Table 2.
Features extracted for automated sleep staging, specifically detailing those from an electrocardiogram (ECG) signal. All electrooculogram (EOG) and electromyogram (EMG) features were detailed in a previous study (Cooray et al., 2019).
| Channel | Category | Features | Reference |
|---|---|---|---|
| ECG | Heart beat regularity | Irregular Index (IrrIndex), Origin Count, and evidence of compensatory pauses (PACEv) | (Sarkar et al., 2008) |
| ECG | R-peak intervals (RR) | Mean and median RR interval, standard deviation of the RR interval (SDNN), square root of mean of squares of difference between adjacent RR intervals (SDNN), square root of mean of squares of difference between adjacent RR intervals (RMSSD), standard deviation of differences between adjacent RR intervals (SDSD), number of pairs of adjacent RR intervals differing by more than 50 ms (NN50), and percentage NN50 (pNN50, NN50 divided by the total number of RR intervals). | (Andreotti et al., 2018) |
| ECG | Time series | Zero crossing interval (ZCI), mean zero crossing interval (mZCI), variation of amplitude (AmpVarsqi), standard deviation of amplitude (Ampstdsqi), and mean amplitude (AmpMean). | (Andreotti et al., 2018) |
| ECG | Peak frequency and power | Low frequency peak (LFpeak), high frequency peak (HFpeak), total power, low frequency power (LFpower), high frequency power (HFpower), low frequency power percentage (nLF), high frequency power percentage (nHF), and low and high frequency ratio (LFHF). All features were also calculated with a normalised value. | (Andreotti et al., 2018) |
| ECG | Non-linear | Standard deviation of Poincare plot (PoincareSD1 and PoincareSD2), sample entropy, approximate Entropy, recurrence rate, determinism (DET), Shannon entropy (ENTR), diagonal line length (L), Teager-Kaiser energy operator (TKEO), detrended fluctuation analysis exponent (DAFa2), Lempel Ziv complexity (LZ), mutual information (PD and BD), auto-correlation (BDa and PDa) | (Andreotti et al., 2018) |
| ECG | Heart beat | Tachycardia (Tachy, > 100 beats per minute (bpm) in adults) and bradycardia (Brady, < 60 bpm in adults). | (Andreotti et al., 2018) |
| NA | Elapsed time | Hours recorded from start (HoursRec) and time in hours from the end of the recording (HoursRecEnd). | (this work) |