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Polysomnography Filters and Calibrations Name Institution Filter Settings and Sensitivity Filters used for the various polysomnographic processes require predefined filtering ranges to help define their maximum and minimum limits. The bandwidth of recorded parameters helps in selection of these filters. Usually, filters are set slightly above the bandwidth range to allow the sloppiness of the “frequency response curve” and ensure that all essential frequencies are preserved (Butkov, 2007, p. 264). A typical filter used for routine EEG should meet various specifications. First, it should make use of broad-pass analog filter settings for acquisition (scalp: 0.1-70 Hz, intracranial 0.1-100 Hz). Therefore, when recording an EEG that falls in the range of 0.5-25 Hz, the low-frequency filter should be set at 0.3 Hz while the high-frequency filter is set at 30 Hz or 35 Hz to allow full signal resolution at either end of the spectrum and cancel out undesirable frequencies outside the predefined range. Filter settings for EOG are similar to those of EEG, and they aid in the identification of both slow and rapid eye movements. The EMG operates with filter settings at a low frequency of 10 Hz and a high of 90-100 Hz. Sometimes, these frequencies exceed 100 Hz, but avoiding such high frequencies is important to prevent signal interference. EKG, or ECG, is recorded as a “single-channeled, modified lead II configuration,” whose main function is to detect heart rhythms and identify dysrhythmias. Hence, filter settings of low frequencies at 1 Hz and high frequencies at 30-35 Hz adequately meet their intended purpose (Butkov, 2007). Children hardly remain stable when a
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