Fig. 4From: Assessment of autonomic function by long-term heart rate variability: beyond the classical framework of LF and HF measurementsAll-night hypnogram and Hsi in a healthy female subject (age, 28 years). While Hsi is below 70% during wake (W) and REM sleep (marked with black in hypnogram), it exceeds 70% in synchrony with the appearance of NREM sleep (N1, N2, and N3)Back to article page