major findings is that OSA contributes an independent risk for the development of Sleep and breathing cardiovascular disease after accounting for other known risk factors. Conse- disorders: the genesis quently, the identification of these dis- of obstructive sleep apnea orders and their treatment may help to prevent morbidity and mortality. The prevalence of these disorders poses sig- BRIAN H. FORESMAN, DO nificant issues for the primary care physi- cians. Sleep physiology Basic sleep physiology, although rarely Sleep encompasses approximately a third of our lives; however, sleep and the discussed in osteopathic medical schools, disorders of sleep are not widely understood. Data suggest that sleep plays a is essential in the understanding of OSA restorative role in physiologic mechanisms and that long-term disruption of sleep and related disorders. Sleep is classified may contribute to the development of disease. Nearly a third of the adult popu- in two major states: non–rapid-eye-move- lation is chronically afflicted by sleep disorders, and substantial economic loss is ment (non-REM) sleep and REM sleep. attributable to these disorders in terms of lost time, inefficiency, and accidents. Of Non-REM sleep comprises stages 1, 2, 3, the sleep disorders, obstructive sleep apnea (OSA) is one of the more common, clin- and 4. Stages 3 and 4 comprise slow- ically affecting up to 5% of the adult population. Obstructive sleep apnea con- wave sleep and are characterized as deep tributes to the development of disease and has an adverse impact on daytime sleep. As one progresses from stage 1 to functioning in those affected by the disease. This article reviews basic sleep phys- stage 4, sleep becomes deeper and the iology, how these physiologic mechanisms are disrupted by OSA, and some of the number of slow waves increases. These techniques for treating patients with this disorder. stages give way to the development of (Key words: sleep disorders, obstructive sleep apnea, daytime sleepiness, REM sleep, that stage of sleep in which continuous positive airway pressure, circadian rhythm) the majority of dreams occur. During REM sleep, the stimuli that create dreams also cause signals to be gener- ated down the motor pathways of the leep encompasses approximately a gest that 10% to 15% of the general brainstem. Were it not for a secondary Sthird of our lives; however, the phys- population have frequent daytime sleepi- mechanism, these signals would initiate iologic processes active during sleep or ness, while some select groups may motor activity consistent with the dream sleep’s role in maintaining physiologic approach 35%.1 Sleep-related breathing content. The simultaneous activation of homeostasis is largely unknown. Until disorders are one of the most common an inhibitory pathway causes muscle the early 1980s, the physiologic need for disorders that may affect sleep and cause atonia in the majority of the skeletal sleep had not been convincingly estab- excessive daytime sleepiness; obstructive muscles and prevents people from acting lished. Now, data suggest that sleep plays sleep apnea (OSA) is the major disorder out their dreams. For individuals who a restorative role in physiologic mecha- in this class. In the general population, rely on the skeletal muscles, and espe- nisms and long-term disruption of sleep these disorders are not trivial and they are cially the accessory muscles, the muscle may contribute to the development of often complicated by other disorders, atonia compromises ventilation and may disease. Data regarding the prevalence medical conditions, or behavioral issues. result in hypoventilation or apnea. The of sleep disorders suggest that nearly a Symptomatic OSA affects between 2% characteristics of each of these sleep third or more of the adult population is and 4% of women and 5% to 9% of stages are briefly outlined in Table 1. chronically afflicted by sleep disorders men, depending on the criteria used.1 and a substantial loss in terms of time Although there appears to be an “at- Sleep architecture and accidents is related to these disorders. risk” population who is not symptomatic, The pattern of sleep stages that occurs Estimates from the United States sug- up to 9% of women and 24% of men during a night’s sleep constitutes the have the physiologic hallmarks. This may sleep architecture. Typically, an individ- be especially important as these individ- ual progresses from stage 1 to stage 2 Correspondence to Brian H. Foresman, DO, uals may be at risk for other disorders. to slow-wave sleep and then to REM Clinical Assistant Professor of Medicine, Medi- Recent studies conducted through the sleep in a recurring pattern. Each cycle, cal Director, Indiana University Center For Sleep National Institutes