Human Factors in Aviation
Emotion & Physiological Factors
Introduction
I. Descartes Mind/Body dualism
A. Traditional view of separation between psychological and physiological leads people to allocate relatively less weight to physiological influences on psychological processes.
II. Developmental Neurophysiology
A. Brain develops with body
B. Intricate interconnections between “motor”, “perceptual”, “cognitive”, and “affective” structures.
C. Better to view mind/brain/body as integrated system
1. “Think with the body”
D. Brain
1. Monitors internal and external environment
2. Uses affective information to:
i. Judge importance,
ii. Allocate attention,
iii. Allocate resources
3. Important thoughts linked to actions and preparations for action – allows for fast response to threats
E. Built for limited range of environmental conditions
1. Can adapt slowly to wide shifts on conditions
2. In short run, when outside environment, operation is suboptimal
i. Insufficient oxygen (hypoxia)
ii. Too cold (hypothermia) or too hot (hyperthermia)
iii. Insufficient food (hypoglycemia)
iv. Insufficient rest (fatigue)
v. Circadian desynchronization
vi. Stress
III. Practical Aviation Summary
A. Pilots should carry (and use):
1. water bottles to stay hydrated
2. energy bars to avoid hypoglycemia
3. supplemental oxygen to avoid hypoxia
B. All aviation professionals should be scheduled to avoid
1. Waking periods (including travel, meal, planning times) longer than 19 (preferably 16) hours
2. Interference with circadian rhythms (e.g., no “double-backs”)
C. To avoid deleterious effects of stress:
1. Procedures should be designed to allow for expected deterioration under stress
2. Individuals should be trained in stress management techniques
Hypoglycemia
14. Physiology:
a. Brain is extremely active organ but has no glucose stores; requires continual transport of glucose through blood stream.
b. Hypoglycemic when blood Glucose Levels (BGL) below normal
15. Effects
a. Cognition
i. Decreased performance on tasks requiring:
1. attentional focus
2. effortful control
3. short term memory
4. visual detection tasks
ii. Higher cognitive functions show decrease before lower
b. Affect
i. Headaches
ii. Hunger
iii. Feeling “sluggish”
iv. Feeling drowsy
c. Manifest Performance
i. 20-22% runway incursion incidents attributable in part to lack of food for 12-20 hours prior to incident (FAA Pilot Surface Incident Safety Study 1993)
ii. Barshi & Mauro Food Log Study
1. Subjects: 88 airline pilots flying 4 day trips
2. Method: Kept diary of symptoms, food intake
3. Results:
a. Pilots eat less when on trips
b. At this airline, tend to have morning and afternoon shifts
c. Morning shift much less likely to have eaten a meal in previous 8 hours
d. Don’t eat in cockpit
e. Pilots not eating within 8 hours demonstrated 22% increase in reported symptoms of cognitive dysfunction.
16. Remediation
a. Design
i. Schedule to allow regular meals
ii. Provide nutritional food
iii. Provide energy bar snacks
b. Train
i. Eat regular meals
ii. Avoid apparent “quick fix” options
iii. Carry (and use) energy bar snacks in flight bag
iv. Recognize symptoms and act immediately
1. Because higher cognitive functions are first to show deterioration, performance probably will be degraded before
c. Select
i. Individual differences in BGL range
ii. Individual differences in susceptibility
Hypoxia
I. Physiology
A) Air is mostly N2 (79%), O2 (21%)
1) Small proportion of other gases including CO2
B) Respiration
1) Intake O2
2) Remove CO2
3) Controlled largely by presence of CO2; lack of O2 is a relatively ineffective control on respiration
4) Passive process depends on partial pressure of gases
(a) Partial pressure depends on air pressure and proportion of gas in air
(b) Air pressure decreases with altitude
C) Types of hypoxia
1) Hypoxic hypoxia results from an inadequate oxygenation of the arterial blood and is caused by reduced oxygen partial pressure.
2) Anemic hypoxia results from the reduced oxygen-carrying capacity of the blood, which may be due to blood loss, anemia, carbon monoxide poisoning, or by drugs.
3) Stagnant hypoxia is caused by a circulatory malfunction which results, for example, from the venous pooling encountered during acceleration maneuvers.
D) Effects on vision
1) Eye uses large quantities of O2 through direct and cardiovascular transmission
2) Difficulty in dark adaptation and decreased nighttime visual acuity are first effects of hypoxia.
II. Effects
A) Stages
B) Indifferent Stage.
1) There is no observed impairment.
2) The only adverse effect is on dark-adaptation, emphasizing the need for oxygen use from the ground up during night flights.
C) Compensatory Stage.
1) The physiological adjustments which occur in the respiratory and circulatory systems are adequate to provide defense against the effects of hypoxia.
2) Factors such as environmental stress or prolonged exercise can produce certain decompensations.
3) In general, in this stage there is an increase in pulse rate, respiratory minute volume, systolic blood pressure, and cardiac output.
4) There is also an increase in fatigue, irritability, and headache, and a decrease in judgment. The individual has difficulty with simple tests requiring mental alertness or moderate muscular coordination.
