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SLEEP PHYSIOLOGY — COMPLETE TEXTBOOK NOTES

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1. Introduction to Sleep

• 50% of US adults experience intermittent sleep disturbance

• 50-70 million Americans suffer from chronic sleep/wakefulness disorders

• 80% remain undiagnosed, costing >$400 billion annually (Harrison's, 22nd Ed)

• Most adults require 7-9 hours per night for optimal function

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2. Definition and Characteristics of Sleep

Guyton & Hall: "Sleep is a state of unconsciousness from which a person can be aroused by sensory or other stimuli." Neuroscience: Exploring the Brain: "Sleep is a readily reversible state of reduced responsiveness to, and interaction with, the environment."

• Coma (not reversible by stimuli)
• Hibernation (seasonal metabolic suppression)
• General anesthesia (not readily reversible)

Two Major Types:

1. NREM Sleep - high-voltage, slow EEG; restful, quiet brain
2. REM Sleep - low-voltage, fast EEG; active, dreaming brain

Comparison Table (Neuroscience: Exploring the Brain):

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3. Functions of Sleep

1. Neural Restoration: Restores balance among CNS functional centers; restores normal levels of brain activity
2. Memory Consolidation:
   • REM sleep → procedural and emotional memory
   • N3 slow-wave sleep → declarative memory
3. Synaptic Homeostasis Theory (Tononi & Cirelli): Synaptic upscaling during wakefulness (BDNF, Arc gene activation); downscaling during sleep (removes unimportant synaptic connections, reduces energy cost)
4. Energy Restoration (Benington-Heller Hypothesis): Glial glycogen stores depleted during wakefulness; restored during sleep
5. Glymphatic Waste Clearance: Beta-amyloid and other metabolic waste products cleared 2× faster during sleep (requires low noradrenaline)
6. Oxidative Stress Repair: Antioxidant enzymes upregulated; DNA double-strand breaks (accumulated during wakefulness) repaired
7. Immune Regulation: Regulates inflammatory cytokines (IL-6, TNF-alpha); one night of partial sleep deprivation causes transcriptional changes mimicking accelerated aging
8. Growth and Development: Critical for neural maturation; GH released during N3
9. Metabolic/Thermoregulation: BP, RR, and BMR decrease 10-30% during NREM
10. Macromolecular Biosynthesis: Genes for cholesterol synthesis, heme synthesis, and protein synthesis are upregulated during sleep

Consequences of Sleep Deprivation:

• Irritability, cognitive impairment, psychosis (prolonged)
• Glucose intolerance, obesity, metabolic syndrome
• Cardiovascular disease, dementia risk
• Rats deprived 2-3 weeks die (Guyton & Hall)
• Reaction time slows; vigilance decreases

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4. Theories of Sleep

4a. Passive Theory (Historical - Disproven)

• RAS becomes fatigued during wakefulness → inactivity = sleep
• Disproven: Transecting brainstem at midpontile level → cortex never sleeps → an active center below the midpons must be causing sleep

4b. Active Inhibitory Theory (Current)

• Sleep is an active process driven by inhibitory sleep-promoting neurons
• VLPO neurons actively inhibit all arousal centers
• Stimulation of raphe nuclei → sleep; stimulation of nucleus tractus solitarius → sleep

4c. Humoral/Chemical Theory

• Muramyl peptide (from gut bacteria) - accumulates in CSF; induces sleep when injected into 3rd ventricle
• Delta-sleep-inducing peptide (DSIP) - isolated from CSF after thalamic stimulation
• Adenosine - byproduct of ATP metabolism; accumulates in basal forebrain and cortex during wakefulness; inhibits wake-promoting neurons; caffeine blocks adenosine receptors
• Prostaglandin D2 - activates sleep-promoting circuits

4d. Two-Process Model (Borbély, 1982)

• Process S (Homeostatic) + Process C (Circadian) together govern sleep timing and depth
• This is the dominant current model

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5. Classification of Sleep

NREM Sleep

• 75%-80% of total sleep time in adults
• 3 stages (AASM 2007 criteria): N1, N2, N3
• (Former Rechtschaffen & Kales 1968 criteria had 4 stages; stages 3 & 4 = now N3)
• "An idling brain in a movable body" (William Dement)

REM Sleep

• 20%-25% of total sleep in young adults
• Also called Paradoxical Sleep or Desynchronized Sleep
• First described in 1953 by Aserinsky and Kleitman
• "An active, hallucinating brain in a paralyzed body" (William Dement)
• Low-amplitude mixed-frequency EEG + rapid conjugate eye movements + skeletal muscle atonia

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6. Neural Control of Sleep

• Multiple structures in medulla, brainstem, hypothalamus, and basal forebrain are involved
• No single brain lesion produces permanent insomnia or permanent sleep → reflects redundancy

• Lesions at midbrain/diencephalon junction → profound sleepiness (20+ hours/day)
• Lesions in anterior hypothalamus → severe unrelenting insomnia
• This identified: posterior hypothalamus = arousal zone; anterior hypothalamus = sleep zone

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7. Anatomy of the Sleep-Wake Regulatory System

Ascending Arousal System - Key Nuclei:

Sleep-Promoting System - Key Nuclei:

Two Pathways of the Ascending Arousal System:

1. Dorsal pathway: Brainstem → thalamic relay nuclei → cortex
2. Ventral pathway: Brainstem → hypothalamus → basal forebrain → cortex (direct cortical activation)

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8. Ascending Reticular Activating System (ARAS)

• Lesions of midline brainstem → coma-like NREM-sleep state
• Electrical stimulation of midbrain tegmentum → cortical arousal (EEG desynchronization)

• Contains glutamatergic, cholinergic, aminergic, and hypocretinergic neurons
• Projects via two pathways to the cortex (dorsal through thalamus; ventral through hypothalamus/basal forebrain)

• Damage at rostral pons/lower midbrain → coma
• Isolated thalamic damage → loss of content of wakefulness (vegetative state), but sleep-wake cycles largely preserved

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9. Sleep-Promoting Centers

Ventrolateral Preoptic Nucleus (VLPO)

• Location: anterior hypothalamus, above the optic chiasm
• Neurotransmitters: GABA + galanin (both inhibitory)
• Neurons fire: slowest during waking → increase at sleep onset → fastest during deep sleep
• Projects to and inhibits ALL arousal centers (LC, TMN, raphe, PPT/LDT, orexin neurons)
• Called the "sleep switch" (Fishman's Pulmonary)
• Lesions → fragmented sleep, up to 50% reduction in total sleep
• Elderly: VLPO galanin neurons lost (contributes to fragmented sleep)
• Alzheimer's disease: VLPO neurons lost → poor sleep quality

Median Preoptic Nucleus (MnPO)

• GABAergic; fires higher during first sleep cycle (high sleep pressure); declines in later cycles
• Lesions → loss of up to half total sleep time
• Tracks "sleep pressure" (Process S)

Parafacial Zone

• GABAergic neurons near facial nerve nucleus in medulla
• Promotes NREM by inhibiting parabrachial nucleus (wake-promoting) → reduces glutamatergic drive to basal forebrain
• Lesions → loss of up to half total sleep time

MCH Neurons (Lateral Hypothalamus)

• Produce melanin-concentrating hormone (MCH)
• Promote REM sleep by inhibiting orexin neurons and vlPAG (REM-off neurons)

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10. Wake-Promoting Centers

1. Locus Coeruleus (LC) - Noradrenaline

• Fires hundreds of milliseconds before EEG switches from NREM to wake → causal role in arousal
• Upregulates plasticity-related genes (synaptic potentiation) during wakefulness
• NE promotes wakefulness, attention, arousal

2. Raphe Nuclei - Serotonin

• Activated during repetitive motor activity (locomotion, grooming), NOT during orienting to novel stimuli
• SSRIs → decrease sleep time, increase arousal, suppress REM

3. Tuberomammillary Nucleus (TMN) - Histamine

• Only source of histamine in the brain
• Projects to prefrontal cortex, basal forebrain, thalamus, brainstem
• Promotes wakefulness via H1 receptors
• Antihistamines → sedation (H1 blockade)
• Fires only at wake onset (slightly delayed compared to LC)

4. PPT/LDT Nuclei - Acetylcholine

• Fire high during wakefulness AND REM sleep (both activated states)
• Promote cortical activation via thalamus
• Also: basal forebrain cholinergic neurons (nucleus basalis, diagonal band of Broca) → excite entire cortex

5. Lateral Hypothalamus - Orexin/Hypocretin

• Most active during waking, especially during motor activity and exploratory behavior
• Fire before EEG activates on arousal (predictive/causal role)
• Completely silent during both NREM and REM sleep

6. VTA/Substantia Nigra - Dopamine

• Mean firing rate does not dramatically change across sleep-wake states
• Phasic bursting ↑ in REM and during reward
• Amphetamine/cocaine (DA reuptake blockers) → prolonged wakefulness

