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Tamest Fatigue 7 Jan10
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Tamest Fatigue 7 Jan10



Presented to The Academy of Medicine, Engineering & Science of Texas, 5 Jan 2010.

Presented to The Academy of Medicine, Engineering & Science of Texas, 5 Jan 2010.



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Tamest Fatigue 7 Jan10 Tamest Fatigue 7 Jan10 Presentation Transcript

  • Fatigue James C. Miller, Ph.D., CPE Miller Ergonomics, San Antonio, Texas Air Force Research Laboratory (retired) [email_address]
  • Fatigue
    • Context
    • Definition
    • Simulation
    • Detection
    • Countermeasures
  • Context
    • Work of the cognitive performance research group, Air Force Research Laboratory, Brooks City-Base, San Antonio, Texas.
      • Dr. Bryce O. Hartman’s group, 1960-2009.
    • Principal fatigue scientists in this decade: Drs. John A. Caldwell, J. Lynn Caldwell, Douglas R. Eddy, Steven R. Hursh, James C. Miller, and William F. Storm; many more previously.
    • Collaborations with other laboratories, especially at Walter Reed (G Belenky, T Balkin et al .).
  • Context
    • Air Force and other military and non-military, 24/7 operations.
    • Highlights of our research-based lectures to physicians (flight surgeons), aerospace physiologists and safety officers (pilots).
    • Based upon applied research; our own and that of other laboratories.
  • Context
    • In any human-machine system, the most variable (unpredictable) component in the system is the human operator .
    • Humans provide better pattern recognition capabilities and decision-making skills than can be provided in software.
  • Context
    • However, humans contribute weaknesses to system reliability.
    • These include much more performance variability than one finds in software and modern hardware.
      • Especially true for sustained attention and vigilance .
  • Context
    • Causes of fatigue-related variability :
    • Large amplitude, moment-to-moment fluctuations in attentiveness.
      • Average performance may be at an acceptable level.
    • Brief periods when responses are extraordinarily delayed or absent for a half-second to a minute ("lapses").
    • Microsleeps; i.e. , falling asleep on the job for more than a minute.
      • Polysomnography may not resemble nocturnal sleep.
  • Context
    • After training and currency, the greatest contributor to human variability is cognitive fatigue.
    • Fatigue is:
      • Ubiquitous (affects all of us),
      • Pervasive (affects everything we do)
        • and
      • Insidious (we are insensitive to its effects).
  • Context
    • Generally, the primary source of cognitive fatigue is inadequate sleep.
    • Many sleep disorders may contribute to this problem.
    • However, our main worry is …
  • Shift Work Sleep Disorder (SWSD)
    • International Classification of Sleep Disorders (ICSD), American Academy of Sleep Medicine (AASM; www.aasmnet.org).
      • Code 307.45-1, a circadian sleep disorder.
      • Essential features: “symptoms of insomnia or excessive sleepiness that occur as transient phenomena in relation to work schedules .” (emphasis added)
  • Shift Work Sleep Disorder (SWSD)
    • Main problems :
    • Inadequate sleep at night, when sleep is most restorative.
    • Inability to sleep during the day due to circadian influences.
    • Daily amount of sleep is far less than optimal.
  • Fragility of Sleep
  • Definitions
    • For practical purposes, we sort the generators of fatigue into six categories:
      • Physical
      • Circadian*
      • Acute*
      • Cumulative*
      • Chronic
      • Task-specific
      • *Used in simulations; the focus in this presentation.
  • Circadian Effects
    • Malaise and fatigue due to:
    • Working at night : Errors are much more likely to occur during the midnight-to-dawn period, when sleep drive and sleepiness are highest and body temperature and alertness are lowest (Folkard and Tucker, 2003).
  • Circadian Effects
    • Malaise and fatigue due to:
    • Jet lag : A time zone change that is faster than about one time zone per day and exceeds about three time zones.
      • Re-synchronization of internal circadian rhythms to new external time cues, especially the daylight-darkness cycle, occurs at a rate of 40 minutes to 1 hour per day.
  • Circadian Effects
    • Malaise and fatigue due to:
    • Shift lag : A change from day work to night work and vice versa .
      • The main external time cue, the daylight-darkness cycle, inhibits re-synchronization.
      • For most night workers, re-synchronization never occurs because of not-avoided time cues ( Zeitgebers ).
  • Acute Fatigue
    • Builds up normally and unavoidably within one waking period.
      • Rectilinear decline.
