P series recording system

All participants underwent unattended, in-home, overnight PSG, as previously described using a Compumedics P-series recording system (Compumedics). The recording montage included a C3-A2 and C4-A1 electroencephalogram, left and right electrooculograms, chin electromyogram, single-lead electrocardiogram, airflow by an oral-nasal thermistor, oxyhemoglobin saturation by pulse oximetry, measurement of thoracic and abdominal effort by impedance plethysmography, and body position (by mercury strain gauge). Sleep stage scoring of all nocturnal recordings was conducted by trained technicians using the Rechtschaffen and Kales criteria at a centralized reading center (34 ). Apnea was identified if airflow was absent or nearly absent at ≥10 s (35 (link)). Hypopnea was identified and defined as a discernible reduction in airflow or thoracoabdominal movement (≥30% below baseline values) occurring for ≥10 s (35 (link)). These data were defined and scored using the apnea–hypopnea index (AHI) in various ways, and we chose the recommended hypopnea criteria of the American Academy of Sleep Medicine manual (10 ) (i.e., AHI was defined as the number of apneas or hypopneas, each associated with a 3% decrease in oxygen saturation per hour of sleep).

The in-lab polysomnogram for the patients recruited from the sleep center included recordings of C3 and C4 electroencephalograms, right and left electrooculograms, and submental and bilateral anterior tibialis electromyograms. Sleep-stage scoring was performed in 30-second epochs. Respiration was monitored with a nasal pressure transducer, nose and mouth thermocouples, and thoracic and abdominal strain gauges. Recording of the oxyhemoglobin saturation (SpO₂) was obtained with Biox 3700 pulse oximeter (Ohmeda, Englewood, CO) at 10 Hz and averaged over each 30-second epoch. Apneas were identified if airflow was absent in thermocouples and nasal cannula channels for at least 10 seconds. Hypopneas were identified if there was at least 30% reduction in airflow for at least 10 seconds accompanied with at least 4% oxyhemoglobin desaturation. AHI was determined as the frequency of apneas and hypopneas per hour of total sleep time. The in-lab polysomnography was conducted using the Embla N-7000 system (Natus Medical, Pleasanton, CA). Polysomnography for the community participants was performed at home, using the Compumedics P-series recording system (Compumedics, Abbotsford, Victoria, Australia).