Disturbed sleep is one of the most common health complaints that physicians encounter. More than one-half of adults in the United States experience at least intermittent sleep disturbance, and only 30% of adult Americans report consistently obtaining a sufficient amount of sleep. The National Academy of Medicine has estimated that 50–70 million Americans suffer from a chronic disorder of sleep and wakefulness, which can adversely affect daytime functioning as well as physical and mental health. A high prevalence of sleep disorders across all cultures is also now increasingly recognized, and these problems are expected to further increase in the years ahead as the global population ages. Over the last 20 years, the field of sleep medicine has emerged as a distinct specialty in response to the impact of sleep disorders and sleep deficiency on overall health. Nonetheless, over 80% of patients with sleep disorders remain undiagnosed and untreated—costing the U.S. economy over $400 billion annually in increased health care costs, lost productivity, accidents and injuries, and leading to the development of workplace-based sleep health education and sleep disorders screening programs designed to address this unmet medical need.
PHYSIOLOGY OF SLEEP AND WAKEFULNESS
Adults need at least 7 h of sleep per night to promote optimal health, although the timing, duration, and internal structure of sleep vary among individuals. In the United States, adults tend to have one consolidated sleep episode each night, although in some cultures sleep may be divided into a mid-afternoon nap and a shortened night sleep. This pattern changes considerably over the life span, as infants and young children sleep considerably more than older people.
The stages of human sleep are defined on the basis of characteristic patterns in the electroencephalogram (EEG), the electrooculogram (EOG—a measure of eye-movement activity), and the surface electromyogram (EMG) measured on the chin, neck, and legs. The continuous recording of these electrophysiologic parameters to define sleep and wakefulness is termed polysomnography.
Polysomnographic profiles define two basic states of sleep: (1) rapid eye movement (REM) sleep and (2) non–rapid eye movement (NREM) sleep. NREM sleep is further subdivided into three stages: N1, N2, and N3, characterized by increasing arousal threshold and slowing of the cortical EEG. REM sleep is characterized by a low-amplitude, mixed-frequency EEG similar to that of NREM stage N1 sleep, and the EOG shows REMs which tend to occur in flurries or bursts. EMG activity is absent in nearly all skeletal muscles except those involved in respiration, reflecting the brainstem-mediated muscle paralysis that is characteristic of REM sleep.
ORGANIZATION OF HUMAN SLEEP
Normal nocturnal sleep in adults displays a consistent organization from night to night (Fig. 27-1). After sleep onset, sleep usually progresses through NREM stages N1–N3 sleep within 45–60 min. NREM stage N3 sleep (also known as slow-wave sleep) predominates in the first third of the ...