Chronobiology of Sleep

Chronobiology of Sleep

• Chronobiology is the biology branch studying the effects of biological rhythms on essential life processes.

Biological Rhythm Types

• Circadian rhythms fluctuate over approximately 24 hours, examples include core body temperature, metabolic activity, serum cortisol, and the sleep-wake cycle
• Ultradian rhythms fluctuate in less than 24 hrs, examples include growth hormone release and the 90 min REM sleep cycle
• Infradian rhythms fluctuate in over 24 hrs, one example is menstrual and reproductive cycles

Zeitgeber

• Zeitgebers are external or environmental cues synchronizing an organism's biological rhythm to the environment.
• Examples: day/night cycle, physical activity, melatonin, cortisol, and body temperature levels.

Circadian Rhythm

• Suprachiasmatic nucleus cells in the hypothalamus induce the pineal gland to produce melatonin when light decreases.
• The suprachiasmatic nucleus cells also inhibit melatonin secretion when light increases.

Orexin / Hypocretin

• Orexin/Hypocretin is a hypothalamic neuropeptide that maintains sleep/wakefulness states.
• Cell bodies are located in the dorsolateral hypothalamus

Action of Orexin-A

• Orexin-A is administered centrally, and strongly promotes wakefulness.
• Orexin-A increases body temperature and locomotion.
• Orexin-A elicits a strong increase in energy expenditure.

Sleep Architecture: Sleep cycle

• Includes stages N1 (light sleep), N2, N3 (deep sleep) and REM (Rapid Eye Movement, vivid dreaming)
• A normal sleep hypnogram shows multiple sleep staged cycles over a sleep period

Sleep Stages & Brain Waves

• Awake and relaxed state is associated with Alpha waves
• NREM Sleep is comprised of Stages 1 to 4, characterized by decreased adrenergic and cholinergic activity and controlled by the Ventrolateral preoptic area.
• REM sleep involves a very active brain, discharges from the Pontine Reticular Formation, Perilocus Ceruleus inhibits motor activity and inhibited sensory input.

Sleep stage Distribution (Brain Waves)

• Awake and relaxed -> Alpha Waves
• Stage 1 Sleep - 3%
• Stage 2 Sleep - 50%, includes Spindle (burst of activity)
• Stage 3 Sleep - 10%, includes K-Complex
• Stage 4 Sleep - 15%, Delta waves
• REM Sleep - 22%, Sawtooth pattern, Eye movement phase

Sleep Duration

• Varies across the lifespan, with newborns needing the most sleep and older adults needing the least.

Age-Appropriate Sleep

• 6 mo: 11 hours nighttime and 3 ½ hours daytime sleep
• 1 yr: 12 nighttime and 2 hours daytime
• 2 yrs: 11 ½ nighttime and 2 hours daytime
• 3 yrs: 11 nighttime and 2 hours daytime sleep
• 4 yrs: 11 hours nighttime and 1 hour daytime sleep
• 6 yrs: 11 hours nighttime, with no daytime sleep
• 8 yrs: 10 ½ hours nighttime, with no daytime sleep
• 10 yrs: 10 hours nighttime, with no daytime sleep
• 13 yrs: 9 hours nighttime sleep, with no daytime sleep
• 16 yrs and up: 8 hours nighttime, with no daytime sleep

Epidemiology of Sleep Disorders

• 50% of outpatient primary care clinic patients report sleep problems.
• Sleep disorders are higher in patients with psychiatric conditions.
• Insomnia is more frequent in psychiatric patients, the elderly, women, those with limited education, those with lower incomes and people with multiple medical problems.
• Sleep apnea is more common in overweight patients.

Sleep-Wake Disorders

• Insomnia affects to 10-15% of the population with a female to male ratio of 1.4:1
• Hypersomnolence affects to 1% of the population with a female to male ratio of 1:1
• Narcolepsy affects to 0.02-0.04% of the population with a female to male ratio of 1:1
• Breathing related sleep disorders affects to 20% of the population, female to male ratio ranges from 1:2 to 1:4
• Circadian rhythm sleep-wake disorders affects to about 11% of the population
• Parasomnias, sleep disorders that include abnormal movements, emotions, perceptions, dreams, and autonomic functions, affects around 1-5% of the population
• Restless legs syndrome affects 1-2% of the population with a female to male ratio of 2:1
• Substance / medication induced sleep disorder affects to 0.38-0.5% of the population

Sleep Assessment: Questions to ask

• Usual sleep pattern
• Characteristics of the sleep disturbance
• Clinical course
• 24-hour sleep-wake cycle
• Sleep disturbance history, including childhood and under stress
• Description by collateral if available
• Medication history
• Illicit drugs
• Alcohol/ tobacco / stimulants
• Hypnotics
• Over the counter substances
• Medical disorders
• Family history and sleep disorder history

Evaluation of Sleep Disorders

• Polysomnography uses EEG to measure electroencephalography, electrooculography and electromyography
• Polysomnography findings include sleep continuity and architecture, REM physiology, sleep-related breathing, oxygen desaturation, cardiac arrhythmias and periodic movements.
• Multiple Sleep Latency Test measures how quickly a patient falls asleep in a quiet environment the day, consists of five scheduled naps for 20 minutes every 2 hours during wakefulness; Falling asleep in < 5 min is considered pathologic

Sleep Hygiene Practices

• Maintain a regular sleep routine.
• Avoid naps if possible.
• Avoid staying in bed awake for more than 5-10 minutes.
• Avoid watching TV or reading in bed.
• Avoid caffeinated drinks.
• Avoid substances that interfere with sleep.
• Exercise regularly.
• Have a quiet, comfortable bedroom.
• Follow a comfortable pre-bedtime routine.
• If being a 'clock watcher' at night, hide the clock.

Sleep Glossary

• Night owl: Late onset sleep and late waking in the morning.
• Morning person: Early onset sleep and early waking.
• Sleep Debt: Consequences of getting less than an optimal amount of sleep.
• Jet lag: Condition that affects people who travel frequently and across multiple time zones.
• Dream Enacting Behaviors include motor responses to content of action-filled or violent dreams of being attacked or trying to escape threatening situations.