Transcutaneous Auricular Vagus Nerve Stimulation and Spirometry: Sham-Controlled Randomized Trial

Transcutaneous auricular vagus nerve stimulation (taVNS) is a non-invasive neuromodulation approach delivered through the external ear. The auricular branch of the vagus nerve provides an accessible peripheral route that may influence autonomic regulation and, through autonomic-respiratory interactions, potentially affect respiratory function. Although taVNS has been investigated across several physiological domains, evidence regarding its acute effects on spirometric outcomes in healthy individuals remains limited. This study is designed to evaluate whether a single, brief session of bilateral taVNS produces measurable short-term changes in standard spirometric parameters compared with a sham procedure. This is a sham-controlled, randomized, single-blind, parallel-group trial conducted in healthy volunteers. Participants are allocated to either active bilateral taVNS or sham stimulation using a predefined randomization procedure and concealed assignment. To minimize expectancy effects, participants are blinded to group allocation, and active and sham procedures use the same device appearance and session structure. Active stimulation is delivered via electrodes positioned on auricular regions targeted for vagal innervation, whereas sham stimulation uses an alternative placement intended to minimize vagal activation while maintaining a similar sensory experience. Stimulation parameters are standardized across participants, with intensity individually titrated to a clearly perceptible but non-painful level. The primary outcomes are acute pre-to-post changes in spirometric measures obtained using standardized spirometry procedures. Key spirometric endpoints include forced vital capacity (FVC), forced expiratory volume in one second (FEV1), and peak expiratory flow (PEF). Secondary physiological measures may include heart rate, heart rate variability indices, and blood pressure to characterize autonomic and hemodynamic responses and to support safety monitoring during the session. All measurements are collected within the same visit, with spirometry performed immediately before and after the stimulation procedure following consistent instructions and quality criteria. Data analysis will focus on between-group comparisons of change scores (post minus pre) for spirometric outcomes. Depending on distributional assumptions, analyses will use appropriate parametric or non-parametric methods; when relevant, models adjusting for baseline values will be applied (e.g., ANCOVA with baseline spirometry as a covariate). Effect sizes and confidence intervals will be reported to support interpretability. Safety will be monitored throughout the visit; stimulation will be discontinued if a participant experiences significant discomfort or requests stopping. The study involves minimal risk. Expected adverse effects are transient and mild (e.g., localized tingling or mild discomfort at the ear). Rarely, lightheadedness may occur; participants will be monitored and the procedure stopped if necessary. Data will be stored in a coded/de-identified format and reported at the group level.