of Health have begun from the lighter stages of sleep through Disorders, Indiana University School of Medicine, Indianapolis, IN 46202-6602. to define the relationships between OSA the end of REM, typically takes 60 to 90 Email: [email protected] and cardiovascular disease.2 One of the minutes. As the night progresses, each Foresman • Sleep and breathing disorders: the genesis of obstructive sleep apnea JAOA • Vol 100 • No 8 • Supplement to August 2000 • S1 Table 1 Characteristics of Sleep Stages* Background Special Stage EEG EMG EOG characteristics Ⅵ Wake† Mixed frequency Relatively Eye movements May observe beta with more than 50% high tonic and blinks waves in EEG of the epoch alpha waves Ⅵ Stage 1† Low voltage, Tonic EMG less SREMs in early Occasional vertex mixed frequency, than wake portion sharp waves in EEG; less than 50% alpha absence of spindles waves, predominance and K complexes of 2-Hz to 7-Hz activity Ⅵ Stage 2 Low voltage, Similar to stage 1 Absence of REMs Intermittent mixed frequency tonic EMG or SREMs K complexes‡ and/or may have some slow- sleep spindles‡ wave activity Ⅵ Stage 3 Slow-wave activity Similar to stage 1 Absence of REMs Sleep spindles and (Ͻ2 Hz) of 75 ⌽V tonic EMG or SREMs K complexes may or amplitude in 20% to 50% may not be present of the epoch Ⅵ Stage 4 Same as stage 3 Same as stage 3 Same as stage 3 Same as stage 3; but greater than 50% clearly identifiable of the epoch consists K complexes are rare of delta waves Ⅵ Stage REM† Low voltage, mixed Low voltage, Episodic REMs Absence of sleep frequency,‡ tonic EMG, lower (Phasic REM)‡ spindles and K 5-Hz to 7-Hz “sawtooth” than preceding complexes; may see waves frequently seen stage‡ intermittent alpha but not required wave activity Key: EEG ϭ electroencephalogram; EMG ϭ electromyogram; EOG ϭ electro-oculogram; REM ϭ rapid eye movement; SREM ϭ slow rolling eye movement. *A scoring epoch is typically 30 seconds. If paper systems are used, the paper speed is 10 mm/s. †For more details and exceptions see criteria in Rechtschaffen A, Kales A. A Manual of Standardized Terminology, Techniques and Scoring System for Sleep Stages of Human Subjects. Los Angeles, Calif: Brain Information Service/Brain Research Institute, University of California; 1968. ‡Characteristic that must be present. cycle contains less slow-wave sleep and commonly, individuals who are getting ting occurs through a process of entrain- more REM sleep. The amount of each fewer than 6 hours of sleep each night are ing mediated by three primary processes. sleep stage and the amount of sleep sleep deprived. The first is exposure to light on awak- required by an individual changes with ening. The light stimulates neural signals age. Very young children require 14 to 16 Circadian patterns from the eye through the suprachiasmatic hours of sleep, with such requirement The timing of sleep is important in the nucleus that helps to regulate our internal declining to 8 to 10 hours for teenagers overall assessment of sleep disorders. “clock” and biologic rhythms. The sec- and young adults. Slow-wave sleep and Physiologic rhythms cycle across the ond mechanism is the pattern of daily REM sleep predominate. As individuals course of a single day. For most individ- activities. The stimulation arising from move into adulthood, their typical sleep uals, the duration of these rhythms, these activities and our interactions with requirement decreases into the range of 6 referred to as “circadian rhythms,” is other people reinforces the sleep-wake to 9 hours. Some individuals may require about 26 hours. These internal rhythms cycle. The final mechanism involves pat- more sleep or less sleep, but they represent must be reset each day to maintain con- terns of eating. Food is a very potent less than 5% of the population. Most sistency with the environment. This reset- stimulus with regard to our sleep-wake S2 • JAOA • Vol 100 • No 8 • Supplement to August 2000 Foresman • Sleep and breathing disorders: the genesis of obstructive sleep apnea Table 2 Physiologic Changes in Respiratory Control With Sleep Slow-wave Stage 1 Stage 2 (stages 3 and 4) Rapid-eye- Variable sleep sleep sleep movement sleep Ⅵ Source of control Metabolic Metabolic Metabolic Nonmetabolic Ⅵ Respiratory pattern Periodic Regular Regular Irregular Ⅵ Central apneas/hypopneas Often Rare Absent Frequent Ⅵ Response to metabolic stimuli Variable Mild decrease Mild decrease Moderate decrease Ⅵ Chest wall movement Phasic Phasic Phasic Occasionally paradoxical Table 3 Characteristics of Respiratory Events Respiratory event Duration Airflow Effort Desaturation Arousal Ⅵ Obstructive apnea At least 10 s Absent at Proportionately Not required Not required some point greater than in the event flow; crescendo effort common Ⅵ Central apnea At