Among the plethora of indices that can describe the fractal-like behaviour of heart rate variability (HRV), the fractal dimension (FD) and the power-law exponent () have gained wide acceptance. Since HRV is generally modelled with fractional Brownian motion (fBm), the linear scaling relationship between and FD, valid for fBm, is often applied to HRV series to derive one index from the other. In this paper the relationship between and FD is calculated in normal (NR) and heart failure (HF) HRV series. Results revealed that a linear dependence between and FD can be found only when the slope of the spectral density is calculated over the whole spectrum instead of considering more widespread very low frequency ranges. Moreover, the relationship is slightly different from that characterizing fBm and is not unique for the two categories of subjects. The common practice of estimating from FD for HRV applying the theoretical relationship should be reconsidered.

Non-linear parameters obtained from heart rate variability (HRV) analysis has recently been recognized to provide valuable information for physiological interpretation of heart rate fluctuation. Among the numerous non-linear parameters related to the fractal behaviour of the HRV signal, two classes have gained wide interest in the last years: the beta exponent based on the 1/f-like relationship, starting from the spectral power, and that based on fractal dimension. In order to evaluate the relationship between lesion's severity and fractal behaviour, 20 first-ever stroke subjects and 10 healthy subjects were studied. Patients were divided in two groups according to single or multiple medium cerebral artery lesions. All subjects underwent 24-hour Holter recording analysed by fractal and 1/f-like techniques. Differently from methods usually used in literature to evaluate the fractal dimension (FD), in this work the FD was extracted by using the Higuchi's algorithm that permits...

We evaluated the effects of the PCM on the fractal analysis of the HRV in healthy women. We evaluated healthy women between 18 and 30 years old. HRV was analyzed in the time (SDNN, RMSSD, NN50 and pNN50) and frequency (LF, HF and LF/HF ratio) domains as well as short and long-term fractal exponents (alpha-1 and alpha-2) of the detrended fluctuation analysis (DFA). HRV was recorded at rest for ten minutes at seated rest and then the women quickly stood up from a seated position in up to three seconds and remained standing for 15 minutes. HRV was recorded at the following time: rest, 0-5 min, 5-10 min and 10-15 min during standing. We observed decrease (p < 0.05) in the time-domain indices of HRV between seated and 10-15 minutes after the volunteer stood up. The LF (ms(2)) and HF (ms(2)) indices were also reduced (p < 0.05) at 10-15 minutes after the volunteer stood up compared to seated while the LF (nu) was increased at 5-10 min and 10-15 min (p < 0.05). The short-term alph...