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Shift Work and Sleep

Shift Work and Sleep. Objectives. Overview: sleep - circadian rhythms Describe perils of sleep restriction Address hazards of misaligned sleep Review some strategies to combat sleep misalignment – restriction in shift workers.

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Shift Work and Sleep

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  1. Shift Work and Sleep

  2. Objectives • Overview: sleep - circadian rhythms • Describe perils of sleep restriction • Address hazards of misaligned sleep • Review some strategies to combat sleep misalignment – restriction in shift workers “Shifting Times” The Perils of Shift Work. Canadian Centre For Policy Alternatives. 2007. Saskatchewan Office

  3. Sleep Midnight 7:00 AM Temporal zone for sleep EEG Brain Waves

  4. Sleep: Essential Human Need • Alertness: consumes brain energy • (↑ 20% during course of the day) • Learning: neural synapses require energy, space • Sleep: like a nightly I.T. review! • “Re-organize”: ↓ energy needs, “space” in brain (erase unneeded neural nets) • “Re-charge”: stores brain energy (glycogen) • “Consolidate”: memory (preserves crucial neural networks, stores long term memory) Tononi, G. Sleep function and synaptic homeostasis. Sleep Med Rev. 10: 49-62, 2006.

  5. Sleep: Not a Societal Priority • To-day: average nocturnal sleep, 6.9 hr/night • 1/5th of adults now sleep < 6.5 hrs/night • Chronic, partial sleep restriction is common • Current average sleep duration: ↓ by 20% in last 100 years • “Optimal” sleep time: 8.2 hr/night • Average day worker is sleep-restricted by 1.3 hrs Banks S, DF Dinges. J. Clin. Sleep , Med. 2007; 3;519-28.

  6. What Happens If We Restrict Sleep? • 4-5 hrs nocturnal sleep: 1- 2 weeks, normal subjects: • Sleep “debt” accumulates; no adaptation • Alertness (performance) deteriorates steadily • 1 - 2 weeks later: significant brain dysfunction develops; equivalent to no sleep for 1-3 nights • BUT subjects think they are “doing fine” • 7 hours sleep is needed to maintain vigilance • Not everyone affected to the same degree Banks S, DF Dinges. J. Clin. Sleep Med. 2007; 3; 519-28.

  7. Sleep Restriction: As Risky As AlcoholImpairment! • Acute sleep loss (4hr/night for 1 night): • Marked ↓ performance (vigilance tests): • Effect: like a blood alcohol of .095 % • Legally impaired (similar to 5 beer) • Exaggerates effects of concurrent alcohol consumption T. Roerhrs et al. Sleep 23: 981, 2003

  8. Chronic Sleep Loss • The World Is Losing Sleep: Why? • Electric lighting, industrialized society • Work stress: around-the-clock culture (24/7/365) • Emphasis: “productivity” • On-call schedules; long commutes to work • Shift work: up to 1/3rd of work force Permanent nights; rotating shifts: 6.5% of work force • Night work: particularly hazardous temporal environment for human activity

  9. Shift Work • Many definitions: • “At least ½ of the work shift is outside standard work time (8:00 AM - 5:00 PM)”

  10. Industries Involving Shift Work • Service Industry: hotel, food, travel services • Transportation: (trucks, rail, air, taxi, commuters) • Hospital: (health, allied health) • Farmers, industrial workers, consumer goods • Communication, entertainment industries • Public protection: police, firefighters, air traffic control, military • Business travel (jet lag) “Shifting Times” the Perils of Shift Work. Canadian Centre For Policy Alternatives.2007. Saskatchewan Office

  11. Why Circadian Rhythms? • Brain: not engineered for round-the-clock alertness • Awake: sustained cortical activity leads to “brown-out” • Asleep: downtime for restoring energy, organization/repair • Circadian rhythms: ecologically “safe” downtime • Consolidate sleep- wakefulness into discrete blocks of time • Optimizes alertness (body-brain function) during the day • Consolidates sleep at night (safe temporal sleep environment) • Body’s cardiovascular, metabolic/molecular functions also regulated about the day

  12. Shift Workers: Sleep Is Both Restricted and Misaligned “SAFE” temporal zone for sleep; “HAZARDOUS” for work Midnight 7:00 AM Brain Waves

  13. Circadian Rhythms: Sleep Alignment • What regulates circadian rhythms? • Environmental conditions • Endogenous factors

  14. Chronobiology: Biological Rhythms DAY NIGHT Heliotropes: leaves respond to sunlight Jean Jacque d’Ortous de Mairan. Paris; 1729

  15. Constant Darkness NO LIGHT BY DAY NIGHT

  16. Circadian Rhythm: Endogenous (Independent of Light-Dark Cycle)

  17. Intrinsic Circadian Rhythms: Independent of Environmental Cues “Constant Routine”: No environmental (light – dark cues) Cyclic rhythms persist (free running) Intrinsic free-running rhythm (24.2 hrs)

