), your senses can be fooled and provide false sensations, causing you to be disoriented. Prevention is the best remedy; avoid flying when the horizon is not visible. Train and learn to rely totally on flight instruments.
17.5. Motion sickness#
- motion sickness
Caused by the brain receiving conflicting messages from the body. Usually decreases with exposure and time.
Opening fresh air vents, focusing on objects outside the aircraft, and moving your head smoothly and slowly can help.
17.6. Carbon monoxide poisoning#
- CO poisoning
CO is a colorless and odorless gas produced by all internal combustion engines. It attaches to hemoglobin in the blood 200x as effectively as oxygen, preventing hemoglobin from carrying oxygen to the blood cells and causing hypemic hypoxia. The body requires up to 48 hours to purge itself of CO.
If severe enough, CO can result in death. If a strong smell of exhaust gases is in the plane, you can assume that CO is present and should turn off the heater (an engine leak may be letting exhaust gases into the heat system), open air vents and windows, and use supplemental oxygen if available.
17.7. Stress#
- stress
The body’s response to physical and psychological demands placed upon it. Reaction includes releasing chemical hormones (e.g. adrenaline) into the blood and increasing metabolism to provide more energy to muscles. Stressors may include physical stress (noise/vibrations), psyiological stress (fatigue), and psychological stress (work/personal situations).
There are two categories of stress, acute and chronic.
17.7.1. Acute#
An immediate threat that is perceived as a danger. Triggers a fight or flight response. A healthy individual can usually cope with acute stress and prevent stress overload.
17.7.2. Chronic#
A level of stress that presents an intolerable burden, exceeds and individual’s ability to cope, and causes performance to drop sharply. Unrelenting psychological pressures, such as loneliness, financial worries, relationship or work problems, can produce a cumulative level of stress that exceeds a person’s ability to cope with the situation.
Don’t fly if you’re suffering from chronic stress!
17.8. Fatigue#
- fatigue
Physical fatigue results from sleep loss, exercise, or physical work. Mental fatigue results from stress, prolonged performance of cognitive work, etc.
Fatigue is often associated with pilot error.
17.8.1. Acute#
Short term, a normal occurrence in everyday living. Rest and eight hours of sleep usually solve this. Can be prevented by proper diet, adequate rest and sleep.
17.8.2. Chronic#
Usually has psychological roots, though sometimes is due to an underlying disease. Caused by continuous high levels of stress. Usually requires treatment by a physician.
It can manifest itself as
weakness
tiredness
heart palpitations
breathlessness
heacaches
irritability
When serious enough, it can lead to emotional illness.
17.9. Dehydration and heatstroke#
- dehydration
Critical loss of water from the body.
Caused by:
hot flight decks and flight lines
wind and humidity
diuretic drinks (coffee, tea, alcohol, caffeinated soft drinks)
Common signs:
headache
fatigue
cramps
sleepiness
dizziness
To prevent dehydration, drink two to four quarts of water every 24 hours.
- heatstroke
Caused by any inability of the body to control its temperature.
Keep the flight deck well ventilated and dress accordingly (for example, light-coloured clothing and a hat for protection from the sun in an open canopy cockpit).
17.10. Alcohol#
- alcohol
Alcohol impairs the efficiency of the human body and is closely linked to performance deterioration. Altitude multiplies the effects of alcohol on the brain.
According to 14 CFR Part 91, blood alcohol level must be less than 0.04 percent and at least hours must have elapsed between drinking alcohol and piloting a plane. If blood aclohol is still above 0.04 percent after eight hours, the pilot must wait until it falls below the regulated level. Even if the blood alcohol level drops below 0.04 percent, a pilot must wait at least eight hours after drinking alcohol before piloting a plane.
It is a good idea to be more conservative than the regulations.
17.11. Drugs#
There are no specific references to medication usage in the FAR’s. But there are two regulations to keep in mind from 14 CFR Part 61.53. No person may act as pilot-in-command while that person
Knows or has reason to know of any medical condition that would make that person unable to meet the requirement for the medical certificate necessary for the pilot operation, or
Is taking medication or receiving other treatment for a medical condition that results in the person being unable to meet the requirements for the medical certificate necessary for the pilot operation.
14 CFR Part 91.17 prohibits the use of any drug that affects the person’s faculties in any way contrary to safety.
It is important to consult with an AME the possible side effects of any drugs before flying. Even at general aviation altitudes, changes in concentrations of atmospheric gases may bring on unanticipated side effects.
Any medication that depresses the nervous system, such as sedative, tranquilizer, or antihistamine, can make a pilot more susceptible to hypoxia.
Analgesics reduce pain. Over-the-counter analgesics (e.g. aspirin, acetaminophen, ibuprofen) have few side effects at correct dosages. Prescription analgesics are almost always disqualifying, as they have side effects including mental confusion, dizziness, headaches, nausea, and vision problems.
Anesthetics deaden pain or cause loss of consciousness. They usually wear off within a relatively short period.
Stimulants excite the central nervous system and increase alertness and activity (caffeine, nicotine, etc.). Can produce anxiety and mood swings–dangerous while flying.
Depressants reduce the body’s functioning in many areas. They lower blood pressure, reduce mental processing, and slow motor and reaction responses. Alcohol is a depressant.
While some medications may be safe while flying, the underlying illness it’s treating may itself be disqualifying. For any new medications you take, you should wait at least 48 hours after the first dose to see if there are nay side effects that would affect safety.
17.12. Altitude-induced decompression sickness#
- decompression sickness
Symptoms resulting from exposure to low barometric pressures that cause inert gases like nitrogen, normally dissolved in body fluids, to come out of solution and form bubbles. Most common symptom is joint pain, known as “the bends.”
17.12.1. Treatment#
Put on oxygen mask immediately, switch to 100 percent oxygen
Begin an emergency descent and land ASAP. Seek medical evaluation, even if symptoms disappear.
If one of the symptoms is joint pain, keep the affected area still. Do not try to work the pain out by moving the joint around.
Medical treatment may involve the use of a hyperbaric chamber.
17.12.2. DCS after scuba diving#
Scuba diving allows more nitrogen to dissolve in body tissues due to the increased pressure at depth. A pilot or passenger should let allow the body sufficient time to rid itself of excess nitrogen before flying.
The recommended waiting time before flying above 8,000 feet is:
12+ hours after diving if no controlled ascent was required (non-decompression stop diving)
24+ hours after diving if a controlled ascent was required (decompression stop diving)