    • Recovery from acute fatigue occurs as the result of one good-quality, nocturnal sleep period.
      • Asymptotic recovery function.
    • The 90% effect in simulation.
  • Cumulative Fatigue
    • Builds up across major waking and duty periods when there is inadequate recovery (due to inadequate sleep) between the duty periods.
    • Recovery from cumulative fatigue cannot be accomplished in only one good-quality, nocturnal sleep period.
  • The Cure for Fatigue
    • The only known cure for physical fatigue, acute fatigue, cumulative fatigue, jet lag, and shift lag is good-quality nocturnal sleep.
    • All other treatments, called fatigue countermeasures (including prescription drugs), are "Band-Aids" that only counter the symptoms of fatigue.
    • Eventually, the individual must sleep to recover from all but task-specific fatigue.
  • Simulation of Fatigue Effects
    • A world-class applied model (or simulation) was developed in 2000-2001, primarily with USAF funding.
    • The Sleep, Activity, Fatigue and Task Effectiveness (SAFTE TM ) model is a 3-process, applied model of human cognitive performance effectiveness (Hursh et al., 2004).
  • Simulation of Fatigue Effects
    • The three processes in the Sleep, Activity, Fatigue and Task Effectiveness (SAFTE TM ) simulation are:
      • Circadian and circasemidian rhythms in metabolic rate and alertness.
      • Cognitive performance recovery associated with sleep, and cognitive performance decay associated with wakefulness.
      • Cognitive performance effects associated with sleep inertia.
  • Schematic of Fatigue Model
  • Validation Example
  • Simulation in Software
    • The Fatigue Avoidance Scheduling Tool (FAST TM ) is based upon the SAFTE TM simulation.
    • FAST TM is a Windows® program by NTI, Inc., under AFRL contract, that estimates the average effects of various work-rest schedules on human cognitive performance by examining work and sleep data entered manually in any of several formats.
    • Geophysical model allows jet lag calculations.
    • ‘ Autosleep’ function fills in best sleep estimate when needed.
  • FAST TM Cognitive performance (%) Cursor for I/O “ Dashboard” Sleep (blue; model input) Work (red; captures data output) Daylight/darkness (gray) Circadian phase (thin red curve)
  • Stupid-Making Schedules
    • “ Stupid-making” work-rest schedules are those that that:
      • Ignore the biology of the human component of the human-machine system, and
      • Violate the guidance given by Napoleon Bonaparte in 1796 to his commanders: You must not needlessly fatigue the troops.
  • Stupid-Making Schedules
    • “ Stupid,” American Heritage Dictionary :
    • Slow to learn or understand; obtuse.
    • Tending to make poor decisions or careless mistakes.
    • Marked by a lack of intelligence or care; foolish or careless: a stupid mistake.
    • Dazed, stunned, or stupefied.
    • “ Stupid,” Dictionary.com :
    • Lacking ordinary quickness and keenness of mind; dull.
    • Characterized by or proceeding from mental dullness; foolish.
    • In a state of stupor; stupefied: stupid from fatigue.
  • Detection of Fatigue Effects
    • During the period 2000-2007, Dr. Miller used FAST™ to assist USAF mishap investigation boards (SIB & AIB) in about nine investigations of Class A and B aviation mishaps.
    • The Naval Safety Center has mandated that all Flight Surgeons use FAST™ in analyzing the 72-hour and 14-day histories in aviation mishap investigations.
    • “ FAST™ has often assisted in identifying fatigue effects that would have been missed otherwise, and occasionally has helped rule out fatigue in cases where it was suspected.”
  • Forensic Fatigue Risk Factors
    • For non-military, forensic uses:
    • Length of prior wakefulness > 17 hrs
    • Amount of prior sleep for the preceding 24 h < 8 hrs
    • Time of day 0200h to 0600h (body clock)
    • Sleep debt > 10 hrs
    • Time zone change - days in zone > 3
    • Source: NTSB Training Center course, Investigating Human Fatigue Factors , Drs. David F. Dinges and Mark R. Rosekind
  • Forensic Fatigue Risk Factors
  • Fatigue Countermeasures
    • Sleep hygiene
    • Operational Risk Management (ORM)
    • Napping on the job
    • Tactical caffeine use
    • Modafinil
    • Dextroamphetamine
    • (Mishap investigations)
    • (Predictive simulations of schedules)
  • Sleep Hygiene
    • The most effective countermeasure for fatigue is to do as much as possible to prevent it from occurring in the first place.
