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Tamest Fatigue 7 Jan10


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

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Tamest Fatigue 7 Jan10

  1. 1. Fatigue James C. Miller, Ph.D., CPE Miller Ergonomics, San Antonio, Texas Air Force Research Laboratory (retired) [email_address]
  2. 2. Fatigue <ul><li>Context </li></ul><ul><li>Definition </li></ul><ul><li>Simulation </li></ul><ul><li>Detection </li></ul><ul><li>Countermeasures </li></ul>
  3. 3. Context <ul><li>Work of the cognitive performance research group, Air Force Research Laboratory, Brooks City-Base, San Antonio, Texas. </li></ul><ul><ul><li>Dr. Bryce O. Hartman’s group, 1960-2009. </li></ul></ul><ul><li>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. </li></ul><ul><li>Collaborations with other laboratories, especially at Walter Reed (G Belenky, T Balkin et al .). </li></ul>
  4. 4. Context <ul><li>Air Force and other military and non-military, 24/7 operations. </li></ul><ul><li>Highlights of our research-based lectures to physicians (flight surgeons), aerospace physiologists and safety officers (pilots). </li></ul><ul><li>Based upon applied research; our own and that of other laboratories. </li></ul>
  5. 5. Context <ul><li>In any human-machine system, the most variable (unpredictable) component in the system is the human operator . </li></ul><ul><li>Humans provide better pattern recognition capabilities and decision-making skills than can be provided in software. </li></ul>
  6. 6. Context <ul><li>However, humans contribute weaknesses to system reliability. </li></ul><ul><li>These include much more performance variability than one finds in software and modern hardware. </li></ul><ul><ul><li>Especially true for sustained attention and vigilance . </li></ul></ul>
  7. 7. Context <ul><li>Causes of fatigue-related variability : </li></ul><ul><li>Large amplitude, moment-to-moment fluctuations in attentiveness. </li></ul><ul><ul><li>Average performance may be at an acceptable level. </li></ul></ul><ul><li>Brief periods when responses are extraordinarily delayed or absent for a half-second to a minute (&quot;lapses&quot;). </li></ul><ul><li>Microsleeps; i.e. , falling asleep on the job for more than a minute. </li></ul><ul><ul><li>Polysomnography may not resemble nocturnal sleep. </li></ul></ul>
  8. 8. Context <ul><li>After training and currency, the greatest contributor to human variability is cognitive fatigue. </li></ul><ul><li>Fatigue is: </li></ul><ul><ul><li>Ubiquitous (affects all of us), </li></ul></ul><ul><ul><li>Pervasive (affects everything we do) </li></ul></ul><ul><ul><ul><li>and </li></ul></ul></ul><ul><ul><li>Insidious (we are insensitive to its effects). </li></ul></ul>
  9. 9. Context <ul><li>Generally, the primary source of cognitive fatigue is inadequate sleep. </li></ul><ul><li>Many sleep disorders may contribute to this problem. </li></ul><ul><li>However, our main worry is … </li></ul>
  10. 10. Shift Work Sleep Disorder (SWSD) <ul><li>International Classification of Sleep Disorders (ICSD), American Academy of Sleep Medicine (AASM; </li></ul><ul><ul><li>Code 307.45-1, a circadian sleep disorder. </li></ul></ul><ul><ul><li>Essential features: “symptoms of insomnia or excessive sleepiness that occur as transient phenomena in relation to work schedules .” (emphasis added) </li></ul></ul>
  11. 11. Shift Work Sleep Disorder (SWSD) <ul><li>Main problems : </li></ul><ul><li>Inadequate sleep at night, when sleep is most restorative. </li></ul><ul><li>Inability to sleep during the day due to circadian influences. </li></ul><ul><li>Daily amount of sleep is far less than optimal. </li></ul>
  12. 12. Fragility of Sleep
  13. 14. Definitions <ul><li>For practical purposes, we sort the generators of fatigue into six categories: </li></ul><ul><ul><li>Physical </li></ul></ul><ul><ul><li>Circadian* </li></ul></ul><ul><ul><li>Acute* </li></ul></ul><ul><ul><li>Cumulative* </li></ul></ul><ul><ul><li>Chronic </li></ul></ul><ul><ul><li>Task-specific </li></ul></ul><ul><ul><li>*Used in simulations; the focus in this presentation. </li></ul></ul>
  14. 15. Circadian Effects <ul><li>Malaise and fatigue due to: </li></ul><ul><li>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). </li></ul>
  15. 16. Circadian Effects <ul><li>Malaise and fatigue due to: </li></ul><ul><li>Jet lag : A time zone change that is faster than about one time zone per day and exceeds about three time zones. </li></ul><ul><ul><li>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. </li></ul></ul>
