Non-Invasive Transcutaneous Auricular Vagus Nerve Stimulation Applied at Different Durations in Healthy Adults

Overview

This randomized, participant-blinded, sham-controlled interventional study aims to compare the acute effects of non-invasive transcutaneous auricular vagus nerve stimulation (taVNS) applied at different durations on autonomic nervous system responses in healthy adults. Participants will be assigned to either an active taVNS group or a sham stimulation group. Within each group, participants will complete three separate study visits in which stimulation will be applied for 5, 10, and 15 minutes in randomized order, with 48- to 72-hour washout intervals between visits. Heart rate variability, heart rate, blood pressure, respiratory rate, and subjective discomfort will be assessed immediately before and after each intervention session. The study is designed to determine whether the acute autonomic effects of taVNS vary according to stimulation duration and whether a duration-related response pattern can be identified.

Transcutaneous auricular vagus nerve stimulation (taVNS) is a non-invasive neuromodulation method in which electrical stimulation is applied to auricular regions innervated by the auricular branch of the vagus nerve. Because of its low-risk profile, non-surgical application, and potential autonomic regulatory effects, taVNS has attracted increasing interest in autonomic physiology and cardiovascular research. Previous studies in healthy individuals suggest that taVNS may influence autonomic balance, particularly through changes in heart rate variability (HRV), heart rate, and related physiological parameters. However, substantial heterogeneity remains across published taVNS studies with regard to stimulation parameters such as frequency, pulse width, current intensity, and intervention duration. Among these parameters, stimulation duration is one of the least standardized, and sham-controlled comparisons of different application durations remain limited. This study is designed to investigate whether the acute autonomic effects of taVNS differ according to stimulation duration. The study uses a randomized, participant-blinded, sham-controlled mixed design. Healthy adults aged 18 to 40 years will be randomized to either an active taVNS group or a sham stimulation group. Participants will remain in their assigned group throughout the study. Within each group, each participant will attend three separate visits and receive stimulation for 5, 10, and 15 minutes in randomized order. Visits will be separated by 48- to 72-hour washout intervals. Active taVNS will be applied bilaterally to the cymba conchae region using non-invasive stimulation parameters consistent with the study protocol. Sham stimulation will be delivered under visually and procedurally similar conditions to minimize expectancy effects. Before and immediately after each intervention session, autonomic and physiological outcomes will be assessed, including heart rate variability derived from RR interval recordings, heart rate, systolic and diastolic blood pressure, respiratory rate, and subjective discomfort measured by a visual analog scale. The primary objective is to compare the acute autonomic responses to active taVNS and sham stimulation across different stimulation durations. The study also aims to explore whether a duration-response relationship exists for autonomic outcomes in healthy adults. Findings from this trial may help inform duration selection in future experimental and clinical taVNS research.