Fig. 3

Detection of sleep onset by HRV during polysomnography in a healthy male subject. From top: hypnogram, body motion (BM) by actigraphy, R-R interval (RRI), power spectral density (PSD), and relative power of HF to the integrated width (ω) of the frequency band around the HF peak. When the sleep stage changes from wakefulness (W) to NREM (N1, N2, N3), the large BM disappears, a sharp peak appears in the HF band (0.15‑0.4 Hz) of the RRI power spectrum, and the Hsi (area under the curve) increases to more than 70%. Modified Fig. 2 of reference [51]