NEUROLOGY OF SLEEP DISORDERS

Abstract

A. Sleep: characterized by the complex interplay of physiologic and behavioral factorsB. Behavioral Definition of Sleep: a reversible physiologic state of decreased perception of and responsiveness to external stimuliA. No Single Accepted ModelB. Several Proposed Theories 1. Body repair 2. Brain restoration 3. Thermoregulation and energy conservation 4. Maintenance of immunocompetence 5. Memory consolidation and learning 6. UnlearningA. Animal Experiments 1. Total sleep deprivation in rats resulted in death ofunclear cause after a mean of 21 days a. Proposed mechanism: bacteremia, sepsis b. High metabolic rate, weight loss, decreased bodytemperature, and ulcerative skin lesions on tail and extremities preceded death2. Partial sleep deprivation: similar changes but slower rate of progression (death occurred after a mean of 37 days)3. Recovery sleep resulted in survivalB. Human Experiments 1. Most normal adults need 7.5 to 8 hours of nocturnal sleep2. Total sleep deprivation of 5 to 10 days: development of tremor, ptosis, diminished corneal reflex, hyperreflexia, nystagmus a. Electroencephalography (EEG): increased theta anddelta frequencies while awake with eyes closed and diminished alpha activityb. During recovery sleep: large amounts of slow wave sleep (SWS), i.e., SWS rebound, occur during first night; large amounts of rapid eye movement (REM) sleep occur during second night3. Partial sleep deprivation of 2 hours or more per night: impaired psychomotor function, mood changes, increased risk of falling asleep while driving, motor vehicle accidents a. Chronic partial sleep deprivation (4-6 hours nocturnalsleep) for 2 weeks: cumulative deficits on objective cognitive testingb. Recent studies on sleep-deprived medical and surgical residents showed increased medical errors: impairment of electrocardiogram interpretation, longer time to complete procedures, surgical errors, increased complication ratec. Sleep-deprived residents also showed deterioration of performance on psychomotor testing, increased risk of falling asleep while driving, increased number of traffic citations and accidentsd. Selective REM sleep deprivation leads to REM rebound during recovery sleep4. Subjective sleepiness increases with acute sleep loss but does not worsen significantly further with persistent sleep deprivationA. Sleep-Wakefulness Control Mechanisms: exerted by specific neuronal groups of brainstem ascending reticular activating system (ARAS) (Table 19-1)1. Pedunculopontine nucleus (cholinergic) 2. Laterodorsal tegmental nuclei (cholinergic) 3. Locus ceruleus (noradrenergic) 4. Raphe nuclei (serotonergic)B. ARAS: projects to intralaminar thalamic nuclei, posterior hypothalamus, basal forebrainC. Additional Neurotransmitters Involved in SleepWake Regulation1. Histamine (tuberomamillary nucleus): promotes arousal and wakefulness2. Dopamine (ventral tegmental area): promotes wakefulness3. Hypocretin (dorsolateral hypothalamus): promotes arousal4. Other sleep-promoting neurochemicals: γ-aminobutyric acid (GABA) (ventrolateral preoptic area), galanin, adenosine, cytokines (interleukins, C-reactive protein, tumor necrosis factor α), prostaglandin D2, delta sleep-inducing peptide, muramyl peptides, growth hormone-releasing factor, cortistatin, opioid peptidesD. Sleep Stages: non-rapid eye movement (NREM) sleep and REM sleep1. Normal sleep a. 4-6 cycles per night of NREM sleep, followed by REMsleep b. Cycle duration: about 90 minutes c. NREM sleep consists of stages I, II, III, and IV d. NREM sleep gets progressively deeper and arousalthreshold increases from stage I to IV e. Stage I is typically followed sequentially by stages II, III,and IV (stages III and IV = SWS) and again stage II before REM sleepf. Throughout the night1) SWS periods shorten 2) REM sleep periods lengthen 3) Thus, most NREM sleep occurs during first half ofthe night, followed by predominantly REM sleep in the second half2. Typical sleep architecture in a young adult (Fig. 19-1) a. Stage I: <5% b. Stage II: 40% to 60% c. Stage III/IV (SWS): 10% to 20% d. REM sleep: 20% to 25%E. NREM Sleep: general characteristics 1. Synchronized, rhythmic EEG activity 2. Decreased cerebral blood flow 3. Decreased skeletal muscle tone 4. Decreased heart rate, blood pressure, respiratory tidalvolumeF. Stage I 1. Dropout of occipital alpha rhythm 2. Low-amplitude theta activity 3. Positive occipital sharp transients of sleep (POSTS) 4. Vertex waves (V waves) over frontocentral leads 5. Slow rolling eye movements (horizontal) 6. Partial relaxation of voluntary musclesG. Stage II (Fig. 19-2) 1. K complexes: central high-amplitude, diphasic waves,>0.5 second in duration 2. Sleep spindles: central 12 to 14-Hz activity of 0.5 to 2seconds’ duration 3. POSTS, V waves, slow rolling eye movements mayoccasionally persistH. Stage III: synchronized, high-amplitude delta activity (≤2 Hz, ≥75 μV, 20%-50% of a 30-second epoch)Sleep is a physiologic state, and deprivation leads to derangements of cognitive and psychomotor function.