  16. 17. Circadian Effects <ul><li>Malaise and fatigue due to: </li></ul><ul><li>Shift lag : A change from day work to night work and vice versa . </li></ul><ul><ul><li>The main external time cue, the daylight-darkness cycle, inhibits re-synchronization. </li></ul></ul><ul><ul><li>For most night workers, re-synchronization never occurs because of not-avoided time cues ( Zeitgebers ). </li></ul></ul>
  17. 18. Acute Fatigue <ul><li>Builds up normally and unavoidably within one waking period. </li></ul><ul><ul><li>Rectilinear decline. </li></ul></ul><ul><li>Recovery from acute fatigue occurs as the result of one good-quality, nocturnal sleep period. </li></ul><ul><ul><li>Asymptotic recovery function. </li></ul></ul><ul><li>The 90% effect in simulation. </li></ul>
  18. 19. Cumulative Fatigue <ul><li>Builds up across major waking and duty periods when there is inadequate recovery (due to inadequate sleep) between the duty periods. </li></ul><ul><li>Recovery from cumulative fatigue cannot be accomplished in only one good-quality, nocturnal sleep period. </li></ul>
  19. 20. The Cure for Fatigue <ul><li>The only known cure for physical fatigue, acute fatigue, cumulative fatigue, jet lag, and shift lag is good-quality nocturnal sleep. </li></ul><ul><li>All other treatments, called fatigue countermeasures (including prescription drugs), are &quot;Band-Aids&quot; that only counter the symptoms of fatigue. </li></ul><ul><li>Eventually, the individual must sleep to recover from all but task-specific fatigue. </li></ul>
  20. 21. Simulation of Fatigue Effects <ul><li>A world-class applied model (or simulation) was developed in 2000-2001, primarily with USAF funding. </li></ul><ul><li>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). </li></ul>
  21. 22. Simulation of Fatigue Effects <ul><li>The three processes in the Sleep, Activity, Fatigue and Task Effectiveness (SAFTE TM ) simulation are: </li></ul><ul><ul><li>Circadian and circasemidian rhythms in metabolic rate and alertness. </li></ul></ul><ul><ul><li>Cognitive performance recovery associated with sleep, and cognitive performance decay associated with wakefulness. </li></ul></ul><ul><ul><li>Cognitive performance effects associated with sleep inertia. </li></ul></ul>
  22. 23. Schematic of Fatigue Model
  23. 24. Validation Example
  24. 25. Simulation in Software <ul><li>The Fatigue Avoidance Scheduling Tool (FAST TM ) is based upon the SAFTE TM simulation. </li></ul><ul><li>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. </li></ul><ul><li>Geophysical model allows jet lag calculations. </li></ul><ul><li>‘ Autosleep’ function fills in best sleep estimate when needed. </li></ul>
  25. 26. 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)
  26. 27. Stupid-Making Schedules <ul><li>“ Stupid-making” work-rest schedules are those that that: </li></ul><ul><ul><li>Ignore the biology of the human component of the human-machine system, and </li></ul></ul><ul><ul><li>Violate the guidance given by Napoleon Bonaparte in 1796 to his commanders: You must not needlessly fatigue the troops. </li></ul></ul>
  27. 28. Stupid-Making Schedules <ul><li>“ Stupid,” American Heritage Dictionary : </li></ul><ul><li>Slow to learn or understand; obtuse. </li></ul><ul><li>Tending to make poor decisions or careless mistakes. </li></ul><ul><li>Marked by a lack of intelligence or care; foolish or careless: a stupid mistake. </li></ul><ul><li>Dazed, stunned, or stupefied. </li></ul><ul><li>“ Stupid,” : </li></ul><ul><li>Lacking ordinary quickness and keenness of mind; dull. </li></ul><ul><li>Characterized by or proceeding from mental dullness; foolish. </li></ul><ul><li>In a state of stupor; stupefied: stupid from fatigue. </li></ul>
  28. 29. Detection of Fatigue Effects <ul><li>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. </li></ul><ul><li>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. </li></ul><ul><li>“ 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.” </li></ul>
  29. 30. Forensic Fatigue Risk Factors <ul><li>For non-military, forensic uses: </li></ul><ul><li>Length of prior wakefulness > 17 hrs </li></ul><ul><li>Amount of prior sleep for the preceding 24 h < 8 hrs </li></ul><ul><li>Time of day 0200h to 0600h (body clock) </li></ul><ul><li>Sleep debt > 10 hrs </li></ul><ul><li>Time zone change - days in zone > 3 </li></ul><ul><li>Source: NTSB Training Center course, Investigating Human Fatigue Factors , Drs. David F. Dinges and Mark R. Rosekind </li></ul>
  30. 31. Forensic Fatigue Risk Factors
  31. 32. Fatigue Countermeasures <ul><li>Sleep hygiene </li></ul><ul><li>Operational Risk Management (ORM) </li></ul><ul><li>Napping on the job </li></ul><ul><li>Tactical caffeine use </li></ul><ul><li>Modafinil </li></ul><ul><li>Dextroamphetamine </li></ul><ul><li>(Mishap investigations) </li></ul><ul><li>(Predictive simulations of schedules) </li></ul>
