Effects of transcranial direct current stimulation on heart rate variability: a systematic review protocol

Objective: This systematic review aims to synthesize the available evidence on the effects of transcranial direct current stimulation on heart rate modulation, indexed by heart rate variability parameters in healthy individuals and those with clinical disorders. Introduction: There is some evidence that altered heart rate variability parameters are associated with different clinical disorders. For example, diminished parasympathetic activity has been explored as a potential biomarker for some chronic pain conditions. Considering the dynamic interaction between brain and heart, neuromodulatory strategies targeting this relationship could exert a positive influence on the cardiac autonomic system. Transcranial direct current stimulation is a non-invasive neuromodulation technique that has been presenting recent advances in the treatment of various clinical disorders. However, the evidence concerning transcranial direct current stimulation application focusing on brain-heart interaction is still controversial. Inclusion criteria: This review will consider studies that investigate the effects of transcranial direct current stimulation on heart rate variability in healthy participants or those with clinical disorders. Methods: This review will follow JBI systematic review methodology recommendations. PubMed, Embase, CINAHL, Web of Science, PsycNET, Cochrane Controlled Register of Trials (CENTRAL) and Physiotherapy Evidence Database (PEDro) will be searched, along with several sources of gray literature. Retrieval of full-text studies, and assessment of methodological quality and data extraction, will be performed independently by two reviewers. Data will be pooled in statistical meta-analysis, where possible. Systematic review registration number: PROSPERO CRD42018114105.