7. Basal Forebrain - Glutamatergic/GABAergic

• Bilateral lesions → coma
• GABAergic neurons inhibit cortical inhibitory interneurons → net arousal

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11. Neurotransmitters in Sleep and Wakefulness

Summary Table:

• REM-ON neurons (cholinergic, PPT/LDT) → activated during REM; activate EEG
• REM-OFF neurons (NE-LC, 5HT-raphe) → active during wake/NREM; silent before/during REM

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12. Orexin (Hypocretin) System

Discovery:

• Discovered simultaneously by two groups in 1998:
  • "Hypocretin" - hypothalamic incretin family (de Lecea)
  • "Orexin" - appetite-stimulating (Yanagisawa/Sakurai)
• Precursor peptide → cleaved into Orexin A (33 AA) + Orexin B (28 AA)

Location:

• Cell bodies exclusively in: lateral hypothalamic area (LHA), perifornical area, posterior hypothalamus
• Axons project widely throughout entire brain

Receptors:

Functions:

1. Stabilizes wakefulness (prevents state transitions - the "wake-state stabilizer")
2. Stimulates ALL wake-promoting systems: ACh, DA, NE, 5-HT, Histamine
3. Inhibits REM sleep
4. Regulates feeding, reward, autonomic function

Narcolepsy:

• Loss of orexin neurons → narcolepsy (unstable flip-flop switch → sleep attacks)
• Canine narcolepsy: Mutation in OX2R gene (Mignot, 1999)
• Orexin knockout mice: Narcoleptic phenotype (Yanagisawa, 1999)
• Human narcolepsy: 90%+ orexin neuron loss; CSF hypocretin-1 immeasurably low; HLA-DQB1*0602 genetic susceptibility; likely autoimmune (T-cell mediated; may follow H1N1 vaccination or infection)
• Clinical tetrad: Daytime sleep attacks, cataplexy (sudden emotional muscle weakness), sleep paralysis, hypnagogic/hypnopompic hallucinations
• Direct wake→REM transitions (SOREMPs = Sleep-Onset REM Periods) on MSLT

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13. Flip-Flop Switch Model

Concept (Proposed by Saper and colleagues):

Sleep-Wake Flip-Flop Switch:

• Monoaminergic nuclei (LC, TMN, raphe) → inhibit VLPO → VLPO cannot inhibit monoamines → self-reinforcing wake state
• Orexin reinforces monoaminergic tone (but no orexin receptors in VLPO - orexin acts only on wake side)

• VLPO fires → inhibits all monoaminergic nuclei + orexin neurons → removes monoaminergic inhibition of VLPO → self-reinforcing sleep state

NREM-REM Flip-Flop Switch:

• REM-ON and REM-OFF mutually inhibit each other
• Cholinergic input → promotes transitions TO REM
• Monoamines (NE, 5-HT) → excite REM-OFF → suppress REM (why antidepressants suppress REM)
• MCH neurons → inhibit REM-OFF → promote REM
• Orexin → excite REM-OFF → suppress REM

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14. Homeostatic Regulation of Sleep (Process S)

Neurochemical Basis - Adenosine:

• Metabolically active brain → consumes ATP → dephosphorylated to adenosine (neuromodulator)
• Adenosine accumulates in basal forebrain and cortex during prolonged wakefulness
• Adenosine → inhibits wake-promoting neurons (A1 receptors) + activates sleep circuits (A2a receptors → nucleus accumbens shell → hypothalamus → VLPO)
• Clears during sleep → low adenosine = refreshed

Evidence for Process S:

• Sleep deprivation → increased sleep latency speed, more intense slow-wave sleep (SWS) on recovery
• MnPO neurons fire highest during first cycle (peak sleep pressure) → decline through night
• Caffeine: Blocks A2a (primarily) and A1 receptors → delays sleep onset but does NOT reduce adenosine accumulation (sleep debt remains)

Clinical Measurement:

• MSLT (Multiple Sleep Latency Test): 4-5 nap opportunities, 2 hours apart; rested person takes >15-20 min; sleepy person falls asleep within 5 min; MSLT score <8 min = pathological sleepiness
• Psychomotor Vigilance Task (PVT): Reaction time test; most sensitive behavioral measure of sleepiness

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15. Circadian Regulation of Sleep (Process C)

Suprachiasmatic Nucleus (SCN) - The Master Pacemaker:

• Location: hypothalamus, directly above optic chiasm
• GABAergic neurons; most active during daytime in ALL mammals
• Isolated SCN neurons in culture maintain ~24-hour rhythms autonomously
• Intrinsic period: ~24.1 hours (slightly >24 hours → requires daily light entrainment to stay synchronized)

How SCN Regulates Sleep (Eric Kandel):

1. Light entrainment: Via retinohypothalamic tract (RHT) from intrinsically photosensitive retinal ganglion cells (ipRGCs) expressing melanopsin (not rods/cones) → synapse on SCN neurons → release glutamate + PACAP
2. Pineal pathway: SCN → paraventricular nucleus (PVN) → intermediolateral nucleus (IML) → superior cervical ganglion (SCG) → pineal gland → melatonin at night → promotes sleep
3. Hypothalamic relay: SCN → subparaventricular zone (SPZ) → dorsomedial hypothalamus (DMH):
   • DMH glutamatergic → excite orexin neurons → wakefulness
   • DMH GABAergic → inhibit VLPO → wakefulness

Circadian-Homeostatic Interaction:

• Circadian wake-promoting signal rises throughout the day to counterbalance rising Process S
• Peaks in late evening just before habitual bedtime → then collapses rapidly
• Lowest at hours before habitual wake time → helps maintain sleep even when Process S wanes
• Mismatch (shift work, jet lag) → inability to sleep/wake at wrong circadian time

Melatonin:

• Synthesized from serotonin in pineal gland; signals darkness
• Levels rise 2-4 hours before sleep onset (DLMO = dim-light melatonin onset = clinical biomarker)
• MT1 receptors in SCN → inhibit SCN → reduce wake-promoting signal
• MT2 receptors → phase-shift circadian rhythms
• Used clinically for: jet lag, non-24-hour sleep-wake disorder, delayed sleep phase

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16. Molecular Circadian Clock and Clock Genes

Core Clock Genes (Mammals):

Transcription-Translation Feedback Loop (~24 hours):

Clinical Implications:

Peripheral Clocks:

• Nearly EVERY cell (liver, kidney, lung, heart) has its own molecular circadian clock using the same CLOCK/BMAL1/PER/CRY loops
• SCN coordinates all via: ANS, core body temperature (~1°C drop each night), cortisol, feeding/locomotion cues

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17. Sleep Architecture

Key Facts:

• NREM and REM alternate in ultradian cycles
• Each cycle: ~90 minutes (range 60-160 min)
• 4-6 cycles per typical night
• First two cycles dominated by N3 (SWS); later cycles by REM
• Longest REM period (near morning) can last up to 1 hour

Stage Distribution in Young Adults:

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18. Normal Hypnogram

• X-axis: Time (hours)
• Y-axis: Sleep stage (Wake → REM → N1 → N2 → N3; deepest at bottom)

Normal Young Adult Pattern:

1. Sleep onset → rapid descent: N1 → N2 → N3 within 45-60 min
2. First REM period at ~60-90 minutes after sleep onset (short, ~10 min)
3. Cycles repeat ~every 90 min; 4-6 cycles total
4. First third of night: Dominated by N3 (SWS)
5. Last third of night: Dominated by progressively longer REM periods
6. Morning awakening typically from REM

Sleep Macrostructure Terms:

• Sleep efficiency = (Total sleep time / Time in bed) × 100%; normal >85%
• WASO = Wake After Sleep Onset
• Sleep latency = Time to first epoch of sleep

Sleep Microstructure (Bradley & Daroff):

• Arousals: Brief EEG frequency shifts; arousal index ≤10/hour = normal
• CAP (Cyclic Alternating Pattern): Repetitive EEG pattern during NREM; phase A (unstable, high amplitude) alternating with phase B (stable)

Pathological Deviations:

• Narcolepsy: Direct wake→REM (SOREMP - no preceding NREM)
• Depression: Short REM latency (<60 min); increased REM density; early morning awakening
• OSA: ↑↑ N1 (from ~5% to 30-50%); marked N3 reduction; frequent arousals

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19. Electroencephalography (EEG) in Sleep

EEG Basics:

• Records synchronous dendritic potentials from large populations of cortical pyramidal neurons
• Amplitude: typically 0-200 μV; frequency: 0.5-50+ Hz
• Standard electrode placement: 10-20 system

Cellular Mechanisms (Eric Kandel):

• Slow waves (NREM): Generated by intrinsic cortico-cortical recurrent circuitry → alternating "down states" (hyperpolarized, silent) and "up states" (depolarized, firing) → large dendritic potentials = slow waves visible on EEG
• Sleep spindles: Generated in thalamus - reticular nucleus neurons burst → hyperpolarize thalamocortical relay neurons → de-inactivate T-type Ca²⁺ channels → Ca²⁺ burst → relay cell fires → feedback to reticular nucleus → cycle repeats at 12-14 Hz (spindle frequency)
• K complex: Cortical "up state" (depolarization phase) + triggered sleep spindle