  32. 33. Sleep Hygiene <ul><li>The most effective countermeasure for fatigue is to do as much as possible to prevent it from occurring in the first place. </li></ul><ul><ul><li>Referring here to sleep debt and cumulative fatigue. </li></ul></ul><ul><li>Use whatever can be done to encourage regular sleep and prevent sleep loss. </li></ul>
  33. 34. Sleep Hygiene <ul><li>Getting enough sleep will reduce the need for other countermeasures. </li></ul><ul><li>Good-quality, nocturnal sleep is a particularly effective control for the three fatigue risk factors: </li></ul><ul><ul><li>Length of prior wakefulness, </li></ul></ul><ul><ul><li>Amount of prior sleep and </li></ul></ul><ul><ul><li>Physical exertion. </li></ul></ul>
  34. 35. Sleep Hygiene <ul><li>How much sleep do we need? </li></ul><ul><ul><li>Eight (8) hours per 24 hours is the average sleep need. </li></ul></ul><ul><ul><li>Half of any given group will need more than 8 hours to prevent cumulative fatigue due to sleep debt. </li></ul></ul><ul><li>Source of sleep hygiene materials: the National Sleep Foundation ( </li></ul>
  35. 36. Operational Risk Management <ul><li>Formal DoD administrative process: </li></ul><ul><ul><li>Identification of hazards </li></ul></ul><ul><ul><li>Assessment of risks </li></ul></ul><ul><ul><li>Analysis of risk control measures </li></ul></ul><ul><ul><li>Possible risk control measures </li></ul></ul><ul><li>Used before USAF missions </li></ul><ul><li>Applied to USAF fatigue risk management by Miller and Eddy (2008) </li></ul>
  36. 37. Napping on the Job <ul><li>Taking a nap can reduce fatigue effects and increase alertness during work and non-work periods. </li></ul><ul><li>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). </li></ul>
  37. 38. Napping on the Job <ul><li>Some other situations where napping would be appropriate are: </li></ul><ul><ul><li>Less than 8 hours sleep during the main sleep period, </li></ul></ul><ul><ul><li>Awake for 30 minutes or longer two or more times during the main sleep period, and </li></ul></ul><ul><ul><li>During a long and/or nighttime work period. </li></ul></ul><ul><li>We preach that “Any sleep is good!” </li></ul>
  38. 39. Napping on the Job <ul><li>Naps should be limited to a time, place and duration that will not interfere with operations. </li></ul><ul><li>It is important to recognize that when naps are needed because of reduced sleep opportunities, personnel are at risk of being critically fatigued. </li></ul><ul><li>Allow 30’ to 60’ for sleep inertia to clear before critical events. </li></ul>
  39. 40. Tactical Caffeine Use
  40. 41. Tactical Caffeine Use <ul><li>When natural fatigue countermeasures (sleep, naps) are impossible, caffeine is a very effective alternative. </li></ul><ul><li>Studies have shown that caffeine significantly improves both alertness (measured by MWTs) and performance (measured by the PVT, etc.). </li></ul>
  41. 42. Tactical Caffeine Use <ul><li>Doses ranging from 200-600 mg are particularly effective in people who do not normally use caffeine. </li></ul><ul><li>However, OTC doses: </li></ul><ul><li>1 cup Maxwell House = 100mg 1 Coke = 50mg </li></ul><ul><li>1 Starbucks Short = 250mg 1 Mountain Dew = 55mg </li></ul><ul><li>1 Starbucks Tall = 375mg 2 Anacin = 65mg </li></ul><ul><li>1 Starbucks Grande = 550mg 2 Excedrin Xtra = 130mg </li></ul><ul><li>1 cup tea = 50mg 1 Max NoDoze = 200mg </li></ul>
  42. 43. Tactical Caffeine Use <ul><li>Caffeine must be used judiciously. Habituation occurs when we take in more than about 250 mg/day! </li></ul><ul><li>The best tactical approach to caffeine use is to take it only right before you need it! </li></ul>
  43. 44. Modafinil <ul><li>Approved by the U.S. Food and Drug Administration (FDA) for the treatment of Shift Work Sleep Disorder. </li></ul><ul><li>Increases the release of monoamines, specifically the catecholamines, from synaptic terminals. </li></ul><ul><li>Also elevates hypothalamic histamine levels, leading some researchers to consider Modafinil a 'wakefulness promoting agent' rather than a classic amphetamine-like stimulant. </li></ul>
  44. 45. Modafinil Caldwell & Caldwell
  45. 46. Dextroamphetamine Caldwell & Caldwell
  46. 47. Fatigue Countermeasures <ul><li>Caldwell JA, Caldwell JL, Schmidt RM. Alertness management strategies for operational contexts. Sleep Med Rev . 2008;12(4):257-273. </li></ul><ul><li>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) </li></ul>
  47. 48. 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
  48. 49. Additional Information <ul><li>Dr. Miller: [email_address] </li></ul><ul><li>Fatigue Reference : </li></ul><ul><li>Shiftwork: An Annotated Bibliography , Naval Postgraduate School, 180 pp., 679 references, draft. </li></ul><ul><li>Fundamentals of Shiftwork Scheduling , AF Research Laboratory, 2006. </li></ul><ul><li>Questions? </li></ul>