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Raghu Upender, MDAssistant Professor in Neurology Medical DirectorVanderbilt Sleep Disorders Center
Fatigue Science & SafetyOccupational Sleep Medicine
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• None
DISCLOSURES
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EXXON VALDEZ
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DRIVINGWHEN
DROWSY
• 71,000 non-fatal injuries occur per year
• 1,550 fatal injures occur per year
• $12.5 billion in monetary losses
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How can we mitigate the risk of human error in
future disasters?
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• Define fatigue and sleep
• Review effects of Sleep loss
• Review sleep physiology
• Describe fatigue modeling
• Fatigue risk management
OUTLINE
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Physical or mental “exhaustion arising from labor, exertion, or stress”
-Merriam-Webster Dictionary
FATIGUE DEFINITION
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FATIGUE SEVERITY SCALE
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Fatigue ≈ performance degradation
FATIGUE IN THE WORK PLACE
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• PVT is relatively brief, easy to administer, and can be repeated multiple times through the day.
• The PVT measures simple reaction time to a visual stimulus
• PVT reaction times correlate well with other cognitive tests.
PSYCHOMOTOR VIGILANCE TEST
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Doran SM, Van Dongen HPA, Dinges DF. Arch Ital Biol 2001;139:253-267.
PVT REACTION TIMES
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Saper CB et al. Nature 437, 1257-1263 (27 October 2005)
ASCENDING AROUSAL SYSTEM
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Saper CB et al. Nature 437, 1257-1263 (27 October 2005)
SLEEP PROMOTING VLPO
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Saper CB et al. Nature 437, 1257-1263 (27 October 2005)
FLIP FLOP SWITCH
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• NarcolepsySleepiness intrudes into wakefulness due to
• Loss of orexin producing neurons leads to loss of orexin’s stabilizing effect on arousal
• Insomnia in the elderlyWakefulness intrudes into sleep due to
• age related loss of VLPO neurons leads to less effective suppression of arousal system.
CLINICAL EXAMPLES
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• During prolonged arousal –Arousal system weakens due to
exhaustion–Sleep pressure accumulates–Wake promoting circuits are overwhelmed
and abrupt transition to sleep occurs causing momentary lapse
FLIP-FLOP SWITCH AND FATIGUE
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Wesensten NJ, Thorne DR, et. Al. Aviat Space Environ med 2004;75:520-525
PVT SPEED AND SLEEP DEPRIVATION
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• Process S
• Process C
SLEEP – WAKE REGULATION
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–Sleep homeostatic drive
– Increases during the wake period
–Declines during sleep
–Quantified by slow wave sleep
PROCESS S
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Taber KH et al. The Journal of Neuropsychiatry and Clinical Neurosciences 2006
CEREBRAL BLOOD FLOW ACROSS SLEEP STATES
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PERFORMANCE RESERVOIR
http://dnr.wi.gov/org/water/wm/dsfm/dams/gallery.html
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• Master Circadian oscillator
• Provides alerting signal
PROCESS C
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Richardson GS: The human circadian system in normal and disordered sleep. The Journal of Clinical Psychiatry 2005; 66(Suppl 9):3—9.
THE TWO-PROCESS MODEL OF SLEEP REGULATION
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PROCESS WPROCESS OF AWAKENING
Balkin, TJ et al. Brain 2002;125:2308-2319
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• Human error due to fatigue is fundamentally stochastic, i.e. random.
• Performance lapses that occur due to wake state instability are also stochastic.
• Though the individual performance lapses in
attention occur randomly, the probability at which they occur is predictable.
BASIS FOR FATIGUE MODELING
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FATIGUE MODEL
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Belenky, G et. al. J Sleep Res. 2003 Mar;12(1):1-12.
PVT SPEED AND SLEEP TIME
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Hursh SR. Aviat Space Environ Med 2004; 75:A44-53
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FATIGUE VS. ACCIDENT RISK
Hursh SR et al. SAE Trans 2004;113:111-119.
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“I’m too tired to listen to a story right now, mom. Just e-mail something and I will read it tomorrow.”
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• Approximately 21% of adults average ≤ 6 hours of sleep
• 70 million American experience chronic sleep loss on a daily basis
• Both acute and chronic sleep loss can have detrimental effects on performance
• Deficits in executive functions can lead to critical errors in the work place
SLEEP LOSS
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“If you don’t think fatigue wreaks havoc, take a look at some of the laws we write around here at 1 a.m.”
-Rep. James Oberstar (D-MN)
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• Coast Guard
• Federal Rail Road Administration
• Federal Motor Carrier Administration
• Federal Aviation Administration
• Health Care- ACGME
FATIGUE RISK MANAGEMENT
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• No specific Regulations at this time
• Rail Safety Improvement Act of 2008 (RSIA) requires railroads to develop –Risk Reduction Program–Fatigue Management Plan
RAIL ROAD
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• Total hours of service (HOS) per week = 70• Daily driving limit = 11• Continuous driving limit = 8 (30 minute break)• Two nights’ rest (1:00 am to 5:00 am)/week • 34 consecutive hours of rest to restart• Company penalties- $11,000 per offence• Driver Penalty- $2,75 per offence.
TRUCK DRIVERS
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• Varying flight and duty requirements based on what time the pilot’s day begins.• Flight duty period• Flight time limits of 8-9 hours• 10-hour minimum rest period• Cumulative Flight duty and flight Time limits• Fitness for duty• Fatigue risk management system
AVIATION
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• 16 hr duty hour limit for 1st year of residency• 24 hr limit for subsequent years of residency• Strategic napping encouraged• 10 hrs off in between duty periods• 24 hrs off per 7-day period• 80 hour limit per week • Flexibility depending on specialty
RESIDENT DUTY HOURS
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• Predicts risk of impairment in a given schedule
• Function as a component of fatigue risk management systems that are mandated by law
• Guide the effective implementation of fatigue countermeasures
• Allow more flexible and more effective scheduling then hours of service regulation
FATIGUE MODELING
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• Military
• Health Care
• Manufacturing
• First Responders (EMS, Police, Fire Fighters)
• Education
• Sports
POTENTIAL APPLICATIONS
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• Develop non-intrusive tools to measure performance in the operational environment
• Develop inexpensive tools to measure sleep quality and quantity over sequential sleep periods
• Develop personalized fatigue management programs to reduce occupational risk and improve individual performance and well being.
FUTURE GOALS