  18. Melatonin: Opens the Sleep Gate What time is it in the brain? Constant routine Czeisler, CA. NEJM. 332; 6-11, 1995

  19. Brain’s Master Clock (Timekeeper) “Zeitgebers” (time givers) “entrain” clock Master clock: Suprachiasmatic nucleus LIGHT EYE Anterior hypothalamus EXERCISE FOOD, SOCIAL

  20. The Brain’s Master Clock “Zeitgebers” (time givers) “entrain” clock Regulates: - Hormones - Sleep/wake - Temp Pineal Gland Master clock: Suprachiasmatic nucleus LIGHT EYE EXERCISE FOOD, SOCIAL

  21. The Brain’s Master Clock: Night Regulates: - Hormones - Sleep/wake - Temp Pineal Gland Master clock: Suprachiasmatic nucleus No LIGHT EYE AM Sleep (night) Melatonin “phase marker”

  22. The Brain’s Master Clock: Day “Zeitgebers” (time givers) “entrain” clock Regulates: - Hormones - Sleep/wake - Temp Pineal Gland Master clock: Suprachiasmatic nucleus LIGHT EYE PM Wake (day) EXERCISE FOOD, SOCIAL No Melatonin

  23. Two-Process Model: Homeostatic Sleep vs Circadian Alerting “Drives” Homeostatic Sleep Signal Sleep zone LEVEL OF ALERTNESS Awake zone Circadian Awake Signal 9 AM Day time 9 PM Night time 9 AM

  24. OVERVIEW: TYPES OF SLEEP LOSS • (Voluntary) sleep restriction • ↓ nocturnal sleep duration • Discontinuous (fragmented) sleep • (Interrupted sleep – adequate total sleep time) • Misalignment of sleep (Shift Work) • Work – sleep cycle is out of phase with endogenous biological (circadian) clock

  25. Causes of Restricted/Fragmented Sleep • Voluntary sleep Loss (Common) • Primary Sleep Disorders:obstructive sleep apnea (OSA), insomnia, shift work sleep disorder, movement disorders, narcolepsy • Secondary sleep disorders:nocturia, chronic pain, neurological, psychiatric, respiratory, cardiac • Others:drugs; environmental; domestic family, pets

  26. Sleep In Shift Workers “Larks” Circadian Clock Time SLEEP TIME “Night Owls” WORK TIME

  27. Circadian Clock: Hazardous For Night Work Pineal Gland Master clock: Suprachiasmatic nucleus ↓ LIGHT EYE A.M. Night Work (Sleepy) Melatonin

  28. Circadian Clock: Opposes Day Sleep Pineal Gland Master clock: Suprachiasmatic nucleus LIGHT EYE P.M. Day (Can’t sleep) EXERCISE FOOD, SOCIAL Melatonin (suppressed)

  29. Predictors of Poor Adaptation To Shift Work • Large sleep need (> 9 hrs) • Age > 50 years • Diurnal preference: “Larks” (“Night Owls” do better) • Heavy domestic responsibilities • Long commute times • Working a second job “moonlighting” • Extended overtime work schedule: no time to sleep • Co-morbid medical conditions: • Primary/Secondary sleep disorders

  30. Shift Work Sleep Disorder • Distinction with normal response: blurred • Formal diagnostic term not commonly used • Validity of diagnostic category (AASM) needs testing • Important to R/O other sleep disorders • Prevalence: up to 10% of shift workers • Symptoms: • Sleepy during night work in 50% (5:00 – 7:00 AM) • Insomnia when trying to sleep (by day) • Marked individual (genetic) vulnerability Drake, C. Sleep. 27: 1454-62, 2004 Sack, R.L. et al Sleep. 30;1460-83, 2007

  31. Shift Work Sleep Disorder • Not “solely” a circadian rhythm issue • Interaction of several factors: • Misalignment of sleep - wake behavior, with the circadian clock (light-dark cues oppose behavior) • Sleep restriction- disruption (can’t maintain sleep) • Social stresses, domestic responsibilities

  32. Sleep In Shift Workers • Shift workers ARE sleep restricted: • Day sleep is < 6 hrs (rapid sleep onset; lose REM; II) • Night workers: 10 hours less sleep/week than day workers • Night workers report: • Difficulty (maintaining) sleep by day • Sleepiness/falling asleep unintentionally at work, on commute home (60-70%)

  33. Consequences of Shift Work: Work Safety • Societal catastrophes: Exxon Valdez, Three Mile Island, Challenger accident • Medical trainees: fatigue-related errors (41%) • Policing: unsafe risks (44%) • Extended work hours (↑ accidents/injury 2-3 fold): • Risk of accidents: ↑ in early AM; mid afternoon • Commute home: dangerous • Loss of consciousness: account for 27% of road crashes – but 83% of highway deaths!

