Aeromedical

Stress

Definition: The nonspecific response of the body to any demand.

Hypoxia

Definition: A condition that results from having an insufficient amount of oxygen in the body.

Types

1. Hypoxic: Occurs when there is not enough oxygen in the air.
   • Causes: High Altitude
2. Hypemic: A reduction in the oxygen carrying capability of the blood.
   • Causes: Blood loss or carbon monoxide
3. Stagnant: Inadequate circulation of the blood
   • Causes: Heart failure or high G maneuvers
4. Histotoxic: Occurs when there is interference with the use of O₂ by body tissue
   • Causes: Alcohol and drugs

Signs and Symptoms

Susceptibility

1. Rapid ascent rates
2. Alcohol: 1 ounce = 2,000 ft PA
3. Individual factors such as metabolic rate and diet
4. Smoking: Loss of 20% night vision, 5,000 PA at sea level
5. Exposure Duration
6. Extremes in temperature (increases oxygen requirement)
7. Self Imposed Stresses
8. Onset time and severity
9. A physically fit person requires less oxygen
10. Physical activity demands more oxygen

Effects of Hypoxia

1. Brain damage to death
2. EPT (Expected Performance Time) is reduced:
   • 18,000 ft = 20-30 min till loss of ability
   • 50,000 ft = 9-12 sec till loss of ability

Stages (I-C-D-C)

1. Indifferent: (Sea level - 10,000 ft) Mild Hypoxia
   • Symptoms: Nigh vision deteriorates at above 4,000 ft
2. Compensatory: (10,000 - 15,000) Pulse Rate, Blood Pressure, Circulation Rate, and Cardiac Output Increases
   • Symptoms: Poor Judgement, Impaired Efficiency, Drowsiness
3. Disturbance: (15,000 - 20,000) Physiological responses can no longer compensate for the oxygen deficiency
   • Symptoms: Vision impaired, impaired flight control, hearing one of the last sense to go, memory, impaired handwriting, happy drunk, mean drunk, coordination, speech
4. Critical: (above 20,000) Happens within 3-5 minutes
   • Symptoms: Loss of Conciseness, Convulsion, and then Death

Prevention of Hypoxia

1. Limit time at altitude
2. Use supplemental oxygen during night flights above 4,000 feet
3. Pressurized cabin

Treatment of Hypoxia

1. Give 100% oxygen if can
2. Descend below 10,000 feet

Self-Imposed Stresses

Definition: Stresses that an aviator has personal control over. Acronym = DEATH

Drugs

1. No self medication unless approved by AME
2. Most drugs have unwanted effects
3. Drugs affect people differently

Exhaustion

1. Lack of rest and sleep
2. Lack of physical exercise

Alcohol

1. Acts as a depressant and adversely affects the body
2. Each ounce consumed increases your physiological altitude by 2,000 feet
3. After drinking alcohol (IAW GOM), you must wait 10 hours and wait until any residual effects are gone before flying

Tobacco

1. Carbon monoxide combines with hemoglobin 200 to 300 times more readily than oxygen. Causes Hypemic Hypoxia
2. Smoking causes reduction in night vision. At sea level, a non-smoker physiological night vision is sea level; however, a smoker’s physiological night vision (at sea level) is 5,000 feet

Hypoglycemia

1. Defined as low blood sugar. With low blood sugar, the body feels weak and fainting occurs.
2. If a meal is skipped, stored sugar in the liver is depleted and a low blood sugar (or hypoglycemia) develops
3. Can avoid by proper nutrition

6 Considerations if using Drugs (SOAPS-C)

1. Self-medication
2. Overdose
3. Allergic Reaction
4. Predictable side effects
5. Synergistic
6. Caffeine

Middle Ear Discomfort

Definition: Discomfort mainly during a descent caused by trapped air expanding or contracting in the middle ear

1. Normally, the air pushing on the outside of the eardrum is equal to the inside pressure within the middle ear. This equalization is maintained by a Eustachian tube from the throat to the middle ear.
2. If the Eustachian tube is clogged (due to a cold usually), the air within the middle ear is trapped and, as you descend, great pressure is exerted upon the eardrum causing pain

Prevention

1. Swallow or yawn
2. Valsalva - close the mouth, pinch the nose shut, and blow sharply (Never Valsalva while Ascending)
3. If not remedied, descend very slowly
4. If not solved on the ground, see doctor.

Spatial Disorientation

Definition: Individual’s inability to determine one’s own position, attitude, and motion relative to a point of reference on the Earth’s surface. The result makes the pilot unable to believe his flight instruments. The pilot mistakenly believes his false senses.

Most Common Terms

1. Sensory Illusion: a false perception of reality. Occurs when the various sensory inputs that affect the brain disagree with each other.
2. Vertigo: dizzy or spinning sensation

Types of Spatial Disorientation

1. Type 1 - Unrecognized (I.e. Heigh-Depth Perception)
   • Most dangerous type
   • The aviator does not think anything is wrong
   • Usually results in a fatal crash
2. Type II - Recognized (I.e. Graveyard Spin)
   • The pilot realizes something is wrong.
   • The pilot does not understand that he is having Spatial Disorientation.
3. Type III - Incapacitating
   • The pilot has an overwhelming sensation of movement and cannot control the aircraft.
   • Usually not fatal if copilot gains control

3 Types of Sensory Systems

1. Visual System
2. Vestibular System
3. Proprioceptive System

Visual System

1. The most important sensory system.
2. The eyes provide 80% of orientation information

Visual Illusions:

1. False Horizon - confusing clouds as the horizon
2. Flicker Vertigo - a flickering light causes sickness. Caused by sun flashing through blades or anti-collision light (at night)
3. Fixation - A visual concentration on one goal
4. Confusion - with ground lights. Aviator mistakes lights on the ground as the horizon
5. Crater - while using NVGs, the IR light creates a visual crater in the ground
6. Relative Motion - mistaking other’s motion for you motion
7. Autokinesis - after staring at a light for 6 to 12 seconds, you wrongly perceive that the light moves
8. Structural - a 2 part windshield can visually split the view of an outside object
9. Heigh Perception - while flying over snow or water there are no visual cues and the pilot has no depth perception. You may feel higher than you actually are.
10. Size Distance - when viewing the lights of a distant aircraft, the aircraft will look farther away when it flies into a haze
11. Altered Planes of Reference - when approaching a mountain range, you feel a need to climb when it is not required
12. Reversible Perspective - at night, an aircraft may appear to be moving away but it is actually approaching

Vestibular System

1. Otoliths Organs: small sensory hairs that respond to gravity and linear acceleration
2. Semicircular Canals: sense changes in angular acceleration. Will react to roll, pitch, or yaw attitude

Vestibular Illusions: 2 Types

1. Somatogyral
2. Somatogravic

Somatogryal Illusions: caused by angular acceleration and deceleration flight

Three Types:

1. Leans
   • Most common form of SD
   • Pilot fails to recognize angular motion during perceived straight and level flight
   • Pilot quickly reacts once roll is noticed and this gives a sensation of rolling the opposite way
   • The attitude indicator shows a level attitude yet the pilot feels as if still rolling
   • This illusion causes the pilot to lean into the direction of the original roll
2. Graveyard Spin
   • Pilot unknowingly enters a descending turn which falsely stimulates the semicircular canals
   • Once recognized, the pilot corrects to straight and level flight, but the pilot will perceive the A/C as turning in the opposite direction
   • The pilot will correct for this false perception and renter the original spin with increased rates of descent
3. Coriolis Illusion
   • Pilot enters a prolonged turn where the stimulated semicircular canal becomes equalized
   • The pilot makes a head motion in a different geometric plane other than that of the turn.
   • The yaw axis semicircular canal is moved to another plane of rotation resulting in a sensation of a turn in the opposite direction and the fluid then stimulates the other two canals
   • The result is a perception of motion in three planes of motion which creates a very strong tumbling sensation

Somatogravic Illusions: caused by changes in linear acceleration and decelerations or gravity that stimulate the otolith organs

Three Types:

1. Oculogravic Illusion
   • When an aircraft accelerates and decelerates, inertia causes the otolith organ to sense a nose high or low condition
   • The pilot falsely corrects this perception by pulling aft (or forward) cyclic
2. The Elevator Illusion
   • Occurs during upward acceleration
   • The eyes will track downward
   • The pilot senses that the aircraft nose is going up
   • The pilot falsely corrects this perception by applying forward cyclic
3. Oculoagravic Illusions
   • Opposite of Elevator Illusion. Occurs during downward movement of aircraft
   • The eyes will track upward
   • The pilot senses that the aircraft nose is going down
   • The pilot falsely corrects this perception by applying aft cyclic
   • May occur when entering autorotation

Proprioceptive System

1. Another name is “seat-of-the-pants” flying
2. This system of orientation is the result of pressure on joints, muscles, and skin
3. An illusion may occur if the pilot feels pressure on his body and misinterprets it for a climb/descent or turn These illusions rarely occur

Prevent Spatial Disorientation

1. Never fly without visual reference points - either the horizon or the altitude indicator
2. Never try to fly VMC and IMC at the same time
3. Trust your instruments
4. Avoid hypoxia, hypoglycemia, anxiety, fatigue, and smoking which all aggravate the illusions

Treatment of Spatial Disorientation

1. Refer to the instruments and develop a good cross-check
2. Delay intuition actions long enough to check both visual references and instruments
3. Transfer flight controls to other pilot if two pilots on the aircraft.

Fatigue

Definition: State of dealing tired, wearing, or sleepy that results from prolonged mental or physical work, extended periods of anxiety, loss of sleep, or exposure to harsh environments. Boring tasks also increase fatigue

3 Types of Fatigue: (ABC)

1. Acute - The type of fatigue experienced between 2 regular sleep periods Characterized by (D-E-N-I-IA-L-L): - Distractibility - Errors in Timing - Neglect of Secondary Tasks - Irritability - Inattention - Loss of accuracy and control - Lack of awareness of errors
2. Chronic - This fatigue occurs over a longer period of time and may be the result of inadequate recovery of successive periods of acute fatigue
   • Much more serious than acute fatigue
   • May be caused by family or financial problems
   • May take weeks to get rid of chronic fatigue
   • Characterized by (W-I-I-P-P-S-L-D):
     1. Weight Loss
     2. Insomnia
     3. Irritability
     4. Poor Judgement
     5. Poor motivations and job performance
     6. Slow reaction time
     7. Loss of appetite
     8. Depressed mood
3. Burnout - (also known as “Motivational Exhaustion”) After prolonged chronic fatigue, the person shuts down and cease functionally occupation and socially. A complete lack of motivation

Prevention

• Total prevention is impossible
• Recommendations
  1. Control sleep environment
  2. Adjust to shift work
  3. Good health and physical fitness
  4. Good eating habits

Treatment

1. Rest and Natural sleep
2. Get up (if awake in bed for > 30 min)
3. Do not sleep too long