Overnight PSG

The day before sleep studies, all GSs and patients with OSA were required to abstain from drinking caffeinated or alcoholic beverages. Overnight PSG monitoring was performed on all patients with OSA and GSs using the Respironics LE-Series physiological monitoring system (Alice 5 LE, Respironics, Orlando, FL, USA). PSG was recorded from approximately 10 pm to 6 am the next day. The electroencephalogram (EEG), electrooculogram (EOG), electrocardiogram, chin electromyogram (EMG), oral and nasal airflow, thoracic and abdominal movements, body position, oxygen saturation (SaO₂), and snoring were recorded. According to the American Academy of Sleep Medicine (AASM) guidelines,⁴² the EEG derivations (from frontal, central, occipital regions: F4/M1, C4/M1, O2/M1; and back up derivations: F3/M2, C3/M2, and O1/M2), EMG (located in the three chin electrodes and the middle of the right anterior tibialis), and EOG (located in the cornea and retina) were recorded. Sleep latency, total sleep time, sleep efficiency, sleep stages, arousal, and respiratory events were also recorded. According to the AASM manual, an obstructive apnea was defined as a reduction in airflow ≥90% lasting at least 10 seconds and associated with persistent respiratory effort; hypopnea was defined as a reduction in airflow ≥30% lasting at least 10 seconds and accompanied with a 4% or greater oxygen desaturation.⁴² The AHI was calculated as the average of the total number of apnea and hypopnea events experienced per hour of sleep. The arousal index (AI) was computed as the mean number of EEG arousals per hour of sleep.