Auricular Ultrasonic Vagus Nerve Stimulation: Effectiveness of Blinding and Occurrence of Adverse Effects in Healthy Volunteers.

Background/objectives: Both invasive and non-invasive electrical stimulation of the vagus nerve have been studied as potential treatments for neurological conditions, with mixed results. Ultrasonic Vagus Nerve Stimulation (U-VNS), which non-invasively stimulates the auricular branch of the vagus nerve using ultrasound, may offer a more targeted and effective approach than electric currents. To facilitate future clinical trials of U-VNS, this study aimed to (1) investigate the effectiveness of blinding of a U-VNS device versus a sham device and (2) record the type, onset, and duration of any adverse effects resulting from U-VNS.

Methods: In this single-blind randomised controlled study, twenty healthy volunteers were randomly assigned to receive either a 30 min session of true U-VNS and a 30 min session of sham stimulation 1 week later, or vice versa. The effectiveness of blinding and the occurrence of adverse effects were measured using self-report questionnaires.

Results: James' Blinding Index showed that blinding using the sham device was highly effective in both the real U-VNS condition, BI = 0.9 (95% CI: 0.7-1.0), and the sham condition, BI = 1.0 (95% CI: 1.0-1.0). The adverse effects reported were mild, transient, and mostly related to sensations on the skin immediately under the transducer of the device.

Conclusions: A high level of blinding effectiveness can be achieved for U-VNS by using a sham device. Adverse effects are generally mild and transient. These findings will inform the design of future clinical trials of U-VNS.