Acute Effect of Auricular Nerve Stimulation on Peristalsis

This study aimed to assess short-term effects of transcutaneous auricular vagus nerve stimulation (taVNS) applied to four predefined sites on the cymba conchae (CC), with the goal of modulating specific physiological functions. A secondary objective was to investigate whether taVNS could influence bowel sounds (BSs), potentially indicating alterations in gastric motility. Five healthy female volunteers, aged 21 to 23 years, participated in the study. The taVNS procedure involved the insertion of a plug equipped with four globule-shaped platinum stimulating electrodes (cathodes) into the external ear. The common anode (CA) was positioned at the nape of the neck. Physiological measurements, including BSs and cardiac activity, were obtained using phonogastrogram (PGG) and forefinger photoplethysmographic (FPPG) recordings, respectively. The acquisition of the PGG signal was based on the detection of BSs during the taVNS application to the CC. The frequency and spectral characteristics of BSs were recorded using contact microphones (MICs). To evaluate the clinically relevant effects of taVNS on the gastrointestinal tract (GIT), volunteers were interviewed before and after the intervention, and their responses to a set of questions regarding GIT-related symptoms were analyzed. The results demonstrated an overall increase in normalized amplitude across all microphones, alongside an average increase in bowel sound frequency, except at MIC3. Notably, three out of five volunteers reported a sensation of hunger following the taVNS intervention.