Polysomnography for Obstructive Sleep Apnea

In-laboratory PSG was performed utilizing ResMed Embla N7000 (ResMed, San Diego, CA, USA) and Embla MPR (Natus Medical, Pleasanton, CA, USA). PSG includes various sensors (i.e. electroencephalogram, electrooculogram, electromyogram of the chin and leg, a nasal cannula, oral–nasal thermistor, bands for the chest and abdomen, pulse oximetry, and a piezoelectric vibration sensor). All of the signals were recorded using RemLogic software (version 3.41, Embla, Thornton, CO, USA) and scored by certified PSG technologists per the Americana Academy of Sleep Medicine (AASM) Scoring Manual.²⁵ For snoring which serves as an indicator of upper airway obstruction, these events were assessed by a piezoelectric vibration sensor placed on the triangle of the neck. Technically, this sensor measures frequencies of oscillations at the skin surface, thereby generating a piezoelectric signal to represent the snoring waveform. Snoring events were defined as protruding from the background and being synchronized with breathing, except for the body movement time. Piezoelectric signals were recorded at a sampling rate of 200 Hz and with AASM-recommended filter settings (low frequency of 10 Hz and high frequency of 100 Hz). Regarding OSA severity, the AHI, defined as the number of apneic and hypopneic events of the total sleep time, was obtained, and this index was further divided into four OSA levels, namely normal (AHI: <5 times/h), mild (5 ≤ AHI <15 times/h), moderate (15≤ AHI <30 times/h), and severe (AHI ≥30 times/h).^{26 (link)}