Polysomnography

All patients were monitored with a nocturnal PSG that was performed with multichannel monitoring that included neurophysiological electrodes (electroencephalography electrodes), chest wall motion, abdominal motion, arterial oxygen saturation, and electrocardiography electrodes (Grass-Telefactor Cephalo, An Astro-med Inc. Product Group, 2005, USA). Oronasal airflow was measured using a thermistor. The oxyhemoglobin saturation was monitored with a finger pulse oximeter with a sampling rate of 1 Hz. The body position was measured by a position sensor attached to the anterior chest wall. Signals recorded in the sleep period were manually analyzed (25). Apneas were scored when the airflow decreased by at least 90% from baseline for at least 10 s and were classified as central, mixed, or obstructive depending on the occurrence of thoracoabdominal movements (25). Hypopneas were scored when airflow decreased by at least 30% for ≥10 s and was associated with an oxygen saturation (SaO₂) fall of ≥3%. AHI was calculated as the average number of apneas and hypopneas per hour of recording in the sleep period. An AHI of ≥5 was used to diagnose OSA (26). SaO₂ during the sleep period was automatically analyzed, and after the manual elimination of possible artifacts, mean SaO₂ and lowest nocturnal SaO₂ values were detected. According to their overall AHIs OSA patients were grouped as mild (5–14.9/h) and moderate to severe (>15/h) (25).