Dynamics of heart rate variability during and after exposure to the sounds of tibetan singing bowl sounds in university students

Purpose. To investigate phase-related changes in heart rate variability (HRV) during and after exposure to Tibetan singing bowl sounds and to determine whether these changes differed according to baseline autonomic profiles and sound protocols. Materials & Methods. The study included 61 university students (mean age 20.1±2.20 years; 47 women and 14 men) in a within-subject crossover design with repeated measurements. R-R intervals were recorded using a Polar H10 chest-strap sensor and the Research HRV application. Seven HRV indices were analysed: Mean R-R, SDNN, RMSSD, log-transformed Baevsky stress index (log(SI)), SD2/SD1, Sample Entropy, and DFAα1. Linear mixed-effects models were used to assess Profile, Phase, Protocol, and their interactions. P-values were adjusted using the Benjamini-Hochberg false discovery rate procedure. Results. Significant main effects of Phase were observed for Mean R-R, SDNN, RMSSD, log(SI), SD2/SD1, and DFAα1 (all pBH-FDR <0.001), but not for Sample Entropy. No significant main effect of Protocol was identified for any HRV index (all pBH-FDR ≥0.778). Significant Profile × Phase interactions were found for Mean R-R, SDNN, RMSSD, and log(SI) (all pBH-FDR ≤0.009), indicating that phase-related changes differed according to baseline autonomic profile. However, neither Protocol × Phase nor Profile × Protocol × Phase interactions were statistically significant. Conclusions. The findings demonstrate significant phase-related changes in cardiac autonomic regulation during the experimental procedure. However, the absence of protocol-specific interactions provides no evidence that the different Tibetan singing bowl sound protocols produced distinct phase-dependent HRV responses.