Transcutaneous Auricular Vagus Nerve Stimulation: Comparison of Effectiveness of In-ear and Behınd-ear Stimulation

There are no generally accepted values for taVNS (transcutaneous auricular vagus nerve stimulation) application parameters (amplitude, frequency, intensity, duration, side); therefore, there are heterogeneous applications in studies. In a meta-analysis on the safety profile of taVSS, local skin irritation (18. 2%), headache (3.6%), nasopharyngitis (1.7%), dizziness (1.4%) and nausea (1.1%) were reported and taVSS treatment was reported as an effective and safe treatment with these side effects, most of which were transient and did not require additional intervention.

During taVNS, autonomic activities increase in favour of the parasympathetic system and this results in an increase in heart rate variability (HRV). Although an increase in HRV has been demonstrated by different studies, the factors that can predict the change in HRV are not clear. In a study by Geng et al. using taVSS, it was observed that HRV indicators representing vagal nerve activity increased significantly when stimulation was performed in the morning, but evening stimulation did not yield similar results. In addition, they found that improvements in measures of autonomic balance were more pronounced in the presence of lower vagal activity; they also found that by increasing the duration of stimulation, the effect of taVNS on HRV was not regulated by duration. In other words, HRV changes had the best effect only at the beginning of stimulation.