J. Saleen, A. Ball, A. Bova, K. Nelson, W. M. Silvers

Whitworth University, WA

Stimuli such as smell, sight, touch, or sounds associated with outdoor environments have been found to upregulate parasympathetic (PSNS) activity. Deep breathing (DB) has also been linked to increased PSNS activity and heart rate variability (HRV), which in turn have been associated with greater health prognoses. Therefore, it may be possible for people to listen to nature sounds as a method to increase HRV as a method to improve health. PURPOSE: The purpose of this study was to identify the effect of nature sounds on HRV. METHODS: Thirty-four healthy college-aged students, (nmale = 7, nfemale = 27, age: 20.5 ± 1.21 y, weight: 169 ± 9 kg, height: 69 ± 12 cm), completed a 10 min DB exercise in two different sessions (nature sounds and silence). Participants wore a chest strap monitor to obtain heart rate (HR) and HRV expressed as standard deviation normal to normal (SDNN), root mean square of successive differences (RMSSD), high frequency (HF) power, low frequency (LF) power, and LF/HF ratio. Noise-canceling headphones were worn during the DB exercises to minimize distractions, particularly during the silent condition. A repeated measures ANOVA (p ≤ 0.05) was used to determine significant differences between time (0 min, 5 min, and 10 min) and condition (nature and silence) for each dependent variable. RESULTS: No statistical differences were observed between nature sounds and silence for all dependent variables (p > 0.05). However, there was a statistical difference between time points for SDNN (0 to 5 min: -15.30 ± 3.34 ms, 0 to 10 min: -11.90 ± 3.21 ms, p < 0.001), HF power (0 to 5 min: 1295.32 ± 496.24 Hz, 0 to 10 min: 1063.50 ± 431.31 Hz, p = 0.012), and LF power (0 to 5 min: -3805.54 ± 913.85 Hz, 0 to 10 min: -3006.94 ± 838.89 Hz, p < 0.001) in both conditions. CONCLUSIONS: Under these research conditions, nature sounds did not improve HRV. A possible explanation for the observed results was that nature sounds may not be impactful when separated from other nature stimuli. On a different note, it was found that changes to HRV in both conditions were realized with as little as 5 min of DB, with no further change at 10 min, which indicates promise for very short acute interventions. Further research is needed to investigate the optimal effect and duration of DB or nature exposure on PSNS activity, HRV, or other health metrics.

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