Evaluating the Impact of Heart Rate Variability Biofeedback Training on Psychological Wellbeing and Quality of Life of Female Breast Cancer Survivors: A Longitudinal Mixed Methods Randomised Controlled Trial

This thesis aimed to assess the effectiveness of heart rate variability (HRV) biofeedback training for improving chronic cancer-related symptoms commonly reported by breast cancer survivors including anxiety, insomnia and menopausal symptoms known to negatively impact on psychological wellbeing in long-term survivorship. These symptoms are associated with autonomic dysfunction and reduced heart rate variability (HRV) and currently lack effective non-pharmacological solutions. A three-armed longitudinal randomized controlled trial utilised a 4-week remote smartphone-based HRV biofeedback intervention involving daily paced breathing. Sixty female primary breast cancer survivors (between 6 – 60 months post-active treatment) were randomly assigned to intervention (6 breaths p/min), active control (12 breaths p/min) and waitlist control (no intervention) groups with 1:1:1 ratio. Outcomes were collected pre-intervention, post-intervention, and at 6 months follow-up and included quantitative and qualitative measures. Quantitative measures included resting baseline HRV, self-reported psychological and physical symptoms, stress reactivity (assessed with a modified Trier Social Stress Test), cognitive flexibility (assessed using a computer-based Task-Switching paradigm). Qualitative outcomes included 1-hour semi-structured audio-recorded interviews for forty-four participants from across groups exploring symptom changes, intervention experience and effects across time and analysed using Thematic analysis. The intervention group showed significant increases in resting low-frequency HRV over time and reported long-lasting improvement in stress-sleep-vasomotor symptom cluster and showed more adaptive stress reactivity post-intervention compared to active and waitlist controls. Qualitative findings also revealed that the intervention strongly boosted self-regulation capacity with lasting behavioural effects and long-lasting improvements in quality of life. Active control participants reported weaker improvements in self-regulation without comparable impact on quality of life. Waitlist group reported no symptom changes across time. Overall, the findings of this work demonstrate that HRV biofeedback can be a feasible non-pharmacological tool for improving psychological wellbeing and quality of life in breast cancer survivors, with strong implications for holistic cancer-related symptom management.