Kristen Sparrow • September 12, 2021
Keywords: Bayesian statistics; heart rate variability; meta-analysis; tVNS; transcutaneous auricular vagus nerve stimulation. In this study, there was no evidence of TAVNS affecting the vagally mediated component of HRV. Researchers believe, however, that TAVNS does more to inhibit sympathetic activity than increase vagal activity, so TAVNS still might have benefit in improving autonomic balance.
This study is looking at a type of analysis that can incorporate new data on an ongoing basis to answer clinical/scientific questions. In this case, the question was whether Transcutaneous Auricular Vagal Nerve Stimulation (TAVNS) affected the vagal component of HRV. In this study, there was no evidence of TAVNS affecting this component of HRV.
In my recent poster project presented last week at the International Neuromodulation Society conference in Paris, I pointed out that experts on TAVNS are of the opinion that TAVNS does more to inhibit sympathetic activity, than stimulate vagal activity. As a result it still can result in an improvement in autonomic balance, at least theoretically.
Non-invasive brain stimulation techniques, such as transcutaneous auricular vagus nerve stimulation (taVNS), have considerable potential for clinical use. Beneficial effects of taVNS have been demonstrated on symptoms in patients with mental or neurological disorders as well as transdiagnostic dimensions, including mood and motivation. However, since taVNS research is still an emerging field, the underlying neurophysiological processes are not yet fully understood, and the replicability of findings on biomarkers of taVNS effects has been questioned. The objective of this analysis was to synthesize the current evidence concerning the effects of taVNS on vagally mediated heart rate variability (vmHRV), a candidate biomarker that has, so far, received most attention in the field. We performed a living Bayesian random effects meta-analysis. To keep the synthesis of evidence transparent and up to date as new studies are being published, we developed a Shiny web app that regularly incorporates new results and enables users to modify study selection criteria to evaluate the robustness of the inference across potential confounds. Our analysis focuses on 16 single-blind studies comparing taVNS versus sham in healthy participants. The meta-analysis provides strong evidence for the null hypothesis (g = 0.014, CIshortest = [-0.103, 0.132], BF01 = 24.678), indicating that acute taVNS does not alter vmHRV compared to sham. To conclude, there is no support for the hypothesis that vmHRV is a robust biomarker for acute taVNS. By increasing transparency and timeliness, the concept of living meta-analyses can lead to transformational benefits in emerging fields such as non-invasive brain stimulation.
Keywords: Bayesian statistics; heart rate variability; meta-analysis; tVNS; transcutaneous auricular vagus nerve stimulation.