D) 3. Disturbance Stage. I
1) n this stage, physiologic responses are inadequate to compensate for the oxygen deficiency, and hypoxia is evident.
2) Subjective symptoms may include headache, fatigue, lassitude, somnolence, dizziness, "air-hunger," and euphoria.
3) At 20,000 feet, the period of useful consciousness is 15 to 20 minutes. In some cases, there are no subjective symptoms noticeable up to the time of unconsciousness.
4) Objective symptoms include:
(a) Special Senses. Peripheral and central vision are impaired and visual acuity is diminished. There is weakness and incoordination of the extraocular muscles and reduced range of accommodation. Touch and pain sense are lost. Hearing is one of the last senses to be affected.
(b) Mental Processes. The most striking symptoms of oxygen deprivation at these altitudes are classed as psychological. These are the ones which make the problem of corrective action so difficult. Intellectual impairment occurs early, and the pilot has difficulty recognizing an emergency situation unless he is widely experienced with hypoxia and has been very highly trained. Thinking is slow; memory is faulty; and judgment is poor.
(c) Personality Traits. In this state of mental disturbance, there may be a release of basic personality traits and emotions. Euphoria, elation, moroseness, pugnaciousness, and gross overconfidence may be manifest. The behavior may appear very similar to that noted in alcoholic intoxication.
(d) Psychomotor Functions. Muscular coordination is reduced and the performance of fine or delicate muscular movements may be impossible. As a result, there is poor handwriting, stammering, and poor coordination in flying. Hyperventilation is noted and cyanosis occurs, most noticeable in the nail beds and lips.
E) Critical Stage. In this stage of acute hypoxia, there is almost complete mental and physical incapacitation, resulting in rapid loss of consciousness, convulsions, and finally in failure of respiration and death