EEG Rhythms Reference:

• Occur during REM sleep
• Originate in cholinergic pons → lateral geniculate body → occipital cortex
• Associated with rapid eye movements; possibly drive visual dream imagery

PET Activity (Ganong's; Neuroscience: Exploring the Brain):

• REM sleep: ↑ Pons, amygdala, anterior cingulate, extrastriate visual cortex; ↓ prefrontal cortex, primary visual cortex, parietal cortex
• NREM sleep: Overall ↓ global glucose use

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20. Stages of NREM Sleep (N1, N2, N3)

Stage N1 - Light/Transitional Sleep

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Stage N2 - Intermediate Sleep

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Stage N3 - Slow-Wave Sleep (SWS/Deep Sleep)

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Summary Comparison:

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21. REM Sleep Physiology

EEG During REM:

• Low-amplitude, mixed-frequency (similar to active wakefulness) - "paradoxical" sleep
• Sawtooth waves: 2-6 Hz, notched triangular waves; appear just before bursts of rapid eye movements
• Beta/gamma activity; highly desynchronized
• PGO spikes: cholinergic pons → geniculate → occipital cortex

Eye Movements:

• Rapid, conjugate, binocular movements in clusters (REM bursts)
• Arise from activation of paramedian pontine reticular formation (PPRF) and superior colliculus

Muscle Atonia - Mechanism:

• SLD/Subceruleus neurons → medullary reticular formation → GABA + glycinergic interneurons → hyperpolarize spinal motor neurons → generalized skeletal muscle atonia
• NOT involving cardiac/smooth muscle/diaphragm (these are spared)
• Atonia purpose: prevents acting out dreams

Autonomic Activity During REM:

• Highly variable - phasic surges of sympathetic activity (causing variable HR, BP, respiratory rate)
• During tonic REM: reduced sympathetic tone similar to NREM
• During phasic REM (with eye movements): sympathetic surges → ↑ HR, ↑ BP, ↑ penile/clitoral tumescence
• Genital erections (nocturnal penile tumescence, NPT) occur in ALL sleep cycles of REM → useful clinically to distinguish psychogenic vs organic impotence

Respiratory Changes in REM:

• Breathing becomes irregular (unlike regular NREM)
• ↓ intercostal and accessory muscle activity (partially paralyzed with atonia)
• Most severe O2 desaturations in REM sleep (especially in OSA, COPD)
• CO2 responsiveness further reduced compared to NREM

Cardiovascular in REM:

• HR and BP are highly variable (phasic swings)
• Most myocardial infarctions and strokes occur early morning (highest REM density + post-arousal sympathetic surge)

Temperature:

• Poikilothermic (thermoregulation ceases during REM) - body temperature follows ambient temperature; sweating and shivering are suppressed

Brain Activity:

• Active brain regions: limbic system (amygdala), motor cortex, brainstem, extrastriate visual cortex
• Deactivated: prefrontal cortex (explains illogical, uncritical nature of dreams), primary visual cortex, dorsolateral prefrontal

REM in Neonates:

• Neonates spend ~50% of sleep in REM; enter REM directly from wakefulness
• Premature infants: ~80% REM
• Active sleep (REM equivalent) in neonates: myoclonic twitches, sucking, grimacing, irregular respiration

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22. Sleep Cycle Across the Night

Temporal Distribution:

Cycle Details:

• Each NREM-REM cycle: ~90 minutes
• 4-6 cycles per 8-hour night
• First REM period: ~10-15 minutes at ~90 min after sleep onset
• Last REM period: up to 45-60 minutes
• REM latency: Normal = 90 ± 30 minutes; <60 min = pathological (depression, narcolepsy)
• N3 latency: ~45 min from sleep onset

Sleep Structure Rules:

• Deepest sleep occurs early (protective; ensures restorative sleep even if interrupted)
• Arousal threshold: lowest in N1 and REM; highest in N3
• REM rebound: After REM deprivation → ↑ REM pressure → ↑ REM on subsequent nights
• SWS rebound: After total sleep deprivation → SWS rebounds first (prioritized); then REM

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23. Age-Related Changes in Sleep

Developmental Changes:

Aging-Specific Changes:

• N3 (SWS): Progressively declines with age; may be completely absent in elderly
• N1: Increases (more light, fragmented sleep)
• Sleep efficiency: Decreases (more WASO - wake after sleep onset)
• REM latency: May shorten
• Circadian phase: Advances (earlier bedtime, earlier wake time) → "morningness" in elderly
• Daytime napping: Increases to compensate for nocturnal deficits
• Sleep spindle density: Decreases with age
• Anatomical basis: Loss of VLPO neurons (especially galanin-expressing) with aging and in Alzheimer's disease

Neonatal Sleep Special Features:

• Enter REM directly from wakefulness (no initial NREM period)
• REM accompanied by: body twitches, sucking, grimacing, irregular breathing ("active sleep")
• Sleep spindles appear: ~3 months; K complexes: ~6 months
• Adult sleep cycle duration (~90 min) reached by ~age 10 years

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24. Respiratory Physiology During Sleep

Normal Respiratory Changes During Sleep:

Why Hypoventilation Occurs During Sleep:

1. Withdrawal of wakefulness drive (wakeful drive to breathe via ARAS) - the most important cause
2. Increased upper airway resistance (reduced pharyngeal muscle tone)
3. Reduced intercostal/accessory muscle activity
4. Positional effects (supine → diaphragm movement restricted)

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25. Ventilatory Control in Sleep

Chemoreceptor Sensitivity During Sleep:

Apnea Threshold:

• During NREM, a CO2 apnea threshold exists: if PaCO2 falls below this threshold (e.g., after hyperventilation), breathing stops (central apnea) until CO2 rises again
• The apnea threshold is ~2-4 mmHg below eupneic CO2 level during NREM
• The wakefulness drive eliminates this threshold during wakefulness (no apnea threshold awake)
• NREM central apneas (e.g., at high altitude, in heart failure = Cheyne-Stokes respiration) are partly explained by this mechanism

Respiratory Muscle Control During REM:

• Diaphragm: Relatively preserved (phrenic nerve drive intact)
• Intercostal muscles: Markedly reduced (participate in REM atonia)
• Upper airway dilators: Reduced → ↑ pharyngeal collapsibility → OSA worsens in REM
• This creates a "paradoxical" breathing pattern in REM (chest sinks while abdomen rises)

Upper Airway Reflexes:

• Subatmospheric pressure reflex: Negative pressure in pharynx → activates genioglossus and other dilators (awake)
• This reflex is markedly attenuated during sleep → contributes to OSA pathogenesis

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26. Upper Airway Physiology During Sleep

Pharyngeal Anatomy and Physiology:

• The pharynx is a collapsible tube surrounded by dilator muscles
• Genioglossus (hypoglossal nerve, CN XII) = most important pharyngeal dilator muscle
• Other dilators: tensor palatini, geniohyoid, palatoglossus

Changes During Sleep:

• Pharyngeal muscle tone is reduced in all sleep stages
• Greatest reduction in REM (atonia affects intercostals and accessory muscles; pharyngeal dilators partially affected)
• Upper airway resistance doubles in NREM; increases further in REM

Starling Resistor Model (OSA Pathophysiology):

• Pharynx behaves like a Starling resistor
• Pcrit (critical closing pressure): The pressure at which pharynx collapses
  • Healthy adults: Pcrit < -8 cmH2O (pharynx stays open even with large negative pressure)
  • OSA patients: Pcrit > 0 cmH2O (pharynx collapses under slight negative pressure)
  • Simple snorers: Pcrit between healthy and OSA

Factors Increasing Pcrit (worsening OSA):

• Obesity (fat deposition around pharynx)
• Supine posture (tongue falls back; retrognathia)
• Muscle relaxants, alcohol, sedatives
• NREM/REM sleep state
• Aging (reduced muscle tone)
• Anatomy (retrognathia, large tonsils, narrow palate)

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27. Gas Exchange During Sleep

PaO2 and PaCO2 Changes:

• PaO2 falls 3-10 mmHg compared to wakefulness (due to hypoventilation and ↑ V/Q mismatch)
• PaCO2 rises 2-8 mmHg
• SaO2 decreases 2-4%

• Further hypoventilation + intercostal atonia → more V/Q mismatch
• Greater drops in PaO2 and SaO2 (especially in pre-existing lung disease)
• Oxygen desaturations are worst and most prolonged during REM sleep in OSA and COPD

V/Q Mismatch During Sleep:

• Functional residual capacity (FRC) decreases in supine position → atelectasis in dependent lung zones → ↑ shunt
• This is most marked during REM due to intercostal atonia reducing chest wall tone

In Disease States:

