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Polysomnographic record of REM Sleep . EEG highlighted by red box. Eye movements highlighted by red line.

Polysomnography or PSG is a multi-parametric test used in the study of sleep and as a diagnostic tool in sleep medicine. The test result is called a polysomnogram, also abbreviated PSG. The name is derived from Greek and Latin roots: the Greek 'poly' for multi-channel (many), the Latin 'somnus' (sleep), and the Greek 'graphein' (to write).

Normal patterns of human sleep were first discovered by Loomis, Harvey and Hobart in 1935.[citation needed] The discovery and documentation of REM (Rapid Eye Movement) sleep was accomplished by Nathaniel Kleitman, Eugene Aserinsky, William C. Dement, and graduate students at the University of Chicago in the early 1950s.[1] Surprisingly, no other sleep laboratory findings were published until 1959.

A Manual of Standardized Terminology, Techniques, and Scoring System for Sleep Stages of Human Subjects, edited by Allan Rechtschaffen and Anthony Kales, was adopted in 1968.[citation needed]

Polysomnography is a comprehensive recording of the biophysiological changes that occur during sleep. It is usually performed at night, when most people sleep, though some labs can accommodate shift workers and people with circadian rhythm sleep disorders and do the test at other times of day. The PSG monitors many body functions including brain (EEG), eye movements (EOG), muscle activity or skeletal muscle activation (EMG) and heart rhythm (ECG) during sleep. After the identification of the sleep disorder sleep apnea in the 1970s, the breathing functions respiratory airflow and respiratory effort indicators were added along with peripheral pulse oximetry.

Polysomnography is used to diagnose, or rule out, many types of sleep disorders including narcolepsy, restless legs syndrome, REM behavior disorder, parasomnias, and sleep apnea. It is often ordered for patients with complaints of daytime fatigue or sleepiness that may be caused by interrupted sleep. Although it is not directly useful in diagnosing circadian rhythm sleep disorders, it may be used to rule out other sleep disorders.

Increasingly, polysomnography is being supplemented or replaced by Actigraphy in cases where longitudinal or large scale data sets need to be generated, or when PSG is not a cost-efficient option

Pediatric polysomnography patient,
Children's Hospital (Saint Louis), 2006

Contents

The polysomnogram

A polysomnogram will typically show a minimum of eleven channels requiring a minimum of 22 wire attachments to the patient. Two channels are for the EEG, one or two measure airflow, one is for chin movements, one or more for leg movements, two for eye movements (EOG), one for heart rate and rhythm, one for oxygen saturation and one each for the belts which measure chest wall movement and upper abdominal wall movement.

Wires for each channel of recorded data lead from the patient and converge into a central box, which in turn is connected to a computer system for recording, storing and displaying the data. During sleep the computer monitor can display multiple channels continuously. In addition, most labs have a small video camera in the room so the technician can observe the patient visually from an adjacent room.

The EEG or electroencephalogram will generally use four "exploring" electrodes and two "reference" electrodes, unless a seizure disorder is suspected, in which case more electrodes will be applied to document the appearance of seizure activity. The exploring electrodes are usually attached to the scalp near the central (top) and occipitial (back) portions of the brain via a paste that will conduct electrical signals originating from the neurons of the cortex. These electrodes will provide a readout of the brain activity that can be "scored" into different stages of sleep (1, 2, 3, 4, REM, and Wakefulness, where, recently, stages 3 and 4 are combined and together are called stage 3).

The EOG or electrooculogram uses two electrodes; one that is placed slightly out from and above the outer canthus of the right eye and one that is placed slightly out and below the outer canthus of the left eye. These electrodes pick up the activity of the eyes in virtue of the electropotential difference between the cornea and the retina (the cornea is positively charged relative to the retina). This determines when REM sleep occurs, of which rapid eye movements are characteristic, and also essentially aids in determining when sleep occurs.

The EMG or electromyogram typically uses four electrodes to measure muscle tension in the body as well as to monitor for an excessive amount of leg movements during sleep (which may be indicative of Periodic Limb Movement Disorder, PLMD). Two leads are placed on the chin with one above the jaw line and one below. This, like the EOG, helps determine when sleep occurs as well as REM sleep. Sleep generally includes relaxation and so a marked decrease in muscle tension occurs. A further decrease in skeletal muscle tension occurs in REM sleep. A person becomes partially paralyzed to make acting out of dreams impossible, although people that do not have this paralysis can suffer from REM Behavior Disorder. Finally, two more leads are placed on the anterior tibialis of each leg to measure leg movements.

Though a typical ECG (or EKG for Electrokardiogram) would use ten electrodes, only two or three are used for a polysomnogram. They can either be placed under the collar bone on each side of the chest, or one under the collar bone and the other six inches above the waist on either side of the body. These electrodes measure the electrical activity of the heart as it contracts and expands, recording such features as the "P" wave, "QRS" complex, and "T" wave. These can be analyzed for any abnormalities that might be indicative of an underlying heart pathology.

Nasal and oral airflow can be measured using pressure transducers, and/or a thermocouple, fitted in or near the nostrils; the pressure transducer is considered the more sensitive.[citation needed] This allows the clinician/researcher to measure rate of respiration and identify interruptions in breathing. Respiratory effort is also measured in concert with nasal/oral airflow by the use of belts. These belts expand and contract upon breathing effort.

Pulse oximetry helps determine changes in blood oxygen levels that often occur with sleep apnea and other respiratory problems. The pulse oximeter fits over a finger tip or an ear lobe.

Snoring may be recorded with a sound probe over the neck, though more commonly the sleep technician will just note snoring as "mild", "moderate" or "loud" or give a numerical estimate on a scale of 1 to 10.

References

  1. ^ Aserinsky, E.; Kleitman, N. (September 4, 1953). "Regularly Occurring Periods of Eye Motility, and Concomitant Phenomena, during Sleep". Science 118 (3062): 273-274. 

Further reading

  • Pressman MR (2002). Primer of Polysomnogram Interpretation. Boston: Butterworth Heinemann. ISBN 0-7506-9782-2. 
  • Berry RB (2003). Sleep Medicine Pearls. Philadelphia: Hanley & Belfus. ISBN 1-56053-490-7. 
  • Bowman TJ (2003). Review of Sleep Medicine. Boston: Butterworth Heinemann. ISBN 0-7506-7392-3. 
  • Kryger MH, Roth T, Dement WC (2005). Principles and Practice of Sleep Medicine (4th ed.). Philadelphia: Elsevier Saunders. ISBN 978-0-7216-0797-9. 
  • Kushida CA, Littner MR, Morgenthaler TM, et al. (2005). "Practice parameters for the indications for polysomnography and related procedures: An update for 2005". Sleep 28: 499-519. 

External links

Retrieved from "http://en.wikipedia.org/wiki/Polysomnography"

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