III. Remediation
A) Increase partial pressure of O2
1) Use supplemental O2
2) Pressurize cabin
3) Positive pressure breathing apparatus
B) Altitudes
1) Effects noticeable above 5,000 feet
2) Effects substantial above 10,000 feet
3) FAA requirement for extended flight above 12,500 feet
C) Training, Selection
1) Individual differences in susceptibility
2) Extended exposure leads to adaptation
Stress
I. Definition
A. Poorly defined term
1. Environmental condition
2. Affective state
3. Physiological response
B. Selye “Generalized Activation Syndrome”
1. Physiological consequences
2. Psychological consequences
C. Limited evidence for unitary arousal process
1. Evidence of physiological differentiation
D. Lazarus “Coping Response”
1. Primary appraisal
2. Secondary appraisal
II. General model of emotional response to stressors
A. Cognitive theory of emotion
B. Effect of environmental factors on individual depends on appraisal of situation and resources
C. Emotional States
1. Fear
i. Difficulty shifting attention
ii. Motivation increase leading to enhanced effort
iii. Apparent short term memory capacity limitation
iv. Mauro & Barshi studies
v. Short term memory occupied by worry
vi. Behavioral tendency to escape
2. Anger
i. Behavioral stereotypy
ii. Short term memory occupied by intrusive thoughts
iii. Behavioral tendency to attack
iv. Mauro & Barshi studies
3. Joy
i. Open minded
ii. Limited desire to exert effort
iii. Behavioral tendency to maintain state
D. Boredom
1. May be high arousal – lead to effort to escape
2. May be low arousal – similar to depression
E. Sadness
1. Lack of motivation leading to decreased effort
2. May lead to more realistic perceptions of risk
III. Remediation
A. Redesign task to avoid stressors
B. Redesign task to avoid problems caused by stress
C. Habituate to stressors
D. Cognitive restructuring of primary appraisal
E. Cognitive restructuring of secondary appraisal
Fatigue
I. Categories
A. ACUTE FATIGUE
1. Produced by physical exertion or sleep loss
2. Alleviated by a single rest period
B. CHRONIC FATIGUE
1. Medical or psychological problem
2. Chronic Fatigue Syndrome
C. OPERATIONAL FATIGUE
1. Often caused by sleep loss and circadian desynchronization
2. Often caused by continuous or sustained operations
3. Most commonly seen after 3-4 days of heavy tasking
4. Not relieved by a single sleep period
II. Effects
A. Cognition
1. Likely to demonstrate effects before self-aware
2. Decreased attention focusing
i. Increased detection errors
3. Decreased attention shifting
i. Reduced scan rates
ii. Increased fixation
iii. Decreased situational awareness
4. Decreased effort
i. Less likely to perform low-demand tasks
ii. Decreased recall
5. Slower response time
i. Timing errors in response sequences
ii. Greater control lag
6. Increased tendency to fall asleep
7. Poor judgment
8. Spatial disorientation
B. Affect
1. Irritability
i. Less likely to converse
III. Exacerbated by
A. Drugs
1. Barbiturates
2. Benzodiazepines
3. Aspirin
4. Antihistamines
5. Alcohol
B. Non-Pharmacological interventions
1. Vigorous exercise
2. Warm baths
3. Tryptophan (milk, cheese, turkey, etc.)
IV. Remediation
A. Design
1. Avoid schedules that require 12 hours or more of continual work-related activities
2. Avoid schedules that do not allow 5-8 hours of sleep per day
B. Train
1. Recognize symptoms and act to address cause
i. Sleep
ii. Naps
2. Take actions to ameliorate effects
i. Drugs
a. Caffeine
b. Methamphetamine
c. Amphetamine
d. Methylphenidate
3. Alter Tasks
i. Increase use of performance aids (e.g., checklists)
ii. Increase use of human resources (e.g., crew, ATC)
C. Select
1. Individual differences in susceptibility
2. Changes with age,
3. Interacts with other health factors
Circadian Desynchronization
I. Circadian Rhythms
A. We have intrinsic biological clocks with a cycle of roughly 24-25 hours. Many bodily functions cycle about these daily circadian rhythms; e.g.:
1. Blood Pressure
2. Heart Rate
3. Core Body Temperature
B. Performance also cycles about normal circadian rhythms.
1. Given the typical circadian cycle, performance peaks between 1200 and 2100 and falls to a minimum circadian trough between 0300 and 0600.
C. While the body clock is inherently capable of monitoring the passage of time, it differs from most clocks in that its period is flexible and must be set, or synchronized, before it can accurately predict the timing of periodic environmental events. Entrainment is accomplished by external synchronizers:
1. Sunrise-Sunset
2. Ambient Temperature
3. Meals
4. Social Cues
II. Circadian Desynchronization
A. Modern Problem caused by east/west travel faster than biological clock can resynchronize.
1. Eastward travel shortens the day.
2. Westward travel lengthens the day
3. Resynchronization occurs much more rapidly when traveling west
4. Resynchronization of functions may occur at different rates
B. Effects
1. Cognitve
i. Deficits in performance
a. Slow reaction times
b. Defective memory for recent events
c. Errors in computations
ii. Decreased motivation
a. Tendency to accept lower standards of performance.
2. Affect
i. Anxiety
ii. Irritability
iii. Depression
3. Sleep disturbances
i. Can cause fatigue
III. Remediation
A. Design
1. Avoid schedules that require work during offset periods after circadian desynchronization
B. Prior adjustment
1. Biological clocks sensitive to light/dark cycles; can be artificially adjusted with proper lighting near correct diurnal cycles
C. Sleep
1. Sleep cycle closely tied to temperature cycles
2. People sleep longer and feel better when they go to sleep near temperature trough.
3. Two times when body is prepared to sleep:
4. Between 2200-0600
5. Post-prandial dip
6. Sleep requirements vary dramatically among individuals.
7. A minimum of 5 hours of uninterrupted sleep during the circadian trough is necessary to maintain performance in the lab.
8. Sleeping in excess of 10 hours may produce “sleep drunkenness”.
9. When environmental factors and physical and mental workload exceed normal limits, the minimum amount of sleep needed to sustain performance is greater
D. Napping
1. When sleep is not available or shortened by operational concerns, short naps may help.
2. Even naps as short as 10 min are restorative in nature
3. Long naps (typically greater than 1 h) may cause “sleep inertia”
4. Sleep inertia may last 5-20 min upon awakening
5. Practice can lead to faster napping
E. Drugs
1. Melatonin
2. Mepiprazole hydrochloride
3. Theophylline
4. Pentobarbitone
F. Select
1. Individual differences in susceptibility
Sleep Cycle
Hypoglycemia
Percentage of Flights on Which Symptoms Were Experienced by Reporting Time
No Symptom / Symptom / Total / NReport <0945 / 59.8 / 40.2 / 100.000 / 502
Report >0945 / 67.1 / 32.9 / 100.000 / 498
Total / 63.4 / 36.6 / 100.000
N / 634 / 366 / 1000
X2(1)=5.75, p=.016
Most Recent Food Intake by Reporting Time: Percent of Duty Cycles
Most Recent Food IntakeReporting Time / <= 8 hours / > 8 hours / Total / N
< 0945 / 37.149 / 62.851 / 100.000 / 498
> 0945 / 90.361 / 9.639 / 100.000 / 498
Total / 63.755 / 36.245 / 100.000
N / 635 / 361 / 996
X2(1)=305.12, p<.001)
Table 1-7 Stages of HypoxiaStage / Altitude in feet / Arterial oxygen saturation (percent)
Breathing air / Breathing 100 percent O2
Indifferent / 0-10,000 / 33,000-39,000 / 95-90
Compensatory / 10,000-15,000 / 39,000-42,000 / 90-80
Disturbance / 15,000-20,000 / 42,200-45,200 / 80-70
Critical / 20,000-23,000 / 45,200-46,800 / 70-60
Table 1-8 Time of Useful Consciousness
Altitude (1,000 feet) / Rapid disconnect (moderate activity) / Rapid disconnect (sitting quietly)
22 / 5 minutes / 10 minutes
25 / 2 minutes / 3 minutes
28 / 1 minute / 1 minute 30 seconds