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.
Aged 18-40 years.
Healthy volunteers.
Able to perform spirometry and follow study instructions.
Provided written informed consent.
Any cardiovascular disease, cardiac arrhythmia, hypertension, or related condition.
Any neurological disorder (e.g., diabetes mellitus, peripheral neuropathy, epilepsy).
Any diagnosed psychiatric disorder.
Any respiratory disease (e.g., asthma, chronic obstructive pulmonary disease).
Parallel
Transcutaneous auricular vagus nerve stimulation
DeviceTranscutaneous auricular vagus nerve stimulation is delivered bilaterally using an external stimulator with electrodes placed on auricular regions targeted for vagal innervation (e.g., cymba conchae). Stimulation is applied for approximately 10 minutes. Parameters are standardized (e.g., 25 Hz; pulse width 200-300 microseconds), and current intensity is individually adjusted to a clearly perceptible but non-painful level. The procedure is performed in a single visit with pre- and post-intervention spirometry and physiological monitoring as specified in the protocol.
Sham transcutaneous auricular stimulation
DeviceSham stimulation uses the same device, setup, and session duration to mimic the active procedure. Electrodes are placed on an ear location intended to minimize vagal activation (e.g., ear lobule), and stimulation is delivered at a minimal/low level to provide a similar sensation without therapeutic vagal stimulation. Pre- and post-session spirometry and other measurements are collected identically to the active arm.
Change in forced expiratory volume in 1 second (FEV1)
Forced expiratory volume in 1 second (FEV1), reported in liters (L), will be measured immediately before and immediately after the intervention. The outcome will be defined as the pre-to-post change (post minus pre), and between-group differences in change between active stimulation and sham control will be evaluated.\[FVC\], and peak expiratory flow \[PEF\]) will be measured immediately before and immediately after the intervention. The primary endpoint is the pre-to-post change (post minus pre) and the between-group difference in change between active stimulation and sham control.
Change in forced vital capacity (FVC)
Forced vital capacity (FVC), reported in liters (L), will be measured immediately before and immediately after the intervention. The outcome will be defined as the pre-to-post change (post minus pre), and between-group differences in change between active stimulation and sham control will be evaluated.
Change in peak expiratory flow (PEF)
Peak expiratory flow (PEF), reported in liters per minute (L/min), will be measured immediately before and immediately after the intervention. The outcome will be defined as the pre-to-post change (post minus pre), and between-group differences in change between active stimulation and sham control will be evaluated.
Change in RMSSD from chest recordings
Heart rate variability will be recorded from chest-based beat-to-beat intervals before and after the intervention in a standardized resting condition. The root mean square of successive differences (RMSSD), reported in milliseconds (ms), will be derived from these recordings. The endpoint is the pre-to-post change (post minus pre) and the between-group difference in change between active bilateral stimulation and sham control.
Change in SDNN from chest recordings
Heart rate variability will be recorded from chest-based beat-to-beat intervals before and after the intervention in a standardized resting condition. The standard deviation of normal-to-normal intervals (SDNN), reported in milliseconds (ms), will be derived from these recordings. The endpoint is the pre-to-post change (post minus pre) and the between-group difference in change between active bilateral stimulation and sham control.
Change in LF power from chest recordings
Heart rate variability will be recorded from chest-based beat-to-beat intervals before and after the intervention in a standardized resting condition. Low-frequency (LF) power, reported in milliseconds squared (ms²), will be derived from these recordings. The endpoint is the pre-to-post change (post minus pre) and the between-group difference in change between active bilateral stimulation and sham control.
Change in HF power from chest recordings
Heart rate variability will be recorded from chest-based beat-to-beat intervals before and after the intervention in a standardized resting condition. High-frequency (HF) power, reported in milliseconds squared (ms²), will be derived from these recordings. The endpoint is the pre-to-post change (post minus pre) and the between-group difference in change between active bilateral stimulation and sham control.
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