Chronic Venous Function Monitoring via a highly Flexible Capacitive Strain Sensing Device

Chronic venous insufficiency (CVI) is a prevalent lower limb condition among elderly and sedentary individuals, commonly manifested by ankle edema, varicose veins, and superficial venous reflux. Conventional diagnostic techniques, such as palpation and Doppler ultrasound, offer limited quantification and are unsuitable for continuous monitoring. In this study, we present a wearable monitoring system embedded within smart socks, employing flexible capacitive stretch sensors to enable real-time measurement of ankle circumference and dynamic assessment of venous function. A custom-designed capacitance sensing circuit based on an operational amplifier was developed, emphasizing miniaturization, low noise, and extended battery life. The system demonstrated excellent performance, with a linearity of 0.9994, a drift rate of 5.72×10^⁻3 %/min, and a signal-to-noise ratio (SNR) of 74.77 dB. Clinical validation involving active ankle dorsiflexion confirmed the system’s ability to accurately track dynamic changes and consistently compute ejection fraction (EF)—a key indicator of venous return—with a coefficient of variation (CV) of 0.011. These results highlight the system’s potential as a reliable, high-precision tool for early detection and ongoing management of CVI in everyday settings. © 2025 IEEE.