Deep breathing (DB) is known to elicit positive changes to the heart rate variability (HRV) measurement and improve the quality of well-being. However, literature reporting on the effects of the mindful DB duration is scant. This study investigated the HRV indices and its correlation with the mental health scores of three different mindful DB durations.
Fifty participants were recruited and assigned to the control (Con, n = 13), mindful DB for 5 min (DB5, n = 14), 7 min (DB7, n = 11), or 9 min (DB9, n = 12) group. The HRV was measured during the baseline, mindful DB intervention, post-intervention, and a follow-up session after 7 days of practicing the DB daily. The mental health state was screened during the baseline and follow-up session.
During the intervention, all three DB groups had a significantly larger standard deviation of the normal-to-normal interval and normalized low frequency power whereas the normalized high frequency power (nHF) was significantly smaller than the control group. The depression score for the DB7 and DB9 participants was significantly smaller than the control group (p = 0.024 and p = 0.021, respectively). A significant negative correlation was obtained for the depression score and nHF of the DB9 group (r = − 0.673, p = 0.016).
The mindful DB duration plays a role in the shifting of the autonomic nervous system such that only the reduction in depression for the DB9 group was associated with the greater activation of the parasympathetic nervous system.