• COPD: Normally at borderline PaO2; during sleep (especially REM) → drops into steep part of O2-Hb dissociation curve → severe desaturations
• OSA: Intermittent complete airway obstruction → recurrent hypoxia-reoxygenation cycles → oxidative stress, sympathetic activation
• Hypoventilation syndromes: Most hypoventilation occurs during REM

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28. Cardiovascular Physiology During Sleep

NREM Sleep - Cardiovascular Changes:

REM Sleep - Cardiovascular Changes:

Clinical Significance:

• Most acute MIs occur in the early morning (6 AM-12 PM): highest REM density + adrenergic surge on awakening
• Coronary artery spasm (Prinzmetal angina): Occurs during REM sleep
• Sudden cardiac death: Peak incidence 6 AM-12 PM
• Cardiac arrhythmias: ↑ during phasic REM (bradycardia-tachycardia swings)
• Nocturnal hypertension: Persistent high BP during sleep → end-organ damage

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29. Autonomic Nervous System Changes During Sleep

NREM Sleep:

• Parasympathetic dominant state
• ↓ Sympathetic nerve activity (measured by microneurography)
• ↓ Heart rate variability (HRV) → increased HF component (parasympathetic)
• ↓ Plasma norepinephrine, renin, aldosterone
• Regular respiration, regular HR
• Baroreflex sensitivity: Preserved/increased

REM Sleep:

• Increased sympathetic variability - phasic surges of sympathetic activity
• Tonic REM: similar low sympathetic tone to NREM
• Phasic REM (with REMs): ↑ sympathetic burst activity → ↑ HR, ↑ BP, pupil dilation, piloerection, adrenal secretion
• Thermoregulatory reflexes suspended (poikilothermia)
• Cardiac vagal tone: Reduced during phasic REM

Overall Night:

• Lowest sympathetic activity: first NREM cycle (SWS)
• Highest sympathetic activity: phasic REM periods (especially late-night REM)
• Plasma catecholamines are lowest during NREM; rise sharply at awakening

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30. Endocrine Physiology of Sleep

Growth Hormone (GH):

• Secreted in large pulsatile bursts during N3 (SWS)
• First N3 period contains the largest GH pulse of the 24-hour period
• Regulated by GHRH (stimulates GH release; also promotes SWS) and somatostatin
• Sleep deprivation → markedly ↓ GH secretion
• In children: ~70-90% of daily GH secreted during sleep (critical for growth)
• Adults: Smaller pulses; GH secretion during sleep declines with age (parallels N3 decline)

Cortisol:

• Follows circadian rhythm (NOT sleep-dependent)
• Lowest in first half of night (midnight - 2 AM)
• Rises in early morning hours → peaks at/just before awakening (~8 AM)
• ACTH secretion drives this pattern (entrainment by SCN → CRH pulsatility)
• Sleep deprivation → slightly elevated evening cortisol

Thyroid-Stimulating Hormone (TSH):

• Peak in late evening (just before sleep onset)
• Suppressed during sleep (sleep actively suppresses TSH)
• Sleep deprivation → TSH remains elevated throughout night

Prolactin:

• Secretion ↑ during sleep; peak at onset of sleep and continues through night
• Highest levels in early morning
• Sleep is the major stimulus for prolactin release (not light-dark cycle per se)

Melatonin:

• Released by pineal gland in darkness
• DLMO (dim-light melatonin onset): ~2-4 hours before habitual sleep onset
• Peaks 2-4 AM; very low during day
• Signals "night" to SCN and peripheral clocks

Leptin and Ghrelin:

• Leptin (satiety hormone): ↑ during sleep; sleep deprivation → ↓ leptin
• Ghrelin (hunger hormone): ↑ during sleep deprivation
• Short sleep → ↓ leptin + ↑ ghrelin → increased appetite → obesity risk

LH/FSH:

• In puberty: LH pulses occur predominantly during sleep (critical for pubertal development)
• In adults: LH pulses less sleep-dependent

Insulin and Glucose:

• Insulin sensitivity: Highest in morning (following morning cortisol peak); decreased during sleep especially in first half
• Glucose production: Reduced during SWS; ↑ during REM

Renin-Angiotensin-Aldosterone (RAAS):

• Renin: Oscillates with NREM-REM cycles (↑ during NREM, ↓ during REM)
• Aldosterone: Peaks during sleep

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31. Metabolic Physiology of Sleep

Basal Metabolic Rate (BMR):

• Falls 10-15% during NREM sleep (lowest during N3)
• Returns toward waking levels during REM
• Body temperature falls ~0.5-1°C during sleep (core body temperature)

Brain Metabolism:

• NREM: ↓ global cerebral blood flow (CBF) and glucose utilization; especially thalamus, basal ganglia, brainstem, anterior hypothalamus
• REM: ↑ CBF in limbic areas, pons, amygdala; ↓ in prefrontal cortex

Glucose Regulation:

• Sleep deprivation → glucose intolerance (↓ glucose disposal, ↑ counterregulatory hormones)
• Short sleep duration associated with: type 2 diabetes, metabolic syndrome, obesity
• Mechanism: ↑ cortisol, ↑ sympathetic activity, ↓ insulin sensitivity, ↑ ghrelin/↓ leptin

Energy Balance:

• Synaptic homeostasis: During wakefulness, widespread synaptic potentiation (LTP-like) → ↑ energy and space demand; during sleep, downscaling reduces energy consumption per synapse

Protein Synthesis:

• Genes for protein synthesis, cholesterol synthesis, and heme synthesis are upregulated during sleep → "Sleep prepares for subsequent wakefulness"

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32. Renal Physiology During Sleep

Urine Output:

• Decreases markedly during sleep (nocturnal oliguria)
• Normal adult: urine output ~0.5 mL/min awake; falls to ~0.25-0.3 mL/min during sleep

Mechanisms:

1. ADH (Vasopressin): Increases during sleep (peaks at night) → promotes water reabsorption
2. ↓ GFR: Falls during sleep due to ↓ renal blood flow (vasoconstriction) and ↓ cardiac output
3. ↓ Aldosterone-driven sodium excretion: Aldosterone ↑ → sodium retained → reduced urine volume
4. Atrial Natriuretic Peptide (ANP): Falls during supine sleep → ↓ natriuresis
5. Renin oscillates with NREM-REM cycles

Sodium and Potassium:

• Sodium reabsorption ↑ during sleep
• Potassium excretion follows circadian pattern (peaks in morning)

Clinical Significance:

• Nocturia: Common complaint in elderly; partly from loss of nocturnal ADH peak (circadian dysfunction), cardiac failure, OSA (↑ ANP from right heart stretch due to hypoxia → natriuresis)
• OSA-related nocturia: Intrathoracic pressure swings → ↑ right atrial stretch → ↑ ANP → salt and water diuresis during sleep

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33. Thermoregulation During Sleep

Core Body Temperature (CBT):

• Falls during sleep onset (the CBT drop is both a consequence and a trigger of sleep)
• Lowest point: 4-6 AM (nadir of circadian temperature rhythm)
• Drops ~0.5-1°C from daytime maximum

Mechanism of Sleep-Temperature Link:

• Warm bath effect: Peripheral vasodilation (hands and feet) → heat loss → CBT falls → promotes sleep
• Preoptic area (VLPO region) neurons are thermosensitive: warm temperatures in anterior hypothalamus activate VLPO → promote sleep
• Skin warming before sleep (warm blanket, warm bath) → promotes sleep onset

During NREM Sleep:

• Normal thermoregulatory responses maintained (sweating to heat; shivering to cold)
• Metabolic rate ↓ → heat production ↓ → CBT falls
• Active heat loss via peripheral vasodilation

During REM Sleep - Poikilothermia:

• Thermoregulatory responses are suspended during REM sleep
• No sweating, no shivering, no piloerection during REM
• Body temperature follows ambient temperature (poikilothermic)
• This is due to inhibition of hypothalamic thermoregulatory neurons during REM
• Risk: Sleeping in extreme temperatures → core temperature swings during REM

Circadian Component:

• The CBT circadian rhythm is independent of sleep
• CBT minimum (~4-6 AM) coincides with lowest alertness and worst performance
• CBT maximum (~6-8 PM) coincides with peak athletic performance and alertness

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34. Immune Function and Sleep

Sleep Enhances Immune Function:

1. NK cell activity: ↑ during sleep; one night of partial sleep deprivation → ↓ NK cell cytotoxicity by ~30%
2. T-cell function: Antigen-specific T-cell immune response enhanced by sleep; sleep deprivation → attenuated vaccine response (hepatitis B, influenza vaccines)
3. Cytokines: IL-1β and TNF-α are somnogens (promote sleep); peak levels during infection → sick-sleep behavior (fever + excessive sleep = adaptive response)
4. Antibody production: Sleep deprivation → ↓ antibody titers after vaccination

Bidirectional Relationship:

• Sleep promotes immunity (recovery from infection)
• Immune activation promotes sleep (via cytokine release):
  • IL-1β, TNF-α, IL-6 → increase NREM sleep and SWS
  • These cytokines act on hypothalamus (VLPO, MnPO)

