Changes in fractal structure of heart rate variability during a nap in one case

The objective of the present study was to analyze fractal structures of adult heart rate (HR) variability during a nap. Fractal analysis was carried out in one case over consecutive 10‐min time series of HR, which were simultaneously recorded with electroencephalogram. Scaling relationships showed cross‐over patterns characterized by αs and αl (i.e. slopes above and below a cross‐over point). The αs and αl were black and white noise at Stage 4 of NREM sleep, and black and 1/f noise in REM sleep. Cross‐over points changed from the first to second sleep cycle. We demonstrate the multifractal structures of HR variability during a nap in the present case.