Institute of Sleep Science Entally Kolkata

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 brainactivity (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[2]. In any case, through the polysomnographic evalutation, other information can be obtained (such as, for example, body temperature or esophageal pH) according to the patient’s or the study's needs[3]. 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[4].