Chapter 028. Sleep Disorders (Part 1)

Harrisons Internal Medicine Chapter 28. Sleep DisordersSleep Disorders: Introduction Disturbed sleep is among the most frequent health complaints physicians encounter. More than one-half of adults in the United States experience at least intermittent sleep disturbances.For most, it is an occasional night of poor sleep or daytime sleepiness. However, the Institute of Medicine estimates that 50–70 million Americans suffer from a chronic disorder of sleep and wakefulness, which can lead to serious impairment of daytime functioning. In addition, such problems may contribute to or exacerbate medical or psychiatric conditions.Thirty years ago, many such complaints were treated with hypnotic medications...
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Chapter 028. Sleep Disorders (Part 1) Chapter 028. Sleep Disorders (Part 1) Harrisons Internal Medicine > Chapter 28. Sleep Disorders Sleep Disorders: Introduction Disturbed sleep is among the most frequent health complaints physiciansencounter. More than one-half of adults in the United States experience at leastintermittent sleep disturbances. For most, it is an occasional night of poor sleep or daytime sleepiness.However, the Institute of Medicine estimates that 50–70 million Americans sufferfrom a chronic disorder of sleep and wakefulness, which can lead to seriousimpairment of daytime functioning. In addition, such problems may contribute toor exacerbate medical or psychiatric conditions. Thirty years ago, many such complaints were treated with hypnoticmedications without further diagnostic evaluation. Since then, a distinct class ofsleep and arousal disorders has been identified. Physiology of Sleep and Wakefulness Most adults sleep 7–8 h per night, although the timing, duration, andinternal structure of sleep vary among healthy individuals and as a function of age.At the extremes, infants and the elderly have frequent interruptions of sleep. In the United States, adults of intermediate age tend to have oneconsolidated sleep episode per day, although in some cultures sleep may bedivided into a mid-afternoon nap and a shortened night sleep. Two principal systems govern the sleep-wake cycle: one actively generatessleep and sleep-related processes and another times sleep within the 24-h day.Either intrinsic abnormalities in these systems or extrinsic disturbances(environmental, drug- or illness-related) can lead to sleep or circadian rhythmdisorders. States and Stages of Sleep States and stages of human sleep are defined on the basis of characteristicpatterns in the electroencephalogram (EEG), the electrooculogram (EOG—ameasure of eye-movement activity), and the surface electromyogram (EMG)measured on the chin and neck. The continuous recording of this array ofelectrophysiologic parameters to define sleep and wakefulness is termedpolysomnography. Polysomnographic profiles define two states of sleep: (1) rapid-eye-movement (REM) sleep, and (2) non-rapid-eye-movement (NREM) sleep. NREMsleep is further subdivided into four stages, characterized by increasing arousalthreshold and slowing of the cortical EEG. REM sleep is characterized by a low-amplitude, mixed-frequency EEGsimilar to that of NREM stage 1 sleep. The EOG shows bursts of REM similar tothose seen during eyes-open wakefulness. Chin EMG activity is absent, reflectingthe brainstem-mediated muscle atonia that is characteristic of that state. Organization of Human Sleep Normal nocturnal sleep in adults displays a consistent organization fromnight to night (Fig. 28-1). After sleep onset, sleep usually progresses throughNREM stages 1–4 within 45–60 min. Slow-wave sleep (NREM stages 3 and 4)predominates in the first third of the night and comprises 15–25% of totalnocturnal sleep time in young adults. The percentage of slow-wave sleep is influenced by several factors, mostnotably age (see below). Prior sleep deprivation increases the rapidity of sleeponset and both the intensity and amount of slow-wave sleep. Figure 28-1