You are in: eMedicine Specialties > Neurology > Sleep-Related Diseases Polysomnography: Overview and Clinical ApplicationArticle Last Updated: Mar 30, 2007AUTHOR AND EDITOR INFORMATIONSection 1 of 11
  Author: Carmel Armon, MD, MHS, Professor of Neurology, Tufts University School of Medicine, Chief, Division of Neurology, Baystate Medical Center, Springfield, Massachusetts Carmel Armon is a member of the following medical societies: American Academy of Neurology, American Academy of Sleep Medicine, American Association of Neuromuscular and Electrodiagnostic Medicine, American Clinical Neurophysiology Society, American College of Physicians, American Epilepsy Society, American Medical Association, American Neurological Association, American Stroke Association, Massachusetts Medical Society, Movement Disorders Society, and Sigma Xi Coauthor(s): Asim Roy, MD, Assistant Clinical Professor of Neurology, Tufts University School of Medicine; Consulting Staff, Division of Neurology, Baystate Medical Center; William J Nowack, MD, Associate Professor, Department of Neurology, Epilepsy Center, University of Kansas Medical Center Editors: Anthony M Murro, MD, Laboratory Director, Professor, Department of Neurology, Medical College of Georgia; Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine; Norberto Alvarez, MD, Assistant Professor, Department of Neurology, Harvard Medical School; Consulting Staff, Department of Neurology, Boston Children's Hospital; Selim R Benbadis, MD, Professor, Director of Comprehensive Epilepsy Program, Departments of Neurology and Neurosurgery, University of South Florida School of Medicine, Tampa General Hospital; Nicholas Y Lorenzo, MD, Chief Editor, eMedicine Neurology; Consulting Staff, Neurology Specialists and Consultants Author and Editor Disclosure Synonyms and related keywords: PSG, polysomnogram, sleep study, rapid eye movement study, REM study, sleep, wakefulness, multiple sleep latency testing, MSLT, electroencephalography, EEG, electrooculogram, EOG, electromyography, EMG, overnight polysomnography, oPSG, REM sleep, slow-wave sleep, SWS, non-REM sleep, dyssomnias, parasomnias, sleep disorders, abnormalities of sleep, obstructive sleep apnea, sleep disordered breathing, central sleep apnea, mixed sleep apnea, complex sleep apnea INTRODUCTIONSection 2 of 11
  Nocturnal, laboratory-based polysomnography (PSG) is the most commonly used test in the diagnosis of obstructive sleep apnea syndrome (OSAS). It is often considered the criterion standard for diagnosing OSAS, determining the severity of the disease, and evaluating various other sleep disorders that can exist with or without OSAS. PSG consists of a simultaneous recording of multiple physiologic parameters related to sleep and wakefulness (see Image 1). PSG can directly monitor and quantify the number of respiratory events (ie, obstructive, central, or complex) and the resultant hypoxemia and arousals related to the respiratory events or even independent of the respiratory events. A single-night PSG is usually adequate to determine if OSAS is present and the degree of the disorder. However, night-to-night variability may exist in patients who have a high probability but a low apnea index. In addition, variability in laboratory equipment, scoring technique, and interscorer reliability may also play roles. As is well known, PSG scoring also usually varies from laboratory to laboratory. PSG is used to evaluate abnormalities of sleep and/or wakefulness and other physiologic disorders that have an impact on or are related to sleep and/or wakefulness. PARAMETERS MONITOREDSection 3 of 11
Assessment of sleep stages requires 3 studies: electroencephalography (EEG), electrooculography (EOG), and surface electromyography (EMG). One EEG channel (central channel with an ear reference provides the best amplitude) is used to monitor sleep stage. However, most laboratories use 2 central channels and 2 occipital channels, with ear references as an adjunct to help identify sleep latency and arousals. A 10- to 20-electrode placement system is used to determine the location of these channels. Additional EEG channels can be used, particularly in patients with epilepsy (ie, a full 10-20 montage). Two EOG channels are used to monitor both horizontal and vertical eye movements. Electrodes are placed at the right and left outer canthi, one above and one below the horizontal eye axis. The electrodes pick up the inherent voltage within the eye; the cornea has a positive charge and the retina has a negative charge. Evaluation of the eye movements is necessary for 2 reasons. First is for documentation of the onset of rapid eye movement (REM) sleep, and second is to note the presence of slow-rolling eye movements that usually accompany the onset of sleep. One EMG channel (usually chin or mentalis and/or submentalis) is used to record atonia during REM sleep or lack of atonia in patients with REM-related parasomnias. To assess bruxism, the EMG electrodes can be placed over the masseter. The EMG recording from other muscle groups is assessed for other sleep disorders. For example, the anterior tibialis EMG is helpful for assessing periodic limb movements during sleep and the intercostal EMG is used as adjunctive help for determining effort during respiratory events. Other parameters that can be monitored in a sleep study include the following:
Optional parameters that can be monitored in a sleep study include the following:
PROCEDURESSection 4 of 11
In 1992, the Office of Technology Assessment of the Agency of Health Care Policy and Research recommended, in an evidence-based assessment, 2 tests as having been studied sufficiently. Both tests are performed in a sleep laboratory. The first is overnight PSG, which is an overnight recording of the patient's sleep. The second is multiple sleep latency testing (MSLT), which records multiple naps throughout a day (usually four 20-min naps separated by 90 min). Standard sleep studies usually use the overnight PSG (may be performed over several nights). If daytime sleepiness is an issue and cannot be fully explained by the overnight study results, an MSLT should be performed the next day. Limitations usually stem from the fact that recording conditions may not reflect what happens during a regular night in the patient's home. Although diagnosing a sleep problem on the basis of a recording over a single night is common practice, some authorities caution that more than one night of recording may be necessary so the patient can become comfortable with unfamiliar surroundings and sleep more naturally. This effect is greatest on the first night in the sleep laboratory (ie, first-night effect). Sporadic events may be missed with a single-night PSG. External factors that disturb the subject's sleep may be present in the home but absent from the controlled environment of the sleep laboratory. Patient preparation is important so that the patient sleeps naturally. Patient instructions include the following:
High costs and long waiting lists have prompted the exploration of alternative methods of evaluation. Although the following studies may have usefulness in specific clinical situations, Bloch concludes that their role compared with conventional sleep studies remains controversial.
STAGING OF SLEEPSection 5 of 11
EEG background
Sleep spindle
K complexes
Awake stage
Stage 1
Stage 2
Stage 3
Stage 4
REM sleep
RESPIRATORY EVENTS AND LEG MOVEMENT SCORINGSection 6 of 11
Basic rules
Obstructive apnea
Hypopnea
Mixed apnea
Central apnea
Periodic limb movement
SUMMARYSection 7 of 11
Standard analysis still consists of reviewing each of the parameters recorded. Overnight parameters (eg, times of lights on/off, total time in bed, total sleep time, sleep latency, REM latency) are collected. The overnight recording is divided into epochs of approximately 30 seconds. The standard EEG, EMG, and EOG recordings are evaluated, and the predominant stage of sleep (according to the manual of Rechtschaffen and Kales) is then assigned to the entire epoch. Total time and relative proportion of the night spent in each of the stages and in REM and non-REM sleep are calculated. Latencies to REM and slow-wave sleep are reported. Stages of sleep, any abnormalities noted with EEG, and periodic limb movements are reported. Respiratory activity (eg, apneic or hypopneic episodes, oxygen desaturations) is correlated with sleep stages. Other parameters, such as body position, are recorded. If needed, esophageal pH or penile tumescence can also be recorded. If a sleep apnea syndrome is diagnosed, the patient undergoes a trial and titration of positive airway pressure either (1) in a partial-night PSG titration study if he or she meets criteria based on individual laboratory criteria (generally, apnea-hypopnea index >30) or (2) in a full-night PSG titration study. DISORDERS EVALUATED WITH POLYSOMNOGRAPHYSection 8 of 11
Dyssomnias (disorders of initiating or maintaining sleep)
Parasomnias
TREATMENTSection 9 of 11
Treatment is determined by the disorder diagnosed using PSG and/or MSLT. Patient education For excellent patient education resources, visit eMedicine's Sleep Disorders Center. In addition, see eMedicine's patient education article Disorders That Disrupt Sleep (Parasomnias). MULTIMEDIASection 10 of 11
REFERENCESSection 11 of 11
Polysomnography: Overview and Clinical Application excerpt Article Last Updated: Mar 30, 2007 | |||||||