Sleep Deprivation Effects on Immunity:

• One night partial deprivation: ↓ NK cells, altered T-cell subsets
• Chronic sleep restriction (6 hr/night × 1 week): Transcriptional changes suggesting accelerated aging
• Chronic sleep deprivation → ↑ CRP, ↑ IL-6 → chronic low-grade inflammation → cardiovascular disease risk

Fever and Sleep:

• IL-1β and TNF-α (fever mediators) are also the most potent endogenous sleep-promoting substances known
• Fever → ↑ NREM, ↑ SWS (adaptive for immune consolidation)
• Drugs blocking IL-1/TNF → reduce NREM sleep (confirming link)

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35. Glymphatic System and Brain Waste Clearance

Discovery:

• Described by Maiken Nedergaard and colleagues, 2013
• Named: "glymphatic system" (glial + lymphatic)

Mechanism:

1. CSF flows along para-arterial spaces (Virchow-Robin spaces) into brain parenchyma
2. CSF driven by arterial pulsations + astrocytic aquaporin-4 (AQP4) channels on astrocyte endfeet (which ensheath blood vessels)
3. Convective flow of CSF through brain parenchyma → sweeps interstitial fluid (ISF) and metabolic waste products toward para-venous spaces
4. ISF drains along para-venous spaces → into deep cervical lymphatics → systemic circulation

Sleep-Dependent Clearance:

• Glymphatic flow is dramatically increased during sleep (~2× faster during sleep vs wakefulness)
• Mechanism: During sleep → ↓ noradrenaline (NE from LC) → ↓ astrocyte volume → extracellular space expands by ~60% → facilitates convective flow
• Brain size during sleep: Slight increase in extracellular space (from ~14% to ~22% of brain volume)
• NE directly contracts astrocytes → reduces extracellular space during wakefulness

What is Cleared:

• Beta-amyloid (Aβ): Cleared 2× faster during sleep
• Tau protein
• Lactate, K⁺, glutamate, heat shock proteins
• Metabolic by-products of neuronal activity

Alzheimer's Disease Connection:

• Sleep deprivation → ↑ beta-amyloid accumulation in brain
• Even ONE night of sleep deprivation → measurable ↑ beta-amyloid on PET scan in humans (Shokri-Kojori et al., PNAS 2018)
• AQP4 knockout mice: impaired glymphatic clearance → ↑ Aβ accumulation
• VLPO neuron loss in Alzheimer's → poor sleep → impaired glymphatic function → more Aβ accumulation (vicious cycle)
• APOE4 (Alzheimer's risk gene) → impairs AQP4 channel function

Body Posture:

• Lateral (side-sleeping) position → most efficient glymphatic clearance (compared to supine or prone) in rodent studies
• Potentially explains why many mammals sleep curled on their sides

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36. Memory Consolidation and Synaptic Plasticity

Sleep's Role in Memory:

Stages and Memory Types:

Two-Stage Model (Hippocampal-Cortical Consolidation):

1. Encoding during wakefulness: Hippocampus rapidly encodes new information (high-capacity, temporary)
2. SWS consolidation: Sharp-wave ripples (SWRs) from hippocampus (during down-to-up state transitions) → coordinate with sleep spindles (from thalamus) and slow oscillations (from cortex) → transfer information to neocortex for long-term storage ("systems consolidation")
3. REM sleep: Further processing, emotional tagging, integration with existing schemas

Synaptic Homeostasis Theory (SHY; Tononi & Cirelli):

• Wakefulness: Learning → widespread synaptic potentiation (LTP-like) throughout cortex → increased synaptic strength, increased AMPA receptors, increased BDNF, Arc gene activation → high energy cost
• SWS: Slow oscillations → net synaptic downscaling (LTD-like) → removes weak/unimportant synapses → reduces metabolic demand, restores synaptic capacity for next day's learning
• Prediction: Sleep spindles = mechanism of synaptic downscaling
• Prediction: SWA (slow-wave activity) reflects the need for synaptic homeostasis

Evidence for Memory Role of Sleep:

• Performance on hidden rule tasks (e.g., number sequence patterns) improved only after sleep (not after equal time awake)
• Declarative memory consolidation: Hippocampal activity during SWS predicts next-day performance improvement
• Motor skill consolidation: Stage 2 (N2) spindle density correlates with overnight motor learning improvement
• REM deprivation impairs fear extinction memory

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37. Dream Physiology

When Do Dreams Occur?

• REM sleep: Vivid, narrative, emotionally intense, visually rich, often bizarre; reported in 80-95% of REM awakenings
• NREM sleep: Duller, more thought-like, fragmentary, less visual; reported in ~50% of NREM awakenings (especially N2)
• N3 dreams: Rare, very fragmentary; night terrors arise from N3 but are not dreams per se

Neuroanatomical Correlates of REM Dreaming (PET/fMRI):

• Active: Pons, amygdala (emotional content), anterior cingulate, extrastriate visual cortex, limbic areas, motor cortex
• Inactive: Dorsolateral prefrontal cortex (explains logical failures), primary visual cortex, parietal cortex

Theories of Dream Generation:

1. Activation-Synthesis Hypothesis (Hobson & McCarley, 1977):

• Pontine REM-on neurons randomly activate forebrain during REM (PGO spikes)
• Random activation of motor, sensory, emotional, memory circuits → the forebrain ("synthesizes") a narrative to make sense of random activation = dream
• Dreams are essentially random activation + cortical interpretation
• Explains bizarreness (random activation) + emotional content (limbic activation) + visual imagery (extrastriate activation)

2. Default Mode Network (DMN) Hypothesis (modern):

• Dreaming involves activation of the default mode network (medial prefrontal, posterior cingulate, hippocampal areas)
• DMN = self-referential, episodic, autobiographical processing network
• Dreaming = internally directed cognition utilizing episodic memory

3. Threat Simulation Theory (Revonsuo):

• Dreams simulate threatening scenarios → evolutionary function = practice threat responses
• Nightmares/fear in dreams = adaptive

Lucid Dreams:

• Dreamer aware they are dreaming while in REM
• Associated with reactivation of prefrontal cortex during REM (normally deactivated)
• Can be induced by electrical stimulation of frontal cortex (40 Hz gamma stimulation) during REM

Nightmares vs Night Terrors:

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38. Sleep Physiology in Respiratory Diseases

Obstructive Sleep Apnea (OSA):

• Definition: Repetitive episodes of complete (apnea) or partial (hypopnea) upper airway obstruction during sleep
• AHI (Apnea-Hypopnea Index): Mild = 5-15/hr; Moderate = 15-30/hr; Severe = >30/hr
• Pathophysiology: ↑ Pcrit + ↓ pharyngeal muscle tone + ↑ upper airway resistance → airway collapse
• Consequences: Cyclical hypoxia-reoxygenation → oxidative stress, sympathetic activation, endothelial dysfunction, cardiovascular risk (hypertension, AF, stroke, MI)
• Sleep architecture disturbance: ↑ N1 (30-50%), ↓ N3, ↓ REM → excessive daytime sleepiness
• Worst in REM sleep (most muscle atonia; lowest arousal threshold)
• Associated with: male sex, obesity, large neck circumference, retrognathia, alcohol use

COPD and Sleep:

• COPD patients have:
  • ↓ Total sleep time; fragmented sleep; ↑ arousals
  • Oxygen desaturation during sleep (especially REM): most severe
  • Hypercapnia during REM (due to further hypoventilation + atonic intercostals)
  • Loss of normal circadian BP dipping
• REM hypoventilation: Main cause of nocturnal desaturation in COPD (especially those with daytime PaO2 near 60 mmHg)

Overlap Syndrome (OSA + COPD):

• Coined by Flenley (1985)
• Worse oxygen desaturation than either alone
• Higher risk of pulmonary hypertension, right heart failure, hypercapnia
• Requires CPAP + supplemental O2 or BiPAP

Asthma and Sleep:

• Asthma classically worse at 3-4 AM ("the morning dip"): lowest cortisol, ↑ parasympathetic tone → bronchoconstriction, ↑ airway inflammation, ↑ histamine
• Circadian variation in airway resistance: maximal around 4 AM
• Sleep deprivation → ↑ asthma symptoms

Obesity Hypoventilation Syndrome (OHS):

• BMI >30 + daytime hypercapnia (PaCO2 >45 mmHg) + no other cause
• Hypoventilation worst during REM sleep
• Associated OSA in ~90% of cases

Central Sleep Apnea (CSA) and Cheyne-Stokes Respiration:

• Cheyne-Stokes: Waxing-waning respirations with central apneas; seen in heart failure, stroke
• Mechanism: ↑ loop gain in ventilatory control + below-apnea threshold PaCO2 drop during hyperventilation phase → central apnea
• Treated with: CPAP, ASV (Adaptive Servo-Ventilation)

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39. Recent Advances in Sleep Physiology

1. Orexin Receptor Antagonists (Dual Orexin Receptor Antagonists - DORAs):

• Suvorexant (Belsomra) - FDA approved 2014: Blocks both OX1R and OX2R → promotes sleep without CNS depression (unlike benzodiazepines/barbiturates)
• Lemborexant (Dayvigo) - FDA approved 2019: Higher affinity, more rapid OX2R on/off kinetics
• Daridorexant (Quviviq) - FDA approved 2022: Less next-morning sedation
• Mechanism: Removing orexin's wake-stabilizing effect → sleep without suppressing REM or SWS (key advantage over older agents)

2. Glymphatic System Advances:

• Nedergaard et al. 2013: Original discovery of glymphatic system
• 2017-2023: Demonstrated in humans using MRI/PET techniques
• AQP4 channels on astrocyte endfeet required for efficiency
• Sleep posture studies: Lateral position most efficient (rodent data)
• Even one night of sleep deprivation → ↑ tau and Aβ in CSF (multiple recent human studies)

3. Neuroimaging Advances:

• High-density EEG + MRI: Identified brain regions entering local sleep even during wakefulness (sleep deprivation → sleep intrusions into wakefulness)
• fMRI during natural sleep: Difficult but achievable with ultra-fast protocols
• Sleep slow waves traveling across the cortex like "waves on a beach" (not simultaneous) - Massimini et al.

