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

Abstract

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 α1 (i.e. slopes above and below a cross-over point). The αs and α1 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.