Heart Variability Biofeedback as Supplementary Care for Brain Cancer: A Feasibility Study

Methods for Heart Rate Variability Biofeedback (HRVB): A Systematic Review and Guidelines

Heart Rate Variability Biofeedback (HRVB) has been widely used to improve cardiovascular health and well-being. HRVB is based on breathing at an individual's resonance frequency, which stimulates respiratory sinus arrhythmia (RSA) and the baroreflex. There is, however, no methodological consensus on how to apply HRVB, while details about the protocol used are often not well reported. Thus, the objectives of this systematic review are to describe the different HRVB protocols and detect methodological concerns. PsycINFO, CINALH, Medline and Web of Science were searched between 2000 and April 2021. Data extraction and quality assessment were based on PRISMA guidelines. A total of 143 studies were finally included from any scientific field and any type of sample. Three protocols for HRVB were found: (i) "Optimal RF" (n = 37), each participant breathes at their previously detected RF; (ii) "Individual RF" (n = 48), each participant follows a biofeedback device that shows the optimal breathing rate based on cardiovascular data in real time, and (iii) "Preset-pace RF" (n = 51), all participants breathe at the same rate rate, usually 6 breaths/minute. In addition, we found several methodological differences for applying HRVB in terms of number of weeks, duration of breathing or combination of laboratory and home sessions. Remarkably, almost 2/3 of the studies did not report enough information to replicate the HRVB protocol in terms of breathing duration, inhalation/exhalation ratio, breathing control or body position. Methodological guidelines and a checklist are proposed to enhance the methodological quality of future HRVB studies and increase the information reported.

Neuromodulation Applied to Diseases: The Case of HRV Biofeedback

The vagus or “wandering” nerve is the main branch of the parasympathetic nervous system (PNS), innervating most internal organs crucial for health. Activity of the vagus nerve can be non-invasively indexed by heart-rate variability parameters (HRV). Specific HRV parameters predict less all-cause mortality, lower risk of and better prognosis after myocardial infarctions, and better survival in cancer. A non-invasive manner for self-activating the vagus is achieved by performing a slow-paced breathing technique while receiving visual feedback of one’s HRV, called HRV-biofeedback (HRV-B). This article narratively reviews the biological mechanisms underlying the role of vagal activity and vagally mediated HRV in hypertension, diabetes, coronary heart disease (CHD), cancer, pain, and dementia. After searching the literature for HRV-B intervention studies in each condition, we report the effects of HRV-B on clinical outcomes in these health conditions, while evaluating the methodological quality of these studies. Generally, the levels of evidence for the benefits of HRV-B is high in CHD, pain, and hypertension, moderate in cancer, and poor in diabetes and dementia. Limitations and future research directions are discussed.

Symptom Management Among Cancer Survivors: Randomized Pilot Intervention Trial of Heart Rate Variability Biofeedback

Chronic cancer-related symptoms (stress, fatigue, pain, depression, insomnia) may be linked with sympathetic nervous system over-activation and autonomic imbalance. Decreased heart rate variability (HRV) is an indicator of autonomic dysregulation that is commonly observed among cancer survivors. HRV biofeedback (HRVB) training induces HRV coherence, which maximizes HRV and facilitates autonomic and cardiorespiratory homeostasis. This randomized, wait-list-controlled, pilot intervention trial tested the hypothesis that HRVB can improve HRV coherence and alleviate cancer-related symptoms. The intervention group (n = 17) received 4-6 weekly HRVB training sessions until participants demonstrated skill acquisition. Controls (n = 17) received usual care. Outcomes assessed at baseline and follow-up included 15-min HRV recordings (HRV Coherence Ratio), and symptoms of: stress, distress, post-traumatic stress disorder (PTSD), pain, depression, fatigue, and sleep disturbance. Linear mixed models for repeated measures were used to assess Group-by-Time interactions, pre- versus post-treatment differences in mean symptom scores, and group differences at follow-up. Mean HRV Coherence Ratios (± standard error) improved in the HRVB group at follow-up (baseline: 0.37 ± 0.05, post-intervention: 0.84 ± 0.18, p = 0.01), indicating intervention validity. Statistically significant Group-by-Time interactions indicated treatment-related improvements in HRV Coherence Ratios (p = 0.03, Pre-vs. post-treatment effect size [Cohen's d]: 0.98), sleep symptoms (p = 0.001, d = 1.19), and sleep-related daytime impairment (p = 0.005, d = 0.86). Relative to controls, the intervention group experienced trends toward improvements in stress, distress, fatigue, PTSD, and depression, although no other statistically significant Group-by-Time interactions were observed. This pilot intervention found that HRVB training reduced symptoms of sleep disturbance among cancer survivors. Larger-scale interventions are warranted to further evaluate the role of HRVB for managing symptoms in this population. Registration: NCT03692624 www.clinicaltrials.gov.