4. Synaptic Homeostasis Evidence:

• Direct evidence that SWA (slow-wave activity) reflects net synaptic potentiation during prior wakefulness
• GluA1 (AMPA receptor subunit) density highest at end of wakefulness; falls after sleep
• Sleep spindles and K complexes: Now understood as mechanisms of synaptic downscaling

5. Molecular Clock Advances:

• Clock genes now identified in virtually every human tissue
• Chrono-pharmacology: Drug timing optimized based on circadian gene expression (cancer chemotherapy timing, cardiovascular drug timing, antibiotic timing)
• Melatonin receptor agonists (ramelteon, tasimelteon) for circadian disorders
• Tasimelteon (Hetlioz): FDA approved for non-24-hour sleep-wake disorder in blind patients (MT1/MT2 agonist)

6. Adenosine and Caffeine Mechanistic Studies:

• A2a receptor knockout mice: Do not respond to adenosine accumulation → less sleep pressure
• Identified nucleus accumbens shell as key A2a-expressing node linking adenosine → VLPO activation
• Opened possibility of A2a antagonists as safer wakefulness promoters

7. Microbiome-Sleep Axis:

• Gut microbiome produces muramyl peptide and other somnogens
• Gut bacteria metabolites influence tryptophan → serotonin → melatonin pathway
• Dysbiosis associated with insomnia and poor sleep quality

8. Sex Differences in Sleep:

• Women spend more time in N3 (SWS) than men of same age
• Women have greater sleep spindle density
• Women less susceptible to total sleep deprivation effects (on some cognitive tasks)
• Hormonal effects: Insomnia worsens at menopause (loss of estrogen/progesterone → ↓ sleep quality)
• Progesterone: Mild respiratory stimulant → protective against OSA in premenopausal women

9. COVID-19 and Sleep:

• Post-COVID insomnia ("COVID somnia") highly prevalent
• Neuroinvasion of SARS-CoV-2 → affects hypothalamic sleep centers, brainstem, basal forebrain
• Long-COVID fatigue associated with dysregulation of glymphatic system and immune activation

10. NREM Parasomnias - Neurophysiology:

• Local sleep / "sleep inertia" hypothesis: Parasomnias arise from coexistence of local wakefulness (in motor cortex, basal forebrain) and local sleep (in frontal cortex) simultaneously
• Supports the concept that sleep and wakefulness are not global states but can exist locally in different brain regions

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SLEEP PHYSIOLOGY — TOPICS WITH REFERENCES

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Guyton and Hall Textbook of Medical Physiology - Hall JE, Hall ME. 14th ed. Elsevier, 2021. Chapter 60. Harrison's Principles of Internal Medicine - Kasper DL et al. 22nd ed. McGraw-Hill, 2022. Chapter 31. Neuroscience: Exploring the Brain - Bear MF, Connors BW, Paradiso MA. 5th ed. Jones & Bartlett, 2020. Chapter 19.

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Guyton and Hall Textbook of Medical Physiology - Hall JE, Hall ME. 14th ed. Elsevier, 2021. Chapter 60. Ganong's Review of Medical Physiology - Barrett KE et al. 26th ed. McGraw-Hill, 2019. Chapter 14. Neuroscience: Exploring the Brain - Bear MF, Connors BW, Paradiso MA. 5th ed. Jones & Bartlett, 2020. Chapter 19 (Table 19.1).

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Guyton and Hall Textbook of Medical Physiology - Hall JE, Hall ME. 14th ed. Elsevier, 2021. Chapter 60. Principles of Neural Science - Kandel ER et al. 6th ed. McGraw-Hill, 2021. Chapter 51. Neuroscience: Exploring the Brain - Bear MF, Connors BW, Paradiso MA. 5th ed. Jones & Bartlett, 2020. Chapter 19. Fishman's Pulmonary Diseases and Disorders - Grippi MA et al. 5th ed. McGraw-Hill, 2015. Chapter 112.

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Guyton and Hall Textbook of Medical Physiology - Hall JE, Hall ME. 14th ed. Elsevier, 2021. Chapter 60. Adams and Victor's Principles of Neurology - Ropper AH, Samuels MA, Klein JP. 12th ed. McGraw-Hill, 2023. Chapter 19. Principles of Neural Science - Kandel ER et al. 6th ed. McGraw-Hill, 2021. Chapter 51.

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Harrison's Principles of Internal Medicine - Kasper DL et al. 22nd ed. McGraw-Hill, 2022. Chapter 31. Ganong's Review of Medical Physiology - Barrett KE et al. 26th ed. McGraw-Hill, 2019. Chapter 14. Bradley and Daroff's Neurology in Clinical Practice - Daroff RB et al. 8th ed. Elsevier, 2022. Chapter 101.

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Kaplan and Sadock's Comprehensive Textbook of Psychiatry - Sadock BJ, Sadock VA, Ruiz P. 10th ed. Wolters Kluwer, 2017. Chapter 1.7 (Chronobiology). Harrison's Principles of Internal Medicine - Kasper DL et al. 22nd ed. McGraw-Hill, 2022. Chapter 31. Adams and Victor's Principles of Neurology - Ropper AH et al. 12th ed. McGraw-Hill, 2023. Chapter 19. Principles of Neural Science - Kandel ER et al. 6th ed. McGraw-Hill, 2021. Chapter 51.

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Harrison's Principles of Internal Medicine - Kasper DL et al. 22nd ed. McGraw-Hill, 2022. Chapter 31. Principles of Neural Science - Kandel ER et al. 6th ed. McGraw-Hill, 2021. Chapter 51. Kaplan and Sadock's Comprehensive Textbook of Psychiatry - Sadock BJ et al. 10th ed. Wolters Kluwer, 2017. Stahl's Essential Psychopharmacology - Stahl SM. 5th ed. Cambridge University Press, 2021. Chapter 11.

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Kaplan and Sadock's Comprehensive Textbook of Psychiatry - Sadock BJ et al. 10th ed. Wolters Kluwer, 2017. Chapter 1.7. Bradley and Daroff's Neurology in Clinical Practice - Daroff RB et al. 8th ed. Elsevier, 2022. Chapter 5. Harrison's Principles of Internal Medicine - Kasper DL et al. 22nd ed. McGraw-Hill, 2022. Chapter 31. Localization in Clinical Neurology - Brazis PW, Masdeu JC, Biller J. 8th ed. Lippincott Williams & Wilkins, 2022.

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Principles of Neural Science - Kandel ER et al. 6th ed. McGraw-Hill, 2021. Chapter 51. Adams and Victor's Principles of Neurology - Ropper AH et al. 12th ed. McGraw-Hill, 2023. Chapter 19. Fishman's Pulmonary Diseases and Disorders - Grippi MA et al. 5th ed. McGraw-Hill, 2015. Chapter 112. Harrison's Principles of Internal Medicine - Kasper DL et al. 22nd ed. McGraw-Hill, 2022. Chapter 31.

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Kaplan and Sadock's Comprehensive Textbook of Psychiatry - Sadock BJ et al. 10th ed. Wolters Kluwer, 2017. Neuroscience: Exploring the Brain - Bear MF, Connors BW, Paradiso MA. 5th ed. Jones & Bartlett, 2020. Chapter 19. Stahl's Essential Psychopharmacology - Stahl SM. 5th ed. Cambridge University Press, 2021. Chapter 11.

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Bradley and Daroff's Neurology in Clinical Practice - Daroff RB et al. 8th ed. Elsevier, 2022. Chapter 101, Table 101. Kaplan and Sadock's Comprehensive Textbook of Psychiatry - Sadock BJ et al. 10th ed. Wolters Kluwer, 2017. Ganong's Review of Medical Physiology - Barrett KE et al. 26th ed. McGraw-Hill, 2019. Chapter 14. Stahl's Essential Psychopharmacology - Stahl SM. 5th ed. Cambridge University Press, 2021. Chapter 11.

