ABSTRACT

INTRODUCTION. Heart rate variability biofeedback (HRV-BFB) is a widely used non-pharmacological technique based on slow, resonance-frequency breathing (~6 breaths/min), presumed to act through a specific autonomic mechanism involving baroreflex resonance and vagal afferent signaling.

AIM. To critically evaluate whether the proposed specific autonomic mechanism of HRV-BFB is supported by sham-controlled trial evidence, or whether its clinical effects are better explained by non-specific psychological factors. 

MATERIALS AND METHODS. A narrative review of the literature was conducted using PubMed, Scopus, and Google Scholar (1996–2026), focusing on randomized controlled trials with a valid sham condition, systematic reviews and meta-analyses, and neuroimaging studies of HRV-BFB.

RESULTS AND DISCUSSION. The classical baroreflex-resonance model is supported by several physiological studies (increased baroreflex gain, specificity of the individual resonance frequency). However, the small set of trials employing a valid sham condition presents a mixed picture: in one of the most methodologically rigorous trials to date (N = 47), HRV-BFB outperformed sham on affect and depression outcomes but produced no specific modulation of autonomic nervous system activity. Other sham-controlled trials (in critical illness polyneuropathy and traumatic brain injury) yield conflicting results. A comparison of individually determined resonance frequency against a fixed 0.1 Hz rate found no significant difference in clinical efficacy. 

CONCLUSION. The clinical effects of HRV-BFB are probably genuine, but current sham-controlled evidence does not unambiguously confirm the specific autonomic mechanism proposed by the classical baroreflex-resonance model. Non-specific mechanisms – prefrontal self-regulation and expectation effects – may contribute substantially. Future trials should assess psychological and autonomic outcomes simultaneously within a valid sham-controlled design.

KEYWORDS: heart rate variability, biofeedback, baroreflex, vagus nerve, reproducibility of results, placebo effect 

For citation: Es'haghi M., Safarov M.Sh. Heart Rate Variability Biofeedback: Specific Mechanism or Reproducibility Crisis? A Review. Comorbidity Neurology. 2026; 3 (3): 87–94. https://doi.org/10.62505/3034-185x-2026-3-3-87-94 

*For correspondence: Mahdis Es'haghi, Faculty of Medicine, Tver State Medical University, Tver, Russia, e-mail: mahdis.eshaghi@mail.ru.

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ADDITIONAL INFORMATION

Mahdis Es'haghi, Faculty of Medicine, Tver State Medical University, Tver, Russia. E-mail: mahdis.eshaghi@mail.ru. ORCID: https://orcid.org/0009- 0003-6853-9344.

Mirali Sh. Safarov, Phthisiologist, Regional Tuberculosis Hospital, Kaluga, Russia. E-mail: miraliduhtur@mail.ru.

Author contributions. All authors confirm their authorship according to the international ICMJE criteria (all authors contributed significantly to the conception, study design and preparation of the article, read and approved the final version before publication).

Funding. This study was not supported by any external sources of funding.

Disclosure. The authors declare no apparent or potential conflicts of interest related to the publication of this article.

The content is available under the Creative Commons Attribution 4.0 International License.
©2026, Mahdis Es'haghi, Mirali Sh. Safarov