“Markers of benefit”: the influence of physiological and physical factors on the relationship between slow-paced breathing and heart rate variability

Abstract Purpose Slow-paced breathing (SPB) improves autonomic balance and increases heart rate variability (HRV). The influence of combat-related traumatic injury (CRTI), baseline respiratory rate (RR), and physical function/activity on the relationship between SPB and HRV has not been examined previously and was the aim of this study. Methods We analysed the first follow-up data from the ongoing ArmeD serVices trAuma rehabilitatioN outComE (ADVANCE) Cohort study. Short-term HRV was measured using a single-lead electrocardiogram during five minutes of spontaneous breathing, followed by five minutes of SPB (six breaths/minute). We examined the effect modification of SPB on HRV by CRTI (yes/no), RR during spontaneous breathing (< 15/ ≥ 15 breaths/minute), weekly moderate-to-vigorous physical activity (MVPA) using the International Physical Activity Questionnaire and physical function (6-minute-walk-distance; 6MWD). Linear models for panel data were run, adjusting for age, sampling rank, ethnicity, and cardiovascular and respiratory medication. Results A total of 962 male participants (median age: 37.6 years; n = 487 injured, n = 495 uninjured; mean 11years post-injury/deployment) with paired spontaneous-SPB HRV data were included. All short-term HRV measures increased during SPB when compared to spontaneous breathing. CRTI, 6MWD and MVPA did not significantly moderate the effect of SPB on HRV, but baseline RR ≥ 15 breaths/minute did, with Root-Mean-Square-Of-Successive-Difference (RMSSD) increasing from 15.57ms to 21.89ms ( p < 0.001) during SPB. Conclusion SPB improves HRV regardless of CRTI status. Those with higher baseline RR are more likely to obtain a significant improvement in HRV during SPB. SPB-based interventions may be introduced for the rehabilitation of military personnel following injury/deployment.