Closed-Loop Movement-Paired Transcutaneous Auricular Vagus Nerve Stimulation for Upper-Limb Rehabilitation: a Feasibility Study

Vagus nerve stimulation (VNS) paired with physical rehabilitation has shown promise for improving upper-limb function after neurological injury. In this study, we introduce SmartVNS, a wearable system that automatically delivers movement-paired transcutaneous auricular VNS using a wrist-worn intertial measurement unit (IMU) for accurate functional movement detection. We evaluated feasibility, usability and performance of the SmartVNS system in a four-week, 20-session clinical feasibility study involving nine individuals with stroke or spinal cord injury during conventional therapy. Despite a wide range of baseline upper-limb function in patients (ARAT scores 0-52), the system adapted to individual abilities and demonstrated a consistent stimulation rate between sessions and patients, averaging 14.7 stimulations/min with a low variability (SD = 3.4 stimulations/min; n=9). The IMU-based movement detection algorithm achieved stimulation precision comparable to therapist manual triggering (precision as mean \((\pm)\) SEM: SmartVNS: 76.3 \((\pm)\) 3.1%, therapists: 82.4 \((\pm)\) 2.6%, video analysis used a ground truth), while delivering stimulation in double the number of movements (sensitivity as mean \((\pm)\) SEM: SmartVNS: 50.4 \((\pm)\) 5.0%, therapists: 23.4 \((\pm)\) 4.7%, video analysis used a ground truth). The system demonstrated high usability (patients and therapists rated UMUX: 85 \((\pm)\) 12%) and was well-tolerated by participants, with patients able to self-apply the device. Exploratory clinical outcomes showed consistent functional improvements across participants. These findings support the feasibility and usability of SmartVNS as a scalable neuromodulation platform to support neurorehabilitation.