  34. Consequences Of Shift Work: Medical Illness • Shift workers are at increased risk for: • All cause mortality (Nurses Health Study) • Stomach ulcers (↑4 fold) • Cancer (colorectal, breast) • Insulin resistance; metabolic syndrome • (↑ Bp, diabetes, obesity, ↑ lipids) • Coronary artery disease (nurses Health Study) Dinges, D. et al. Principles and Practice of Sleep Medicine. 4th Edition. Chapter 6, page 67-75, 2005

  35. Consequences Of Shift Work: Medical Illness • Shift workers are at increased risk for: • Increased sick time (higher inflammatory mediators, lower immune function) • Depression/OSA/GERD • Automobile crashes, work accidents • Reduced Quality of Life: • ↑ Risk of marital break-up • Less social activity (family, friends) Dinges, D. et al. Principles and Practice of Sleep Medicine. 4th Edition. Chapter 6, page 67-75, 2005

  36. Combating Shift Work Sleep Disorder: Two Approaches • Strategy one: phase “shift” circadian clock • Often not practical • Most night workers do not shift circadian clock • Zeitgebers (light) oppose circadian phase shift • Phase shifts (when they occur) are slow (90 min/night) • Phase shift must be maintained on days off • Strategy two: don’t try to phase shift circadian clock • Adjust work schedule/sleep accordingly • Optimize/protect time for sleep on night shift

  37. Combating Shift Work Sleep Disorder • No “Magic Bullet” - numerous factors to consider: • Operational needs of the work place • Individual factors: primary - secondary sleep disorders • Human biology: inherently sleepy at night • Institutional factors • Economics (for worker, society, industry) • Solutions: • Dialogue among workers, management, society

  38. Combating Shift Work Sleep Disorder • Improving alertness at night • Safe, cool, brightly lit work environment • Planned naps: 2 hours (before night shift) • Mid Shift Nap (2 - 4 AM) for 30-50 min • Timed light exposure (1-2,000 Lux) during first half of night shift Sack, RL et al Sleep. 30; 1460-83, 2007 Morgenthaler, TIA. .A.S.M. Report Sleep. 30: 1445-59,2007

  39. Combating Shift Work Sleep Disorder • Improving alertness at night • Alertness promoting/stimulant medications: strategic use at beginning of night shift • Caffeine (300 mg) at 1-2 AM • Modafinil (100 – 200 mg): Just before night shift (alertness ↑ by 50%; effect equivalent to 600 mg of caffeine) • Modafanil did not restore alertness to day time levels • Recently received U.S. FDA approval for shift work sleep disorder

  40. Combating Shift Work Sleep Disorder • Protect/improve day sleep: • Low AM light (dark sunglasses for trip home) • Short commutes home from work • Sleep hygiene: “protect” day sleep • Avoid alcohol, tobacco (caffeine) • Go to bed early after night shift • Completely dark, cool, quiet bedroom (no phone) • Social/family support (let mom/dad sleep!)

  41. Combating Shift Work Sleep Disorder • Protect/improve day sleep • Avoid sedative/hypnotics (tolerance, dependence, carry-over sedation at work) • Improves day sleep on 1st AM sleep: - no effect on night time alertness (Triazolam, Zopiclone 30-60 min before AM sleep) • Melatonin (2-3 mg prior to daytime sleep) • Improves sleep duration (first day); little effect on alertness during work • Ramelteon (melatonin receptor agonist): role in shift workers not defined

  42. Combating Shift Work Sleep disorder • Work schedules: • Strategy 1: shift circadian clock: night alertness, day sleep • Time resynchonization takes up to 1 week • Quickly reverts to daytime clock function on days off • Strategy 2: do not shift circadian clock • “Continental” (rapid shift rotations) • Combat circadian misalignment (night fatigue-day insomnia) • Δ shifts forward: 2 days; 2 evenings; 2 nights; off • Limit night shifts to < 4 consecutive nights

  43. Night Worker - To “Shift” Clock Time Evening Light: AM Melatonin Evening Light: Shifts Clock to daytime Sleep, in night shift workers Melatonin “Larks” SLEEP TIME Sleep Phase (Day worker) “Night Owls” Good Moves sleep propensity to a later time (day) Light (Subjective Dusk)

  44. Night Worker: Avoid Morning Light Exposure Morning light: Clock remains synchronized to night time sleep in night shift Workers “Larks” SLEEP TIME Sleep Phase (Day worker) “Night Owls” Bad Moves sleep propensity to earlier time (night) Light (Subjective Dawn)

  45. Shift Work and Sleep: Summary • Sleep: Essential for optimal alertness, learning, memory, judgment, physical health • Sleep loss/circadian sleep misalignment: pose serious hazards for workers/industry/society • Solutions: shared responsibility (employer, society, worker) • Achieving “tolerance” to shift work: • Recognize circadian sleep-wake misalignment • Protect adequate time for sleep time (> 7 hours) • Address social/domestic/work schedule factors

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