Noninvasive Transcutaneous Auricular Vagal Nerve Stimulation Improves Gastric Slow Waves Impaired by Cold Stress in Healthy Subjects

Background/Aims: Stress is known to inhibit gastric motility. The aim of this study was to investigate the effects and autonomic mechanisms of transcutaneous auricular vagal nerve stimulation (taVNS) on cold stress (CS)-induced impairment in gastric motility that are relevant to the brain-gut interactions in healthy volunteers. Materials and Methods: Healthy volunteers (eight women; age 28.2 +/- 1.8 years) were studied in four randomized sessions (control, CS, CS + taVNS, and CS + sham-electrical stimulation [sham-ES]). Each session was composed of 30 minutes in the fasting state and 30 minutes after a standard test meal. CS was induced during minutes 10 to 30 after the meal, whereas taVNS or shamES was performed during minutes 0 to 30 after the meal. The electrogastrogram and electrocardiogram were recorded for assessing gastric slow waves and autonomic functions, respectively.Results: First, CS decreased the percentage of normal gastric slow waves (59.7% +/- 9.8% vs 85.4% +/- 4.5%, p < 0.001 vs control); this impairment was dramatically improved by taVNS (75.5% +/- 6.3% vs 58.4% +/- 12.5%, p < 0.001 vs sham-ES). Second, CS increased the symptom score (22.0 +/- 12.1 vs 39.3 +/- 11.5, p = 0.001 vs control); taVNS, but not sham-ES, reduced the symptom score (26.0 +/- 12.2 vs 38.3 +/- 21.6, p = 0.026 vs sham-ES). Third, CS decreased vagal activity assessed from the spectral analysis of heart rate variability (0.21 +/- 0.10 vs 0.26 +/- 0.11, p < 0.05 vs control) and increased the sympathovagal ratio (4.89 +/- 1.94 vs 3.74 +/- 1.32, p = 0.048 vs control); taVNS normalized CS-induced suppression in vagal activity (0.27 +/- 0.13 vs 0.22 +/- 0.10, p = 0.049 vs sham-ES; p > 0.05 vs control) and CSinduced increase in the sympathovagal ratio (3.28 +/- 1.61 vs 4.28 +/- 2.10, p = 0.042 vs sham-ES; p > 0.05 vs control).Conclusion: The noninvasive taVNS improves the CS-induced impairment in gastric pace-making activity, possibly by reversing the detrimental effect of CS on autonomic functions. taVNS may have a therapeutic potential for stress-induced gastric dysmotility.