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Stahl's Essential Psychopharmacology - Stahl SM. 5th ed. Cambridge University Press, 2021. Chapter 11. Neuroscience: Exploring the Brain - Bear MF, Connors BW, Paradiso MA. 5th ed. Jones & Bartlett, 2020. Chapter 19. Kaplan and Sadock's Comprehensive Textbook of Psychiatry - Sadock BJ et al. 10th ed. Wolters Kluwer, 2017. Harrison's Principles of Internal Medicine - Kasper DL et al. 22nd ed. McGraw-Hill, 2022. Chapter 31.

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Principles of Neural Science - Kandel ER et al. 6th ed. McGraw-Hill, 2021. Chapter 51. Harrison's Principles of Internal Medicine - Kasper DL et al. 22nd ed. McGraw-Hill, 2022. Chapter 31. Adams and Victor's Principles of Neurology - Ropper AH et al. 12th ed. McGraw-Hill, 2023. Chapter 19. Fishman's Pulmonary Diseases and Disorders - Grippi MA et al. 5th ed. McGraw-Hill, 2015. Chapter 112. Neuroscience: Exploring the Brain - Bear MF, Connors BW, Paradiso MA. 5th ed. Jones & Bartlett, 2020. Chapter 19.

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Principles of Neural Science - Kandel ER et al. 6th ed. McGraw-Hill, 2021. Chapter 51. Harrison's Principles of Internal Medicine - Kasper DL et al. 22nd ed. McGraw-Hill, 2022. Chapter 31. Kaplan and Sadock's Comprehensive Textbook of Psychiatry - Sadock BJ et al. 10th ed. Wolters Kluwer, 2017. Stahl's Essential Psychopharmacology - Stahl SM. 5th ed. Cambridge University Press, 2021. Chapter 11. Borbély AA. A two process model of sleep regulation. Hum Neurobiol. 1982;1(3):195-204.

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Principles of Neural Science - Kandel ER et al. 6th ed. McGraw-Hill, 2021. Chapter 51. Kaplan and Sadock's Comprehensive Textbook of Psychiatry - Sadock BJ et al. 10th ed. Wolters Kluwer, 2017. Ganong's Review of Medical Physiology - Barrett KE et al. 26th ed. McGraw-Hill, 2019. Chapter 14. Guyton and Hall Textbook of Medical Physiology - Hall JE, Hall ME. 14th ed. Elsevier, 2021. Chapter 60. Neuroscience: Exploring the Brain - Bear MF, Connors BW, Paradiso MA. 5th ed. Jones & Bartlett, 2020. Chapter 17.

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Neuroscience: Exploring the Brain - Bear MF, Connors BW, Paradiso MA. 5th ed. Jones & Bartlett, 2020. Chapter 17. Principles of Neural Science - Kandel ER et al. 6th ed. McGraw-Hill, 2021. Chapter 51. Harrison's Principles of Internal Medicine - Kasper DL et al. 22nd ed. McGraw-Hill, 2022. Chapter 31. Hall JC, Rosbash M, Young MW. Nobel Lecture, 2017. [Nobel Prize in Physiology or Medicine 2017] Katzenberg D et al. A CLOCK polymorphism associated with human diurnal preference. Sleep. 1998;21(6):569-576.

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Bradley and Daroff's Neurology in Clinical Practice - Daroff RB et al. 8th ed. Elsevier, 2022. Chapter 101. Harrison's Principles of Internal Medicine - Kasper DL et al. 22nd ed. McGraw-Hill, 2022. Chapter 31. Ganong's Review of Medical Physiology - Barrett KE et al. 26th ed. McGraw-Hill, 2019. Chapter 14. Neuroscience: Exploring the Brain - Bear MF, Connors BW, Paradiso MA. 5th ed. Jones & Bartlett, 2020. Chapter 19.

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Bradley and Daroff's Neurology in Clinical Practice - Daroff RB et al. 8th ed. Elsevier, 2022. Chapter 101. Harrison's Principles of Internal Medicine - Kasper DL et al. 22nd ed. McGraw-Hill, 2022. Chapter 31. Ganong's Review of Medical Physiology - Barrett KE et al. 26th ed. McGraw-Hill, 2019. Chapter 14. Neuroscience: Exploring the Brain - Bear MF, Connors BW, Paradiso MA. 5th ed. Jones & Bartlett, 2020. Chapter 19.

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Guyton and Hall Textbook of Medical Physiology - Hall JE, Hall ME. 14th ed. Elsevier, 2021. Chapter 60. Ganong's Review of Medical Physiology - Barrett KE et al. 26th ed. McGraw-Hill, 2019. Chapter 14. Neuroscience: Exploring the Brain - Bear MF, Connors BW, Paradiso MA. 5th ed. Jones & Bartlett, 2020. Chapter 19. Bradley and Daroff's Neurology in Clinical Practice - Daroff RB et al. 8th ed. Elsevier, 2022. Chapter 34. Principles of Neural Science - Kandel ER et al. 6th ed. McGraw-Hill, 2021. Chapter 51.

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Bradley and Daroff's Neurology in Clinical Practice - Daroff RB et al. 8th ed. Elsevier, 2022. Chapter 101. Ganong's Review of Medical Physiology - Barrett KE et al. 26th ed. McGraw-Hill, 2019. Chapter 14. Neuroscience: Exploring the Brain - Bear MF, Connors BW, Paradiso MA. 5th ed. Jones & Bartlett, 2020. Chapter 19. Guyton and Hall Textbook of Medical Physiology - Hall JE, Hall ME. 14th ed. Elsevier, 2021. Chapter 60. Harrison's Principles of Internal Medicine - Kasper DL et al. 22nd ed. McGraw-Hill, 2022. Chapter 31. Berry RB et al. AASM Manual for the Scoring of Sleep and Associated Events. Version 2.6. American Academy of Sleep Medicine, 2020.

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Principles of Neural Science - Kandel ER et al. 6th ed. McGraw-Hill, 2021. Chapter 51. Ganong's Review of Medical Physiology - Barrett KE et al. 26th ed. McGraw-Hill, 2019. Chapter 14. Harrison's Principles of Internal Medicine - Kasper DL et al. 22nd ed. McGraw-Hill, 2022. Chapter 31. Neuroscience: Exploring the Brain - Bear MF, Connors BW, Paradiso MA. 5th ed. Jones & Bartlett, 2020. Chapter 19. Aserinsky E, Kleitman N. Regularly occurring periods of eye motility, and concomitant phenomena, during sleep. Science. 1953;118(3062):273-274.

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Bradley and Daroff's Neurology in Clinical Practice - Daroff RB et al. 8th ed. Elsevier, 2022. Chapter 101. Harrison's Principles of Internal Medicine - Kasper DL et al. 22nd ed. McGraw-Hill, 2022. Chapter 31. Ganong's Review of Medical Physiology - Barrett KE et al. 26th ed. McGraw-Hill, 2019. Chapter 14. Guyton and Hall Textbook of Medical Physiology - Hall JE, Hall ME. 14th ed. Elsevier, 2021. Chapter 60.

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Harrison's Principles of Internal Medicine - Kasper DL et al. 22nd ed. McGraw-Hill, 2022. Chapter 31. Bradley and Daroff's Neurology in Clinical Practice - Daroff RB et al. 8th ed. Elsevier, 2022. Chapter 101. Principles of Neural Science - Kandel ER et al. 6th ed. McGraw-Hill, 2021. Chapter 51. Kaplan and Sadock's Comprehensive Textbook of Psychiatry - Sadock BJ et al. 10th ed. Wolters Kluwer, 2017.

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Fishman's Pulmonary Diseases and Disorders - Grippi MA et al. 5th ed. McGraw-Hill, 2015. Chapter 112. Harrison's Principles of Internal Medicine - Kasper DL et al. 22nd ed. McGraw-Hill, 2022. Chapter 31. Murray and Nadel's Textbook of Respiratory Medicine - Broaddus VC et al. 7th ed. Elsevier, 2022. Chapter 108. Ganong's Review of Medical Physiology - Barrett KE et al. 26th ed. McGraw-Hill, 2019. Chapter 34.

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Fishman's Pulmonary Diseases and Disorders - Grippi MA et al. 5th ed. McGraw-Hill, 2015. Chapter 112. Murray and Nadel's Textbook of Respiratory Medicine - Broaddus VC et al. 7th ed. Elsevier, 2022. Chapter 108. Harrison's Principles of Internal Medicine - Kasper DL et al. 22nd ed. McGraw-Hill, 2022. Chapter 31. Ganong's Review of Medical Physiology - Barrett KE et al. 26th ed. McGraw-Hill, 2019. Chapter 34.

