Polysomnography

Polysomnography (PSG), a type of sleep study, 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 πολύς (polus for 'many, much', indicating many channels), the Latin somnus ('sleep'), and the Greek γράφειν (graphein, 'to write').Mr. J----, age 41, 5′8″ tall, 265 lbs., came to the sleep lab to rule out obstructive sleep apnea. He complains of some snoring and daytime sleepiness. His score on the Epworth Sleepiness Scale is elevated at 15 (out of possible 24 points), affirming excessive daytime sleepiness (normal is <10/24).Mr. B____, age 38, 6 ft. tall, 348 lbs., came to the Hospital Sleep Lab to diagnose or rule out obstructive sleep apnea. This polysomnogram consisted of overnight recording of left and right EOG, submental EMG, left and right anterior EMG, central and occipital EEG, EKG, airflow measurement, respiratory effort and pulse oximetry. The test was done without supplemental oxygen. His latency to sleep onset was slightly prolonged at 28.5 minutes. Sleep efficiency was normal at 89.3% (413.5 minutes sleep time out of 463 minutes in bed). Polysomnography (PSG), a type of sleep study, 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 πολύς (polus for 'many, much', indicating many channels), the Latin somnus ('sleep'), and the Greek γράφειν (graphein, 'to write'). Type I polysomnography, a sleep study performed overnight while being continuously monitored by a credentialed technologist, 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 the day. The PSG monitors many body functions, including brain activity (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 no longer includes NPT, Nocturnal Penile Tumescence, for monitoring of erectile dysfunction, as it is reported that all male patients will experience erections during phasic REM sleep, regardless of dream content. Limited channel polysomnography, or unattended home sleep tests, should be referenced as Type II – IV channel polysomnography. With some controversy, polysomnography is best performed by technicians and technologists who are specifically licensed and accredited in sleep medicine. However, at times nurses and respiratory therapists are allowed to perform polysomnography despite lack of specific knowledge and training in this area. In general, many information can be extrapolated from the polysomnography; some can be directly related to the sleep, such as the sleep onset latency (SOL), the REM-sleep onset latency, the number of awakenings during the sleep-period, the total sleep duration, percentages and durations of every sleep stage, and the number of arousals. But there can be also other information, crucial for many diagnostics, that are not directly linked with the sleep, such as movements, respiration, cardiovascular parameters. In any case, through the polysomnographic evaluation, other information can be obtained (such as, for example, body temperature or esophageal pH) according to the patient's or the study's needs. Video-EEG polysomnography is a technique combining polysomnography and video-recording, which has been described to be even more effective than only polysomnography for the evaluation of some sleep troubles such as parasomnias, because it allows to more easily correlate EEG signals, polysomnography and behaviors. Polysomnography is used to diagnose, or rule out, many types of sleep disorders, including narcolepsy, idiopathic hypersomnia, periodic limb movement disorder (PLMD), REM behavior disorder, parasomnias, and sleep apnea. Although it is not directly useful in diagnosing circadian rhythm sleep disorders, it may be used to rule out other sleep disorders. The use of polysomnography as a screening test for persons having excessive daytime sleepiness as a sole presenting complaint is controversial. A polysomnogram will typically record a minimum of 12 channels requiring a minimum of 22 wire attachments to the patient. These channels vary in every lab and may be adapted to meet the doctor's requests. There is a minimum of three channels for the EEG, one or two measure airflow, one or two are for chin muscle tone, one or more for leg movements, two for eye movements (EOG), one or two 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. The movement of the belts is typically measured with piezoelectric sensors or respiratory inductance plethysmography. This movement is equated to effort and produces a low-frequency sinusoidal waveform as the patient inhales and exhales. Because movement is equated to effort, this system of measurement can produce false positives. It is possible, especially during obstructive apneas, for effort to be made without measurable movement.