Band-phase-randomized surrogate data reveal high-frequency chaos in heart rate variability

We propose a new band-phase-randomized surrogate data method to evaluate the chaotic dynamics in the high (HF) and low frequency (LF) bands of heart rate variability (HRV) in healthy subjects. The chaotic strength of normal HRV as assessed by a noise titration assay completely vanished when its power spectrum was phase-randomized over the entire frequency band or the HF band alone, but not the LF band alone. This finding confirms recent evidence that chaotic dynamics in normal HRV is ascribable mainly to the HF component, or respiratory sinus arrhythmia.