Chronobiology of Sleep: Rhythms and Disorders

• Chronobiology of Sleep focuses on understanding sleep through biological rhythms.

Objectives

• The aim is to grasp basic concepts of sleep chronobiology.
• Defining night owl, morning person, jet lag, sleep debt, and dream enacting behaviors is important.
• Focus is on discussing the fundamentals of sleep chronobiology.
• Understanding the epidemiology and evaluation of different sleep-wake disorders is an objective.
• Sleep disorders include Insomnia, Hypersomnolence, Narcolepsy, and Breathing-Related disorders like Obstructive and Central Sleep Apnea.
• Other disorders include Circadian Rhythm Sleep-Wake Disorders and Parasomnias such as Non-Rapid Eye Movement Sleep Arousal Disorders.
• Also includes Rapid Eye Movement Sleep Behavior Disorder, Restless Legs Syndrome, and Substance/Medication-Induced Sleep Disorder.
• Evaluate etiological factors, considering both biological and psychosocial elements.
• Describing epidemiological factors that are linked to various sleep disorders.
• Ability to compare and contrast different sleep stages.
• Describing sleep hygiene measures for better sleep.
• Taking a complete sleep history from patients.
• Recommending diagnostic tests such as polysomnography and Multiple Sleep Latency Test.

Glossary

• Night owls experience late onset sleep and wake up late in the morning.
• Morning people have early onset sleep and wake up early.
• Sleep debt refers to the consequences of not getting enough sleep.
• Jet lag is a condition affecting frequent travelers across multiple time zones.
• Dream enacting behaviors involve motor responses to the content of action-filled or violent dreams, especially when being attacked or trying to escape a threatening situation.

Chronobiology

• Branch of biology examining the effects of biological rhythms on life processes.

Biological Rhythm Types

• Circadian rhythms occur approximately every 24 hours, like core body temperature, metabolic activity, serum cortisol, and the sleep-wake cycle.
• Ultradian rhythms happen in less than 24 hours, such as the 180-minute growth hormone and 90-minute REM sleep cycles.
• Infradian rhythms occur over more than 24 hours, for example, menstrual and reproductive cycles.

Zeitgeber

• Zeitgebers are external cues synchronizing an organism's biological rhythm with the environment.
• Examples of zeitgebers include the day/night cycle, physical activity, melatonin levels, cortisol levels, and body temperature.

Circadian Rhythm

• The suprachiasmatic nucleus in the hypothalamus prompts the pineal gland to produce melatonin when light decreases and inhibits its secretion when light increases.

Orexin / Hypocretin

• A hypothalamic neuropeptide maintaining sleep/wakefulness states.
• Cell bodies are in the dorsolateral hypothalamus, projecting to areas like the locus coeruleus, dorsal raphe nuclei, amygdala, and SCN.
• Orexin-A strongly promotes wakefulness, increases body temperature and locomotion, and increases energy expenditure.

Biological Clock Key Functions

• Peak coordination occurs around 14:30.
• Fastest reaction time is approximately 15:30.
• Greatest cardiovascular efficiency and muscle strength are around 17:00.
• Highest blood pressure is about 18:30.
• The body's temperature peaks around 19:00.
• Melatonin secretion starts at roughly 21:00.
• Bowel movements are suppressed at 22:30.
• Deepest sleep occurs around 02:00.
• Lowest body temperature is at 04:30.
• Sharpest rise in blood pressure is around 06:45.
• Melatonin secretion stops around 07:30.
• Bowel movements are likely at 08:30.
• The highest testosterone secretion is around 09:00.
• High alertness is around 10:00.

Stages of Sleep Architecture

• Sleep cycles include distinct stages like N1, N2, N3, and REM.
• N1 is the stage of light sleep.
• N2 is another light sleep stage.
• N3 is deep sleep.
• REM sleep is associated with vivid dreaming.

Hypnogram

• A normal sleep hypnogram illustrates sleep stages over time, including wakefulness, REM, and stages 1-4.
• Sleep cycles typically last between 70 and 120 minutes.

