Fig 3. Diurnal variation in the sample entropy in the VLF2 subrange.

The MeanEn_VLF2 for a 4-hour period was plotted every 2 hours, where the center of the interval was assigned as the time. The blue rectangles denote the patients with incident ischemic strokes and the red rectangles denote the patients that did not develop ischemic strokes. MeanEn_VLF2: mean value of sample entropy of the very-low frequency range 2 (90–300 s).