The biobehavioural effects of respiratory rhythms on stress response

Abstract

Breathing exercises have long been documented as effective interventions for improving stress resilience. However, the optimal pace of breathing exercise for alleviating psychological and biological distress symptoms, and the mechanisms behind such effects, remained unclear. This study investigated how practising diaphragmatic slow-paced (DS) breathing at 6 breaths per minute (coincides with the intrinsic arterial blood pressure oscillation at 0.1 Hz), or diaphragmatic typical-paced (DT) breathing at 15 breaths per minute (at the typical respiratory rhythm), 20 minutes daily for 2 weeks, could modify psychological, physiological and biochemical correlates of distress symptoms compared to a natural unpaced (NU) breathing group. One hundred and six participants were recruited and randomly assigned into the DS, DT and NU groups. We found that the DS condition was effective for relieving anxiety symptoms compared to the NU condition after 2 weeks. Pulse oximetry showed that there were greater increases in low frequency heart rate variability (HRV) throughout the training period for the DS group, and greater increase in this index after 8 sessions for the DT group compared to the NU group, indicating greater autonomic modulations by the breathing exercises. For the DS and NU groups, changes in anxiety after 2 weeks of training were fully mediated by changes in low frequency HRV after 8 sessions, which suggests a causal role of the parasympathetic nervous system in the anxiolytic effect of breathing exercise. In addition, the DS and DT groups showed greater increase in very low frequency HRV compared to the NU group after 1 session and 8 sessions respectively, indicating that both the DS and DT protocols could be effective in modifying the intrinsic cardiac nervous system activity indexed by the very low frequency HRV which was positively correlated with stress resilience at baseline. Although salivary interleukin-1β changes did not significantly differ between the 3 groups, there were greater reduction in salivary cortisol for the DT condition compared to the DS condition, and significant negative correlation was observed between changes in cortisol and interleukin-1β levels for the DT condition after 1 session of training, which may imply immune-endocrine interactions associated with the breathing exercise practices. Furthermore, in the DS condition, low frequency HRV change was negatively correlated with salivary interleukin-1β change after 8 and 15 sessions, suggesting enhanced parasympathetic activity may suppress inflammation through practicing the DS breathing exercise. Taken together, our slow-paced and typical-paced breathing exercise protocols could serve as useful stress-relieving interventions for strengthening physical and mental health.