Somnoscreen plus

Sleep was recorded using a portable EEG device (SOMNOscreenTM plus, SOMNOmedics GmbH, Randersacker, Germany). Fourteen Ag/AgCl electrodes were applied to the cleansed sites at the scalp, face and upper body of the participants, including Fz, C3, C4, Cz, Pz, Oz, A1, A2, Ground, Electrooculography (left and right), Electromyography (left and right upper chin and beneath chin), Electrocardiography (ECG) (Lead II: left lower rib cage and right clavicle), according to the AASM recommendations [38 ]. EEG recordings were referenced to Cz. All channels were sampled at 256 Hz. To ensure high quality, impedances were kept within a tolerable range (≤20 Ω). Sleep measures of the nap group resemble typical values of nap studies and are summarized in Table 1.Table 1

Descriptive sleep measures of the nap group.

	Duration in minutes Mean (SEM)	Percentage of total sleep time Mean (SEM)
Total sleep time	71.95 (3.74)
NREM1 sleep	7.38 (1.18)	10.15 (1.41)
NREM2 sleep	35.76 (2.76)	51.25 (3.81)
NREM3 sleep	16.14 (3.17)	22.91 (4.49)
REM sleep	6.57 (1.79)	7.92 (2.17)
WASO	6.0 (1.69)	7.64 (2.10)

REM rapid eye movement sleep, NREM non REM sleep, WASO wake after sleep onset.

All patients were subjected to nocturnal attended full polysomnography (PSG) (type I sleep study) (16 (link)) (SOMNOscreen TM Plus, SOMNOmedics GmbH, Germany). The PSG recording included electroencephalography (EEG), electrooculogram (EOG), electromyogram (EMG; chin and bilateral anterior tibialis), electrocardiogram (ECG), pulse oximetry, body position, airflow, and thoracic and abdominal movements using respiratory inductance plethysmography. Airflow was measured using both nasal thermistor and pressure transducer. Patients were monitored via camera throughout the study with video recording, and synchronized PSG video. The PSG studies were manually scored by one of the authors (MIM) using the American Academy of Sleep Medicine (AASM) scoring manual version 2.5 (17 (link)). Apnea hypopnea index (AHI) was calculated as the number of apneas and hypopneas per hour of sleep. The oxygen desaturation index (ODI) (number of 3% or more drops in the oxygen saturation per hour of sleep) as well as the percentage of the sleep time spent with oxygen saturation <90% (T90) were recorded. Those with an AHI > 5 events/hour with symptoms [symptoms were defined as presented in (17 (link))] or those with an AHI > 15 regardless of symptoms were considered to have OSA (17 (link)).

Overnight polysomnographic sleep recordings (PSG) were conducted in the homes of the participants with SOMNOscreen plus (SOMNOmedics GmbH, Germany). Electroencephalography (EEG) measurements were recorded with gold cup electrodes at 6 EEG locations (F3, F4, C3, C4, O1 and O2) and two derivations for the mastoids (A1, A2) according to the standardized 10/20 system. The electro-oculogram (EOG) and the electromyogram (EMG) were measured by using disposable adhesive electrodes (Ambu Neuroline 715, Ambu A/S, Denmark), two locations for EOG and three locations for EMG. In addition, an online reference Cz and a ground electrode in the middle of forehead were used. The sampling rate was 256 Hz (the hardware filters for SOMNOscreen plus are 0.2–35 Hz).
All signals were digitally offline filtered with pass band of 0.5–40 Hz (Hamming windowed sinc zero-phase FIR filter, cut-off (−6 dB) 0.25 Hz and 44.3 Hz respectively) and re-referenced to the average signal of A1 and A2 electrodes. Sleep stages from PSG data were scored manually with the DOMINO program (v2.7; SOMNOmedics GmbH, Germany) by three experienced researchers in 30-second epochs.