Higuchi Fractal Dimension Applied to RR Intervals During Exposure to Musical Auditory Stimulation

Several musical genres have been demonstrated to encourage changes in cardiac autonomic modulation. So, we aimed to investigate the acute effects of auditory stimulation with heavy metal music by applying the Higuchi fractal dimension algorithm. The study was performed in 19 healthy women aged between 18 and 30 years old. HRV was analysed during two time phases: the 20-minute period without exposure to music and the 20-minute during exposure to the heavy metal music. The subjects were exposed to one equivalent sound level (approx. 80dB) for 20 minutes. We did not observe significant responses of heart rate and RR intervals — heavy metal musical auditory stimulation decreased the Higuchi fractal dimension median value from 1.9533 (control) to 1.9204 (musical stimulation). In conclusion, the heavy metal music stimulation has been revealed to reduce the complexity of the HRV signal through cardiac autonomic modulation. J Physiol Pharmacol 2017; 61(3) : 211–218 *Corresponding author : Vitor Engrácia Valenti, Departamento de Fonoaudiologia – Faculdade de Filosofia e Ciências, FFC/UNESP, Avenida HyginoMuzzi Filho, 737. CEP: 17525-900. Marília, SP, Brazil; Ph.: +55 (14) 3402-1300; E-mail: [email protected] (Received on March 12, 2017) Introduction Heart rate variability (HRV) describes the oscillations of the intervals between consecutive heart beats (RR intervals) that are linked to the influences of the autonomic nervous system (ANS) on the sinus node (1). 212 Nogueira, Garner, Vanderlei, Abreu and Valenti Indian J Physiol Pharmacol 2017; 61(3) of HRV during musical exposure are rare in the research literature. In 1988 Higuchi proposed a new algorithm for computing the fractal dimension of discrete time sequences (12). It is applied directly to the time-series. As the reconstruction of the attractor phase space is unnecessary, the algorithm is simpler and faster than correlation dimension (D2) and many other classical measures adapted from chaos theory. In this sense, we examined the effects of auditory stimulation with music on HRV through analysis of Higuchi fractal dimension (13-15) applied to RR intervals during exposure to musical auditory stimulation. Previously an analogous computation, correlation dimension (D2) (15-18) had been applied in some situations but is computationally slower since the reconstruction of the attractor phase space is necessary. Such calculations have previously proven significant in additional areas of study including Schizophrenia, (19) Parkinson’s disease, (20) epilepsy, (21) depression, (22) or Creutzfeldt-Jakob disease (23).