Effects of auricular electrical stimulation on vagal activity in healthy men: evidence from a three-armed randomized trial

The activity of the VN (vagus nerve) is negatively associated with risk factors such as stress and smoking, morbidity and mortality. In contrast, it is also a target of therapeutic intervention. VN stimulation is used in depression and epilepsy. Because of its high invasivity and exclusive application to therapy-resistant patients, there is interest in less invasive methods affecting the VN. Several studies examining acupuncture report beneficial effects on vagal activity. However, findings are inconsistent, and applied methods are heterogeneous resulting in difficulties in interpretation. The purpose of the present study was evaluation of the effects of acupuncture on vagal activity in a three-armed randomized trial while controlling several disturbing factors. Fourteen healthy men participated in random order in four examinations: a control condition without intervention, a condition with placebo, manual acupuncture and electroacupuncture. Acupuncture was conducted on the concha of the ear, as there is neuroanatomical evidence for vagal afferents. Each examination took place once, with a week's time between examinations. RSA(TR) (respiratory sinus arrhythmia adjusted for tidal volume) indicating vagal activity was measured continuously. The study was conducted partially blind in accordance with recommendations. After controlling for respiration, condition-specific pain sensation, individual differences in belief of acupuncture effectiveness and time effects not attributable to the interventions, electroacupuncture but not manual acupuncture was found to have a positive effect on RSA(TR). The results underline the potential role of auricular electrical stimulation to induce an increase in vagal activity, and it therefore might be used as preventive or adjuvant therapeutic intervention promoting health.