Flexible Electronic Sensor for Noncontact Simultaneous Measurement of Capacitive Skin Sympathetic Nerve Activity (cSKNA) and cECG

Noncontact electrocardiogram (ECG) sensors have been widely explored as unobtrusive, long-term solutions for detecting atrial fibrillation (AF). Recent clinical studies have demonstrated that abnormal activation of the autonomic nervous system plays a crucial role in the pathogenesis of AF, highlighting the importance of coordination between autonomic activity and cardiac electrophysiology, which shifts most standalone ECG-based AF detection toward AF prediction. In this study, we present a flexible electronic sensor with a bandwidth of 0.05-1000 Hz, utilizing capacitive coupling to enable noncontact simultaneous measurement of capacitive SKNA (cSKNA) and capacitive ECG (cECG) signals. The flexible design ensures effective signal capture by conforming to body curvature, enhancing capacitive coupling. Human measurements involving cold pressor tests (CPTs) were conducted to validate the cSKNA and cECG functionality and applicability of the proposed sensor under various fabric conditions, including different humidity levels, thicknesses, and materials. Moreover, human trials demonstrated the sensor's capability to simultaneously capture cSKNA and cECG signals, effectively revealing neuro-cardiac interactions in real-time. Notably, during CPT-induced sympathetic nerve activation interventions, increases in measured cSKNA that exceeded the sympathetic burst threshold were associated with heart rate (HR) acceleration derived from the measured cECG signals, effectively demonstrating the sensor's capability in capturing neuro-cardiac responses. In conclusion, the proposed sensor offers a noncontact unobtrusive sensing solution for monitoring neuro-cardiac interactions, providing new insights for establishing predictive AF models through a more convenient and comfortable sensing system without electrode preparation. Its ease of use and versatility make the sensor suitable for potential applications in wearable chest bands and smart beds in the future.