Sleep Stages (Brain Waves)

• When awake and relaxed, alpha waves are present.
• Stage 1 sleep is characterized by alpha waves.
• Stage 2 sleep has sleep spindles, which are bursts of activity observed on an EEG along with K-complexes.
• Stage 3 sleep features delta waves.
• Delta waves also occur during Stage 4 sleep.
• REM sleep includes sawtooth patterns and is correlated with eye movement.

Sleep Physiology

• Non-REM sleep involves decreased adrenergic and cholinergic activity.
• The ventrolateral preoptic area controls non-REM sleep.
• The brain is very active during REM sleep with discharges from the Pontine Reticular Formation.
• The Perilocus Ceruleus inhibits motor activity during REM sleep.
• Sensory input is inhibited during REM sleep.

Sleep duration for different age groups:

• Newborns (0-3 months) need 14-17 hours.
• Infants (4-11 months) need 12-15 hours.
• Toddlers (1-2 years) need 11-14 hours.
• Preschoolers (3-5 years) need 10-13 hours.
• School-age children (6-13 years) need 9-11 hours.
• Teenagers (14-17 years) need 8-10 hours.
• Young adults (18-25 years) and adults (26-64 years) need 7-9 hours.
• Older adults (65+) need 7-8 hours of sleep.

Age-Appropriate Sleep Averages

• 6-month-olds need 11 hours of nighttime sleep and 3.5 hours of daytime sleep.
• 1-year-olds need 12 hours of nighttime sleep and 2 hours during the day.
• 2-year-olds need 11.5 hours at night and 2 hours during the day.
• 3-year-olds require 11 hours at night and 2 hours during the day.
• 4-year-olds need 11 hours at night and 1 hour during the day.
• 6 and 8-year-olds need 11 and 10.5 hours of nighttime sleep, respectively, with no daytime sleep.
• 10-year-olds need 10 hours of nighttime sleep.
• 13-year-olds need 9 hours, and those 16 years and up need 8 hours of nighttime sleep.

Sleep Disorders Epidemiology

• 50% of outpatient primary care patients report sleep issues.
• Sleep problems are more prevalent in patients with psychiatric conditions.
• Insomnia is more frequent among psychiatric patients, the elderly, women, and individuals with limited education, lower income, and multiple medical problems.
• Sleep apnea is more common in overweight patients.

Prevalence of Sleep-Wake Disorders

• Insomnia affects 10-15% of the population with a female to male ratio of 1.4:1.
• Hypersomnolence disorder affects 1% of the population with an equal female to male ratio.
• Narcolepsy affects 0.02-0.04% with an equal female to male ratio.
• Breathing-related sleep disorders affect 20% with a female to male ratio of 1:2 to 1:4.
• Circadian rhythm sleep-wake disorders affect 11%.
• Parasomnias affect 1-5%.
• Restless leg syndrome affects 1-2% with a female to male ratio of 2:1.
• Substance/medication-induced sleep disorder affects 0.38-0.5%.

Sleep Assessment Questions

• Usual sleep pattern needs to be assessed.
• Characteristics of any sleep disturbance experienced.
• Understand the clinical path.
• Assessment of the 24-hour sleep-wake cycle.
• History of sleep disturbances, including childhood occurrences and times of stress.
• Information from collateral sources when available.
• Asking about medication history.
• Details on illicit drug use.
• Consumption of alcohol, tobacco, and stimulants.
• Use of hypnotics.
• Over-the-counter substances used.
• Presence of medical disorders, family history, and history of sleep disorders.

Evaluation Tests

• Polysomnography includes electroencephalography, electrooculography, and electromyography.
• Polysomnography findings include 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 setting during the day.
• The Multiple Sleep Latency Test involves five scheduled naps for 20 minutes every 2 hours during wakefulness.
• A sleep onset of less than 5 minutes is considered pathologic.

Sleep Hygiene Recommendations

• Maintain a regular sleep routine and avoid naps.
• Limit staying in bed awake to only 5-10 minutes.
• Avoid watching TV or reading in bed.
• Drink caffeinated drinks with caution.
• Avoid substances that interfere with sleep and exercise regularly.
• Keep a quiet and comfortable bedroom and have a comfortable bedtime routine.
• Hide the clock if you tend to watch it at night.