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Fishman's Pulmonary Diseases and Disorders - Grippi MA et al. 5th ed. McGraw-Hill, 2015. Chapter 112-113. Murray and Nadel's Textbook of Respiratory Medicine - Broaddus VC et al. 7th ed. Elsevier, 2022. Chapter 108. Harrison's Principles of Internal Medicine - Kasper DL et al. 22nd ed. McGraw-Hill, 2022. Chapters 31, 294. Schwartz AR et al. Pharyngeal critical closing pressure (Pcrit) in the evaluation of sleep-disordered breathing. Sleep. 1995;18(10):769-779.

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Fishman's Pulmonary Diseases and Disorders - Grippi MA et al. 5th ed. McGraw-Hill, 2015. Chapter 112. Murray and Nadel's Textbook of Respiratory Medicine - Broaddus VC et al. 7th ed. Elsevier, 2022. Chapter 108. Ganong's Review of Medical Physiology - Barrett KE et al. 26th ed. McGraw-Hill, 2019. Chapter 34.

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Harrison's Principles of Internal Medicine - Kasper DL et al. 22nd ed. McGraw-Hill, 2022. Chapter 31. Fishman's Pulmonary Diseases and Disorders - Grippi MA et al. 5th ed. McGraw-Hill, 2015. Chapter 112. Braunwald's Heart Disease - Libby P et al. 12th ed. Elsevier, 2022. Chapter 89. Ganong's Review of Medical Physiology - Barrett KE et al. 26th ed. McGraw-Hill, 2019. Chapter 14.

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Harrison's Principles of Internal Medicine - Kasper DL et al. 22nd ed. McGraw-Hill, 2022. Chapter 31. Principles of Neural Science - Kandel ER et al. 6th ed. McGraw-Hill, 2021. Chapter 51. Ganong's Review of Medical Physiology - Barrett KE et al. 26th ed. McGraw-Hill, 2019. Chapter 14. Bradley and Daroff's Neurology in Clinical Practice - Daroff RB et al. 8th ed. Elsevier, 2022. Chapter 101.

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Harrison's Principles of Internal Medicine - Kasper DL et al. 22nd ed. McGraw-Hill, 2022. Chapters 31, 379. Ganong's Review of Medical Physiology - Barrett KE et al. 26th ed. McGraw-Hill, 2019. Chapters 14, 18. Guyton and Hall Textbook of Medical Physiology - Hall JE, Hall ME. 14th ed. Elsevier, 2021. Chapters 60, 76. Williams Textbook of Endocrinology - Melmed S et al. 14th ed. Elsevier, 2020. Chapter 7 (GH). Van Cauter E et al. Sleep and the endocrine system. Curr Opin Endocrinol Diabetes Obes. 2005.

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Harrison's Principles of Internal Medicine - Kasper DL et al. 22nd ed. McGraw-Hill, 2022. Chapter 31. Ganong's Review of Medical Physiology - Barrett KE et al. 26th ed. McGraw-Hill, 2019. Chapter 14. Guyton and Hall Textbook of Medical Physiology - Hall JE, Hall ME. 14th ed. Elsevier, 2021. Chapter 60. Spiegel K, Tasali E, Penev P, Van Cauter E. Brief communication: sleep curtailment in healthy young men is associated with decreased leptin levels, elevated ghrelin levels, and increased hunger and appetite. Ann Intern Med. 2004;141(11):846-850.

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Ganong's Review of Medical Physiology - Barrett KE et al. 26th ed. McGraw-Hill, 2019. Chapters 14, 37. Guyton and Hall Textbook of Medical Physiology - Hall JE, Hall ME. 14th ed. Elsevier, 2021. Chapters 60, 29. Harrison's Principles of Internal Medicine - Kasper DL et al. 22nd ed. McGraw-Hill, 2022. Chapter 31. Brenner and Rector's The Kidney - Yu ASL et al. 11th ed. Elsevier, 2020. Chapter 10.

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Guyton and Hall Textbook of Medical Physiology - Hall JE, Hall ME. 14th ed. Elsevier, 2021. Chapters 60, 74. Ganong's Review of Medical Physiology - Barrett KE et al. 26th ed. McGraw-Hill, 2019. Chapter 14. Principles of Neural Science - Kandel ER et al. 6th ed. McGraw-Hill, 2021. Chapter 51. Harrison's Principles of Internal Medicine - Kasper DL et al. 22nd ed. McGraw-Hill, 2022. Chapter 31. Czeisler CA, Buxton OM. The human circadian timing system and sleep-wake regulation. In: Principles and Practice of Sleep Medicine. Kryger M, Roth T, Dement WC. 6th ed. Elsevier, 2017.

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Harrison's Principles of Internal Medicine - Kasper DL et al. 22nd ed. McGraw-Hill, 2022. Chapter 31. Principles of Neural Science - Kandel ER et al. 6th ed. McGraw-Hill, 2021. Chapter 51. Neuroscience: Exploring the Brain - Bear MF, Connors BW, Paradiso MA. 5th ed. Jones & Bartlett, 2020. Chapter 19. Besedovsky L, Lange T, Born J. Sleep and immune function. Pflugers Arch. 2012;463(1):121-137. Irwin MR. Why sleep is important for health: a psychoneuroimmunology perspective. Annu Rev Psychol. 2015;66:143-172.

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Principles of Neural Science - Kandel ER et al. 6th ed. McGraw-Hill, 2021. Chapter 51. Neuroscience: Exploring the Brain - Bear MF, Connors BW, Paradiso MA. 5th ed. Jones & Bartlett, 2020. Chapter 19. Xie L et al. Sleep drives metabolite clearance from the adult brain. Science. 2013;342(6156):373-377. [PMID: 24136970] Shokri-Kojori E et al. β-Amyloid accumulation in the human brain after one night of sleep deprivation. Proc Natl Acad Sci USA. 2018;115(17):4483-4488. [PMID: 29632177] Iliff JJ et al. A paravascular pathway facilitates CSF flow through the brain parenchyma. Sci Transl Med. 2012;4(147):147ra111.

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Principles of Neural Science - Kandel ER et al. 6th ed. McGraw-Hill, 2021. Chapters 51, 65. Neuroscience: Exploring the Brain - Bear MF, Connors BW, Paradiso MA. 5th ed. Jones & Bartlett, 2020. Chapters 19, 24. Harrison's Principles of Internal Medicine - Kasper DL et al. 22nd ed. McGraw-Hill, 2022. Chapter 31. Tononi G, Cirelli C. Sleep and the price of plasticity: from synaptic and cellular homeostasis to memory consolidation and integration. Neuron. 2014;81(1):12-34. [PMID: 24411729] Born J, Wilhelm I. System consolidation of memory during sleep. Psychol Res. 2012;76(2):192-203.

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Principles of Neural Science - Kandel ER et al. 6th ed. McGraw-Hill, 2021. Chapter 51. Ganong's Review of Medical Physiology - Barrett KE et al. 26th ed. McGraw-Hill, 2019. Chapter 14. Kaplan and Sadock's Comprehensive Textbook of Psychiatry - Sadock BJ et al. 10th ed. Wolters Kluwer, 2017. Neuroscience: Exploring the Brain - Bear MF, Connors BW, Paradiso MA. 5th ed. Jones & Bartlett, 2020. Chapter 19. Hobson JA, McCarley RW. The brain as a dream state generator: an activation-synthesis hypothesis of the dream process. Am J Psychiatry. 1977;134(12):1335-1348. [PMID: 21570]

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Fishman's Pulmonary Diseases and Disorders - Grippi MA et al. 5th ed. McGraw-Hill, 2015. Chapters 112-115. Murray and Nadel's Textbook of Respiratory Medicine - Broaddus VC et al. 7th ed. Elsevier, 2022. Chapters 108-110. Harrison's Principles of Internal Medicine - Kasper DL et al. 22nd ed. McGraw-Hill, 2022. Chapters 31, 294. Principles and Practice of Sleep Medicine - Kryger M, Roth T, Dement WC. 6th ed. Elsevier, 2017. Sections on SDB, COPD, OSA. Flenley DC. Sleep in chronic obstructive lung disease. Clin Chest Med. 1985;6(4):651-661. [Overlap Syndrome - original paper]

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Principles of Neural Science - Kandel ER et al. 6th ed. McGraw-Hill, 2021. Chapter 51. Harrison's Principles of Internal Medicine - Kasper DL et al. 22nd ed. McGraw-Hill, 2022. Chapter 31. Michelson D et al. Suvorexant for the treatment of insomnia. N Engl J Med. 2014. Nedergaard M. Garbage truck of the brain. Science. 2013;340(6140):1529-1530. Xie L et al. Sleep drives metabolite clearance from the adult brain. Science. 2013;342(6156):373-377. [PMID: 24136970] Tononi G, Cirelli C. Sleep and the price of plasticity. Neuron. 2014;81(1):12-34. [PMID: 24411729] Mahler SV, Aston-Jones G. CNS states and the orexin system. Trends Neurosci. 2020. Varga AW et al. Sleep contributes to physical and mental health - a review of recent advances. J Clin Sleep Med. 2022.

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Master Reference List - Core Textbooks: