![]() ![]() To further classify apneas as obstructive, mixed or central chest and abdominal sensors are used to evaluate respiratory effort. Airflow via nasal pressure sensors detects partial airflow limitation or hypopneas, and airflow via oronasal thermal flow sensors detects complete airflow obstruction or apneas. EOG and chin EMG help with the evaluation of the sleep stage, particularly during rapid eye movement (REM) sleep. EEG is recorded at the frontal, central, and occipital regions and is used to define sleep stages. Sleep is staged in 30-s epochs with detailed criteria and definitions for wakefulness and each stage of sleep. In order to standardize PSG across sleep labs, the American Academy of Sleep Medicine (AASM) Manual for Scoring of Sleep and Associated Events was developed to provide the universally accepted criteria for standard recording technique and scoring guidelines (AASM Scoring Manual version 2.6, 4). In addition, video recording has led to video PSG (VPSG), which is a standard attribute in the evaluation and assessment of complex behaviors during sleep allowing the capacity to record movements, speech, behaviors including assessment for amnesia, recovery, and patients’ response to questions by the sleep technicians. PSG has become the gold standard for comprehensive monitoring of sleep to evaluate sleep disorders. In recent years, additional parameters were incorporated including electromyography (EMG) tone, electrooculogram (EOG), expanded EEG montages, and transcutaneous or end-tidal capnography. Initially, analog (paper) recordings had limitations in the selected EEG montage and numbers of possible channels, and the digitization in the 1990s allowed for many more parameters to be analyzed. The term polysomnogram was coined in the 1970s and combined continuous EEG, which analyzed sleep states, with respiratory channels, body position sensors, and electrocardiography (ECG). Thereafter, clinicians integrated this technology and incorporated additional physiologic respiratory and cardiac parameters to develop the sleep study. Hans Berger invented electroencephalography (EEG) in the early twentieth century which records electrical cortical activity and calculates relative differences in electrical fields across brain regions. Polysomnography (PSG) is defined as the continuous monitoring and simultaneous recording of physiologic activity during sleep. Because of the limitations of subjective measures of sleep, there is often an inherent need for an objective measure to evaluate sleep quality and disorders which impair sleep.
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