The Effect of Short-Term Transcutaneous Electrical Stimulation of the Auricular Vagus Nerve on Parameters of Heart-Rate Variability

Relevance. Previous studies have shown that transcutaneous vagus nerve stimulation (tVNS) can have a therapeutic effect similar to its invasive counterpart. However, an objective assessment of tVNS requires a reliable biomarker of successful vagus nerve activation.
The purpose of our study was to study the effect of short-term noninvasive stimulation of the auricular branch of the vagus nerve on heart-rate variability (HRV) parameters.
Methods. Patients were randomized into two groups according to the 1:1 scheme. Active tVNS was performed attached to the tragus of the left ear. Sham tVNS - was performed attached to the earlobe of the left ear. The stimulation frequency was 20 Hz with a pulse duration of 200 microseconds. The research algorithm included four five-minute time intervals for recording biological signals: (1) initially at rest, (2) during the first 5 minutes of stimulation, (3) during the next 5 minutes of stimulation, and (4) after the end of stimulation. HRV parameters evaluated in this study included the standard temporal and spectral characteristics of HRV. This clinical trial is registered with the ClinicalTrials database under a unique identifier: NCT05680337.
Results. A total of 111 patients were included in the study: 53- Active tVNS, 58- Sham tVNS. Initially, there were no differences in HRV parameters in the groups. After the start of stimulation, the parameters pNN50, NN50, RMSSD, VLF%, IC1, IC2, VLF%, HF%, and HF began to differ significantly in the groups. After the end of the stimulation, it was found that the RMSSD and HF% parameters became significantly lower in the Active tVNS group, and LF/HF became significantly higher than in the Sham tVNS group.
Conclusions. After the start of tVNS, there is a decrease in the levels of HRV parameters, reflecting the activity of the parasympathetic nervous system in the Active tVNS group. At the same time, there are no statistically significant dynamics in the Sham tVNS group.