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

This study will examine the short-term effects of transcutaneous auricular vagus nerve stimulation (a non-invasive electrical stimulation delivered through the outer ear) on lung function measured by spirometry in healthy adults. The vagus nerve is involved in many automatic body functions, and ear-based stimulation has been used in research to explore its possible effects on different physiological systems. However, it is not clear whether a brief stimulation session can acutely influence breathing test results in people without respiratory disease. Healthy volunteers aged 18-40 will take part in one laboratory visit. Participants will be randomly assigned to one of two groups: (1) active bilateral stimulation applied to specific ear regions that are known to be innervated by the vagus nerve, or (2) sham stimulation using the same device setup but designed to minimize vagal activation. The stimulation session will last approximately 10 minutes. Before and after the stimulation, participants will perform standard spirometry (breathing) tests. Primary spirometric outcomes will include common measures of lung function such as forced vital capacity (FVC), forced expiratory volume in one second (FEV1), and peak expiratory flow (PEF). Heart rate, heart rate variability, and blood pressure may also be recorded to monitor physiological responses and safety during the visit. Participation is voluntary and participants may withdraw at any time. The procedure is considered minimal risk. Possible side effects are usually mild and temporary, such as tingling, warmth, or mild discomfort at the ear. Rarely, participants may feel lightheaded; if this occurs, the procedure will be stopped and the participant will be monitored until symptoms resolve. There is no guaranteed direct benefit to participants. The results may help clarify whether short-term ear-based vagus nerve stimulation can influence spirometric parameters and may inform future studies on autonomic and respiratory interactions.