The Effect of Auditory Stimulation on the Nonlinear Dynamics of Heart Rate: The Impact of Emotional Valence and Arousal

Background: Although it is known that sound exposure evokes changes in autonomic activity, the effects of noise and music on the nonlinear behavior of heart rate fluctuations remain poorly understood and controversial. This study aims to assess the influence of sound subjective emotional valence and arousal on the nonlinear characteristics of the autonomic nervous system during passive listening. Methods: In this study, 42 subjects listened to four sounds: (1) white noise, (2) road traffic noise, (3) excitatory music, and (4) a lullaby. The experiment consisted of two consecutive sessions: 5 minutes of rest, followed by 5 minutes of listening. RR intervals were recorded during both sessions. The following linear and nonlinear heart rate variability (HRV) indices were computed: Standard deviation of NN (SDNN), The root mean square of successive differences between normal heartbeats (RMSSD), F, high frequency (HF), approximate entropy (ApEn) and sample entropy (SampEn), correlation dimension (D2), Poincaré plot indices (SD1, SD2), fractal scaling exponents (alpha1, alpha2), and recurrence plot indices (mean line length [Lmean], maximum line length [Lmax], determinism [DET], laminarity [LAM], maximal vertical length [Vmax], trapping time [TT], Shannon entropy of line length distribution [ShanEn]). Results: Excitatory music was associated with a significant decrease in SDNN (from 47.3 ± 3.59 to 38.31 ± 3.16, P < 0.01), RMSSD (from 51.07 ± 4.75 to 42.53 ± 3.9, P < 0.05), HF (from 1516.26 ± 245.74 to 884.07 ± 183.44, P < 0.001), and low frequency (LF; from 973.33 ± 176.09 to 760.28 ± 150.35, P < 0.05). Excitatory music exposure induced significant increases in DET (P < 0.01), SD1 (P < 0.05), and SD2 (P < 0.05), but changes in detrended fluctuation analysis (DFA), SampEn, and D2 were nonsignificant. Traffic noise, white noise, and the lullaby did not cause significant changes in the measures of HRV. Conclusion: Presentation of excitatory music that evokes strong negative emotions elicits a prominent decrease in respiratory sinus arrhythmia. Poincaré plot and recurrence plot measures possess high sensitivity to excitatory music. Contrary to previous studies, we did not find the effects of relaxing music on HRV