A Wearable Wireless Capacitive Pressure Sensing System for Monitoring of Arteriovenous Fistula Thrill

Arteriovenous fistula (AVF) dysfunction is a leading cause of morbidity in hemodialysis patients, necessitating continuous and objective monitoring of vascular access status. Current clinical surveillance relies heavily on subjective physical examinations or intermittent imaging, lacking the capability for convenient, quantitative at-home monitoring. In this study, we present a lightweight, wearable, wireless capacitive pressure sensing system for objectively measuring AVF thrill, which is closely associated with healthy vascular access function. The system features a flexible capacitive pressure sensor (FCPS) employing a micro-grooved polydimethylsiloxane (PDMS) dielectric layer and a foldable flexible printed circuit (FPC) electrode stack with electromagnetic shielding. To ensure high signal fidelity, a 24-bit capacitance-to-digital converter (CDC) is integrated directly at the sensing interface, effectively suppressing parasitic noise. The sensor demonstrates a high sensitivity of 0.35 kPa^-1 in the sub-kPa range (<1 kPa) and a rapid millisecond-level dynamic response, enabling precise capture of subtle vascular vibrations. A compact Bluetooth Low Energy (BLE) controller transmits data to a smartphone application for real-time visualization and logging. In-vivo validation on hemodialysis patients and one healthy control subject reveals that functioning AVFs exhibit a distinct high-frequency spectral component (>7.0 Hz), a feature that is absent in normal radial pulses. By quantifying these thrill-related vibrations, the proposed system offers a promising solution for non-invasive, continuous monitoring of AVF health, potentially enabling early detection of access failure.