      • Referring here to sleep debt and cumulative fatigue.
    • Use whatever can be done to encourage regular sleep and prevent sleep loss.
  • Sleep Hygiene
    • Getting enough sleep will reduce the need for other countermeasures.
    • Good-quality, nocturnal sleep is a particularly effective control for the three fatigue risk factors:
      • Length of prior wakefulness,
      • Amount of prior sleep and
      • Physical exertion.
  • Sleep Hygiene
    • How much sleep do we need?
      • Eight (8) hours per 24 hours is the average sleep need.
      • Half of any given group will need more than 8 hours to prevent cumulative fatigue due to sleep debt.
    • Source of sleep hygiene materials: the National Sleep Foundation (www.sleepfoundation.org).
  • Operational Risk Management
    • Formal DoD administrative process:
      • Identification of hazards
      • Assessment of risks
      • Analysis of risk control measures
      • Possible risk control measures
    • Used before USAF missions
    • Applied to USAF fatigue risk management by Miller and Eddy (2008)
  • Napping on the Job
    • Taking a nap can reduce fatigue effects and increase alertness during work and non-work periods.
    • A nap can be very effective as a short-term countermeasure against fatigue effects, and to compensate during a period when personnel will need to remain awake for a long time (more than 17 hours).
  • Napping on the Job
    • Some other situations where napping would be appropriate are:
      • Less than 8 hours sleep during the main sleep period,
      • Awake for 30 minutes or longer two or more times during the main sleep period, and
      • During a long and/or nighttime work period.
    • We preach that “Any sleep is good!”
  • Napping on the Job
    • Naps should be limited to a time, place and duration that will not interfere with operations.
    • It is important to recognize that when naps are needed because of reduced sleep opportunities, personnel are at risk of being critically fatigued.
    • Allow 30’ to 60’ for sleep inertia to clear before critical events.
  • Tactical Caffeine Use
  • Tactical Caffeine Use
    • When natural fatigue countermeasures (sleep, naps) are impossible, caffeine is a very effective alternative.
    • Studies have shown that caffeine significantly improves both alertness (measured by MWTs) and performance (measured by the PVT, etc.).
  • Tactical Caffeine Use
    • Doses ranging from 200-600 mg are particularly effective in people who do not normally use caffeine.
    • However, OTC doses:
    • 1 cup Maxwell House = 100mg 1 Coke = 50mg
    • 1 Starbucks Short = 250mg 1 Mountain Dew = 55mg
    • 1 Starbucks Tall = 375mg 2 Anacin = 65mg
    • 1 Starbucks Grande = 550mg 2 Excedrin Xtra = 130mg
    • 1 cup tea = 50mg 1 Max NoDoze = 200mg
  • Tactical Caffeine Use
    • Caffeine must be used judiciously. Habituation occurs when we take in more than about 250 mg/day!
    • The best tactical approach to caffeine use is to take it only right before you need it!
  • Modafinil
    • Approved by the U.S. Food and Drug Administration (FDA) for the treatment of Shift Work Sleep Disorder.
    • Increases the release of monoamines, specifically the catecholamines, from synaptic terminals.
    • Also elevates hypothalamic histamine levels, leading some researchers to consider Modafinil a 'wakefulness promoting agent' rather than a classic amphetamine-like stimulant.
  • Modafinil Caldwell & Caldwell
  • Dextroamphetamine Caldwell & Caldwell
  • Fatigue Countermeasures
    • Caldwell JA, Caldwell JL, Schmidt RM. Alertness management strategies for operational contexts. Sleep Med Rev . 2008;12(4):257-273.
    • Caldwell JA, Mallis MM, Caldwell JL, Paul MA, Miller JC, Neri DF. Fatigue countermeasures in aviation. Aviat Space Environ Med . 2009;80(1):29-59. (AsMA position paper)
  • 30-Hour B-2 Missions “ Our 100 percent success rate of ALLIED FORCE missions is directly attributed to the support of the SUSOPS folks at Brooks.” (specifically, Dr. WF Storm) - LEROY BARNIDGE, JR., Brig Gen, USAF Commander, 509th Bomb Wing
  • Additional Information
    • Dr. Miller: [email_address]
    • Fatigue Reference : www.millergonomics.com
    • Shiftwork: An Annotated Bibliography , Naval Postgraduate School, 180 pp., 679 references, draft.
    • Fundamentals of Shiftwork Scheduling , AF Research Laboratory, 2006.
    • Questions?