Heart rate variability biofeedback in adults with chronic spinal cord injury: a randomised feasibility study

BACKGROUND: Heart rate variability biofeedback (HRV-F) is a neurocardiac self-regulation therapy, that has been shown to improve cardiac autonomic regulation, emotional regulation, and cognitive function in various clinical populations. Despite this, there is little evidence for the benefit of HRV-F in adults with spinal cord injury (SCI). METHODS: This study evaluated the feasibility of conducting a parallel randomised controlled trial (RCT) to evaluate the effectiveness of a 10-week HRV-F intervention for adults with chronic SCI. Individuals with SCI (irrespective of level and completeness), at least 12 months after diagnosis due to any traumatic or non-traumatic and non-progressive cause, and aged between 18 and 70 years of age were eligible to participate. Feasibility was evaluated in terms of six primary outcomes: (i) randomisation and blinding, (ii) participant safety, (iii) recruitment, (iv) retention, (v) adherence to the intervention, and (vi) primary outcome data collection methods (heart rate variability [HRV] and cerebral blood velocity [CBv]). Participants' satisfaction, impression of change, and technological issues were assessed as secondary outcomes. RESULTS: The first 10 participants of the RCT (n = 120) were studied in the 10-week feasibility study. No serious adverse events occurred during the study activities (assessment or intervention sessions). While there were no withdrawals and high adherence to the intervention, the recruitment rate was below the target. There were no missing HRV data; however, missing data for CBv was higher than anticipated based on the literature (35% vs. 20%). A few minor connectivity issues occurred with the technology used for home training by participants. Modifications to the RCT protocol, including adjusting the eligibility criteria, recalculating the sample size, conducting interventions in participants' homes, and altering the CBv assessment protocol, were proposed to address these issues. CONCLUSIONS: With the proposed modifications implemented, the RCT is deemed feasible for investigating the effectiveness of a 10-week HRV-F intervention for adults with chronic SCI. TRIAL REGISTRATION: Australian and New Zealand Clinical Trial Registry (ACTRN12621000870853). Registered on July 6, 2021.