Chapter 3 Fatigue ,Body Rhythms, and Sleep

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Chapter 3Fatigue ,Body Rhythms, and Sleep
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Recognition of the Fatigue Problem

• Fatigue was largely ignored in commercial
  aviation until 1980 when NASA, at the direction
  of the U.S. Congress, initiated a major fatigue
  research program.
• In 1981, based on data obtained form the ASRS,
  NASA reported that fatigue associated performance
  decrements posed a substantial risk to aviation
  safety.
• While the aviation industry has acknowledged the
  existence of long-term and chronic fatigue,
  little has been done in terms of scheduling to
  reduce flight crew exposure to it adverse effects.

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Fatigue

• Fatigue is highly subjective and difficult to
  define.
• Four general interpretations
• Inadequate rest
• Disturbed biological rhythms
• Result of excessive muscular or physical activity
  
• Result of excessive cognitive work

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Factors Contributing to Fatigue

• Body Rhythms
• Noise
• Hypoxia
• Low Humidity Cabin relative humidity (RH) may
  fall as low as 3
• Aggravating and inefficient procedures

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Body Rhythms Chronobiology

• Most biological processes are rhythmic or cyclic
  in character. In other words, they repeat
  themselves at regular intervals.
• Examples of biological cycles
• Sleep
• Hormone secretion
• Digestion
• Pain sensation
• Body temperature
• Menstrual cycle

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Rhythms and Time Cues

• Circadian rhythm 24 Hour Cycle (circa-dies)
• The most common of the rhythms of the body is the
  circadian rhythm.
• 24 Hour rhythm related to the rotation of the
  earth
• Periodicity not quite true closer to 25 hours
• Infradian rhythm Cycle greater than 24 hours.
• Ultradian rhythm Cycle less than 24 hours.

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Zeitgebers

• Entrainment agents which maintain the circadian
  rhythm
• Light and darkness most powerful
• Meals
• Social Activity

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Rhythm of Performance

• Human performance varies during a 24 hour period.
  This performance variation is unrelated to sleep
  deprivation.
• The actual variation in performance at any given
  time is task specific.
• While a natural rhythm, it is influenced by the
  following factors
• Practice
• Heightened motivation
• Increased effort
• Personality differences

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Post Lunch Dip

• Daily period of performance decrement which
  occurs regardless of whether or when lunch is
  taken.
• Critical tasks which require optimal performance
  should be avoided at this time if one has such an
  option.
• Opposite the Circadian Nadir

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Disturbance of Biological Rhythms

• Circadian disrhythmia or desynchronosis
• When the patterns of one's living environment
  change the rhythm of all the cyclic systems in
  the body must readapt to the new environment.

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Resynchronization

• 4 Factors Affecting Resynchronization
• Cycles shift in relation to local time and each
  other.
• Cyclic systems shift their phases at different
  rates.
• Disturbs the body's homeostatic mechanisms.

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Resynchronization

• Resynchronization occurs at different rates
• Phase advance vs. phase delay (eastbound vs.
  westbound)
• Resynchronization does not occur at a constant
  rate
• Exponential function
• Out-of-phase condition halved every 48 hours

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Resynchronization

• Individual differences affecting
  resynchronization rates
• Age
• Introvert vs. extrovert
• Evening person vs. morning person
• Low vs. high neuroticism

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Chronohygiene

• Magic Bullet - chronobiotic drug
• Current chronohygiene practices include
• self-imposed sleep scheduling
• exposure to light/darkness
• meal timing
• exercise
• controlled use of drugs such as caffeine 
• By modifying one's behavior, the affects of sleep
  disturbance and/or deprivation may be minimized.

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Sleep

• Most adults take sleep in one long period each
  day (monophasic) while infants and many animals
  take sleep in several phases during the day
  (polyphasic).
• Once the monophasic pattern has been established
  it becomes a natural rhythm of the brain.
• In cultures where afternoon siestas are the
  custom, the evolution from polyphasic to
  monophasic sleep, which usually occurs before ten
  years of age, is never finally completed.

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Sleep Patterns

• Sleep is generally divided into two types
• Orthodox and Paradoxical (REM)

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Orthodox Sleep

• Sometimes called Non-REM sleep
• Orthodox sleep is divided into four stages
• Stage 1
• Stage 2
• Stage 3
• Stage 4
• Stages 3 and 4 are known as Slow Wave Sleep (SWS)

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Paradoxical Sleep

• Named due to the paradox of an almost waking
  brain wave pattern combined with largely
  paralytic muscles.
• The acronym REM is derived from the initials of
  Rapid Eye Movement, one of the earliest
  characteristics discovered in paradoxical sleep.

