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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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Objectives
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


Sleep
Sleep

Midnight

7:00 AM

Temporal zone for sleep

EEG Brain Waves


Sleep essential human need
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.


Sleep not a societal priority
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.


What happens if we restrict sleep
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.


Sleep restriction as risky as alcohol impairment
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


Chronic sleep loss
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


Shift work
Shift Work

  • Many definitions:

  • “At least ½ of the work shift is outside standard work time (8:00 AM - 5:00 PM)”


Industries involving shift work
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


Why circadian rhythms
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


Shift workers sleep is both restricted and misaligned
Shift Workers: Sleep Is Both Restricted and Misaligned

“SAFE” temporal zone for sleep; “HAZARDOUS” for work

Midnight

7:00 AM

Brain Waves


Circadian rhythms sleep alignment
Circadian Rhythms: Sleep Alignment

  • What regulates circadian rhythms?

    • Environmental conditions

    • Endogenous factors


Chronobiology biological rhythms
Chronobiology: Biological Rhythms

DAY

NIGHT

Heliotropes:

leaves respond

to sunlight

Jean Jacque d’Ortous de Mairan. Paris; 1729


Constant darkness
Constant Darkness

NO LIGHT BY DAY

NIGHT



Intrinsic circadian rhythms independent of environmental cues
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)


Melatonin opens the sleep gate
Melatonin: Opens the Sleep Gate Cues

What time is it in the brain?

Constant routine

Czeisler, CA. NEJM. 332; 6-11, 1995


Brain s master clock timekeeper
Brain’s Master Clock (Timekeeper) Cues

“Zeitgebers” (time givers) “entrain” clock

Master clock:

Suprachiasmatic nucleus

LIGHT

EYE

Anterior hypothalamus

EXERCISE

FOOD, SOCIAL


The brain s master clock
The Brain’s Master Clock Cues

“Zeitgebers” (time givers) “entrain” clock

Regulates: - Hormones - Sleep/wake - Temp

Pineal Gland

Master clock:

Suprachiasmatic nucleus

LIGHT

EYE

EXERCISE

FOOD, SOCIAL


The brain s master clock night
The Brain’s Master Clock: Night Cues

Regulates: - Hormones - Sleep/wake - Temp

Pineal Gland

Master clock:

Suprachiasmatic nucleus

No LIGHT

EYE

AM

Sleep (night)

Melatonin “phase marker”


The brain s master clock day
The Brain’s Master Clock: Day Cues

“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


Two process model homeostatic sleep vs circadian alerting drives
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


Overview types of sleep loss
OVERVIEW: TYPES OF SLEEP LOSS “Drives”

  • (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


Causes of restricted fragmented sleep
Causes of Restricted/Fragmented Sleep “Drives”

  • 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


Sleep in shift workers
Sleep In Shift Workers “Drives”

“Larks”

Circadian Clock Time

SLEEP TIME

“Night Owls”

WORK TIME


Circadian clock hazardous for night work
Circadian Clock: Hazardous For Night Work “Drives”

Pineal Gland

Master clock:

Suprachiasmatic nucleus

↓ LIGHT

EYE

A.M.

Night Work

(Sleepy)

Melatonin


Circadian clock opposes day sleep
Circadian Clock: Opposes Day Sleep “Drives”

Pineal Gland

Master clock:

Suprachiasmatic nucleus

LIGHT

EYE

P.M.

Day (Can’t sleep)

EXERCISE

FOOD, SOCIAL

Melatonin (suppressed)


Predictors of poor adaptation to shift work
Predictors of Poor Adaptation To Shift Work “Drives”

  • 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


Shift work sleep disorder
Shift Work Sleep Disorder “Drives”

  • 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


Shift work sleep disorder1
Shift Work Sleep Disorder “Drives”

  • 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


Sleep in shift workers1
Sleep In Shift Workers “Drives”

  • 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%)


Consequences of shift work work safety
Consequences of Shift Work: Work Safety “Drives”

  • 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!


Consequences of shift work medical illness
Consequences Of Shift Work: Medical Illness “Drives”

  • 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


Consequences of shift work medical illness1
Consequences Of Shift Work: Medical Illness “Drives”

  • 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


Combating shift work sleep disorder two approaches
Combating Shift Work Sleep Disorder: Two Approaches “Drives”

  • 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


Combating shift work sleep disorder
Combating Shift Work Sleep Disorder “Drives”

  • 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


Combating shift work sleep disorder1
Combating Shift Work Sleep Disorder “Drives”

  • 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


Combating shift work sleep disorder2
Combating Shift Work Sleep Disorder “Drives”

  • 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


Combating shift work sleep disorder3
Combating Shift Work Sleep Disorder “Drives”

  • 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!)


Combating shift work sleep disorder4
Combating Shift Work Sleep Disorder “Drives”

  • 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


Combating shift work sleep disorder5
Combating Shift Work Sleep disorder “Drives”

  • 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


Night worker to shift clock time evening light am melatonin
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)


Night worker avoid morning light exposure
Night Worker: Avoid Morning Light Exposure Melatonin

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)


Shift work and sleep summary
Shift Work and Sleep: Summary Melatonin

  • 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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