Chest
Volume 134, Issue 6, December 2008, Pages 1310-1319
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Postgraduate Education Corner
Contemporary Reviews in Sleep Medicine
Technical Review of Polysomnography

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Polysomnography has developed from our understanding of sleep and its associated physiologic processes. This important tool extends the clinical examination into dynamic states that typically do not permit intrusive inspection. The two critical components of polysomnography are the determination of sleep-wake stage and identification of related bodily processes. In this article, the authors review the current standards for clinical polysomnography and discuss technical considerations that influence the accuracy of recorded data.

Section snippets

Sleep State Determination

The principles of sleep stage determination are established by the following three parameters: EEG; EOG; and EMGsub. EEG is the primary parameter used, but muscle tone and eye movements add additional information (Table 1). The importance of EEG in determining sleep stage rests on the recognition of specific EEG figures; therefore, special attention must be directed toward the accurate assessment of EEG.

Sleep Stages

The combination of the EEG, EOG, and EMGsub provides the basis for sleep stage scoring (Table 1). The reader should score the stage based on the majority stage of a 30-s epoch. The wake stage is determined by the presence of a posterior dominant rhythm, REMs, and continued muscle tone. NREM stage 1 sleep is associated with a loss of the posterior dominant rhythm and a slowing of the background typically to a theta frequency. NREM stage 2 sleep is characterized by sleep spindles and K complexes (

Breathing and Respiration

Breathing pattern and respiratory responses are influenced by sleep stage. Light sleep is associated with mild periodic breathing, whereas NREM stage 3 sleep has very regimented breathing. Stage R sleep is associated with the greatest ventilatory variability especially during the bursts of eye movements.14 A decreased physiologic response to low oxygen levels and elevated CO2 levels occurs in NREM and REM sleep.15 These variations in the regulation of breathing reveal potential specific

Ventilatory Consequences: Oxygen and CO2 Measures

The exchange of oxygen and CO2 are measures of adequate ventilation. Oxygen levels are measured via a pulse oximeter transmitting two wavelengths of light to detect pulsation and oxygen saturation of hemoglobin.23 This device depends on a clean connection to the epidermis, and results may be skewed by motion, skin pigmentation, or fingernail discoloration.24 Oximeters are typically placed on a finger or less commonly an earlobe or nose. The device should have a signal average time of not > 3 s.7

Respiratory Scoring

Scoring respiratory events is achieved by properly identifying disruptions in air flow, effort, and oxygenation. All adult respiratory events must be at least 10 s in duration, while for pediatric patients the duration of two breaths is considered to be sufficient to be considered a respiratory event. An apnea is a cessation of air flow and is scored when there is a 90% drop in peak thermal sensor excursion. By definition, a hypopnea is a partial limitation in air flow that is associated with

Cardiac Function

The assessment of cardiac function is usually limited to the electrical field recorded in a modified lead II electrode placement.7 Additional electrodes may aid in the delineation of waveforms and types of rhythms. The scoring of cardiac events is limited to bradycardia and tachycardia events, as noted in Table 3. Less intrusive finger BP monitors may be used to assess cardiovascular function, but these are still relegated mostly to research studies.

Movement

Sleep is a time of relatively limited movement. With NREM sleep, the muscle tone decreases and reaches skeletal atonia with stage R sleep. Limb movements are measured as electromyographic activity of the anterior muscle group of the lower legs and extensor surface of the forearms.7 Surface electrodes are placed < 3 cm apart along the belly of the anterior tibialis muscle on each leg.26 Upper extremity electrodes should be placed over the brachioradialis and wrist extensors. The electrode wires

Behavior Monitoring

Behaviors are best recorded with time-synchronized audio and video recording. Current standard infrared video cameras with infrared light sources provide images of excellent quality. Patients do not perceive the infrared light, but the viewer may see fine details of movement and behaviors. Continuous audiovisual recordings should be time-linked to the polysomnogram.5 This permits association of physiologic data with discrete behaviors and aids with detecting other events such as the detection

Other Parameters

Other physiologic parameters can be measured during polysomnography including but not limited to the following: esophageal acid levels; core body temperature; penile tumescence; sweat levels; and hormonal levels. Each of these provides additional information and associations of sleep-related physiology. As our understanding of the interrelationships between physiology and sleep grows, so too will our ability to identify individuals with specific state-dependent dysfunction.

Polysomnography Levels

Polysomnography can encompass many levels of measurements during sleep. The current guidelines specify four levels of studies (Table 4). These range from full attended studies (level I) to single-parameter unattended studies (level IV).27, 28 More importantly, the clinician must remain vigilant to understanding the principles underlying the accurate assessment of state and associated physiology while understanding the limitations of the current tools used in unlocking the complex mysteries of

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    The authors have reported to the ACCP that no significant conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.

    Reproduction of this article is prohibited without written permission from the American College of Chest Physicians (www.chestjournal.org/misc/reprints.shtml).

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