Raghu Upender, MDAssistant Professor in Neurology Medical DirectorVanderbilt Sleep Disorders Center

Fatigue Science & SafetyOccupational Sleep Medicine

• None

DISCLOSURES

EXXON VALDEZ

DRIVINGWHEN

DROWSY

• 71,000 non-fatal injuries occur per year

• 1,550 fatal injures occur per year

• $12.5 billion in monetary losses

How can we mitigate the risk of human error in

future disasters?

• Define fatigue and sleep

• Review effects of Sleep loss

• Review sleep physiology

• Describe fatigue modeling

• Fatigue risk management

OUTLINE

Physical or mental “exhaustion arising from labor, exertion, or stress”

-Merriam-Webster Dictionary

FATIGUE DEFINITION

FATIGUE SEVERITY SCALE

Fatigue ≈ performance degradation

FATIGUE IN THE WORK PLACE

• 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

Doran SM, Van Dongen HPA, Dinges DF. Arch Ital Biol 2001;139:253-267.

PVT REACTION TIMES

Saper CB et al. Nature 437, 1257-1263 (27 October 2005)

ASCENDING AROUSAL SYSTEM

Saper CB et al. Nature 437, 1257-1263 (27 October 2005)

SLEEP PROMOTING VLPO

Saper CB et al. Nature 437, 1257-1263 (27 October 2005)

FLIP FLOP SWITCH

• 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

• 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

Wesensten NJ, Thorne DR, et. Al. Aviat Space Environ med 2004;75:520-525

PVT SPEED AND SLEEP DEPRIVATION

• Process S

• Process C

SLEEP – WAKE REGULATION

–Sleep homeostatic drive

– Increases during the wake period

–Declines during sleep

–Quantified by slow wave sleep

PROCESS S

Taber KH et al. The Journal of Neuropsychiatry and Clinical Neurosciences 2006

CEREBRAL BLOOD FLOW ACROSS SLEEP STATES

PERFORMANCE RESERVOIR

http://dnr.wi.gov/org/water/wm/dsfm/dams/gallery.html

• Master Circadian oscillator

• Provides alerting signal

PROCESS C

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

PROCESS WPROCESS OF AWAKENING

Balkin, TJ et al. Brain 2002;125:2308-2319

• 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

 

FATIGUE MODEL

Belenky, G et. al. J Sleep Res. 2003 Mar;12(1):1-12.

PVT SPEED AND SLEEP TIME

Hursh SR. Aviat Space Environ Med 2004; 75:A44-53

FATIGUE VS. ACCIDENT RISK

Hursh SR et al. SAE Trans 2004;113:111-119.

“I’m too tired to listen to a story right now, mom. Just e-mail something and I will read it tomorrow.”

• 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

“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)

• Coast Guard

• Federal Rail Road Administration

• Federal Motor Carrier Administration

• Federal Aviation Administration

• Health Care- ACGME

FATIGUE RISK MANAGEMENT

• 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

• 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

• 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

• 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

• 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

• Military

• Health Care

• Manufacturing

• First Responders (EMS, Police, Fire Fighters)

• Education

• Sports

POTENTIAL APPLICATIONS

• 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