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Sleep Cycle
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Naps and Microsleep

• Naps are short sleep periods.
• The restorative effect of a nap varies between
  individuals.
• Research suggests that three factors affect the
  recuperative effect of naps
• Hours of prior wakefulness
• The time of day
• Nap duration most important
• Frequency

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Microsleeps

• Short periods of sleep lasting from a fraction of
  a second up to two or three seconds.
• Individuals experiencing microsleeps are
  generally not aware of them.
• Characteristics of Microsleeps
• Very short in duration (a few seconds or less)
• Occur during periods of low performance
• Occur most frequently during conditions of
  fatigue
• Not helpful in reducing sleepiness

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The Quality of Sleep

• Measurement of the quality of sleep is
  subjective.
• Depth of sleep - Stage 4 sleep is typically
  considered to be deep sleep, yet the sound
  intensity required to arouse a sleeping person is
  not much different in Stage 4 than it is in REM
  sleep.
• Anchor Sleep

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Insomnia

• There are two types of insomnia
• Clinical and Situational

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Clinical Insomnia

• Clinical insomnia Exists when a person has
  difficulty sleeping under normal regular
  conditions and in phase with their body rhythms.
• Clinical insomnia usually takes one of three
  forms
• Inability to get to sleep
• Waking at night and then being unable to return
  to sleep
• Early waking in the morning
• Delayed Sleep Phase Insomnia (DSPI)

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Situational Insomnia

• Situational Insomnia - Difficulty in sleeping in
  a particular situation. e.g. when biological
  rhythms are disturbed.

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Drugs and Sleep

• A variety of drugs may be used to induce sleep or
  counteract the drowsiness and low performance
  associated with sleep deprivation.
• The two common groups of drugs used to induce
  sleep are barbiturates and benzodiazepines.

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Drugs and Sleep

• Barbiturates Not used in aviation
• May be fatal if taken in overdose
• Seriously addictive
• Have adverse performance side effects
• Benzodiazepines Valium, Dalmane, Librium,
  Mogadon
• Non-toxic
• May be addictive
• Unpredictable when combined with alcohol

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Drugs and Sleep

• When taking any such drugs it is important to be
  aware of two characteristics
• Half-life The time it takes for the drug level
  in the blood to fall to half its peak level.
• Wide variations in rates of metabolism from one
  individual to another
• Effect on performance Difficult to measure
  because it is task dependent.

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Non-Prescription Drugs

• Alcohol
• A general, non-selective Central Nervous System
  (CNS) depressant. It is widely used in the
  aviation environment to induce relaxation and
  sleep
• What is certain about alcohol is that although it
  may induce sleep, the sleep pattern is abnormal,
  and REM sleep is suppressed

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Non-Prescription Drugs

• Caffeine
• Increases alertness and normally reduces reaction
  times
• Caffeine disturbs sleep, depending on the amount
  taken and the time interval before sleep

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Sleep Functions and Requirements

• The precise function of sleep and its different
  stages remains largely hypothetical.
• Sleep rebound Following a period of sleep SWS
  deprivation, there will be an excess of SWS in
  the next sleep period. Similar rebounding occurs
  with REM sleep. After total sleep deprivation
  there will be a rebound in SWS and REM but not
  Stage 2.
• The exact nature of physiological restoration
  function is not understood and appears to vary
  greatly among individuals.
• The benefit of sleep on psychological performance
  has been clearly demonstrated.
• Psychological performance deteriorates rapidly
  with sleep loss.
• Changes which take place suggest some impairment
  in the CNS from which it may be deduced that the
  brain requires sleep.

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Sleep and Motivation

• One of the most significant conclusions from
  research is that sleep appears to play a role in
  the maintenance of motivation.
• This loss of motivation can be partly restored by
  extra effort but the individual must be aware of
  the phenomenon to take corrective action.
• This has major safety implications.

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Human Performance and Sleep

• Sleep Deprivation An overall loss of sleep
• Even small periods of sleep deprivation have been
  shown to affect performance. In fact, lapses and
  inconsistency in performance are characteristics
  of a sleep deprived person
• Sleep Disruption Disruption of the normal
  sleeping schedule
• Vigilance and calculation tasks have been shown
  to be significantly impaired and mood adversely
  affect by simply displacing the sleeping period
  by two to four hours

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Effects of Sleep Loss

• Task Dependent
• Complex tasks tend to suffer more than simple
  task
• More interesting tasks suffer less than
  monotonous and dull tasks

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Effects of Sleep Loss

• Vigilance and monitoring tasks are particularly
  vulnerable to sleep loss.
• A person is unlikely to be aware of the manner
  and extent of his deteriorating performance.
• A good comparison is the lack of awareness of
  performance deterioration associated with hypoxia
  and alcohol consumption. Very Dangerous