Wearable Bioimpedance Sensor Characterization for Blood Flow Monitoring

Bioimpedance is a powerful wearable sensing modality for continuous and non-invasive human deep tissue monitoring. When bioimpedance sensors are placed on the human body aligned with the underlying arteries – such as radial, ulnar, and digital – the impedance measurements show variations based on the changes in the artery dimensions due to the presence of blood pressure pulse waves. These variations can be leveraged to extract complex cardiovascular information, such as blood pressure. However, the level of impedance variations due to volumetric changes in the arteries is minimal (in the order of tens of mOhms) compared to the overall tissue impedances (in the order of hundreds of Ohms) requiring careful bioimpedance circuit and system design. In this paper, we provide comprehensive analyses of the bioimpedance sensor design requirements for arterial blood flow monitoring through numerical calculations, spice simulations, and experimental measurements. We provide analyses on signal-to-noise ratio (SNR) and effective number of bits (ENOB) requirements, indicating an 86dB SNR and 14-bit ENOB for high-resolution sensing. We believe this paper will further motivate the adoption of the promising wearable bioimpedance technology for applications of precision medicine.

生物阻抗是一种强大的可穿戴传感模式，可用于对人体深部组织进行连续且无创的监测。当生物阻抗传感器放置在人体上与下方动脉（如桡动脉、尺动脉和指动脉）对齐时，由于血压脉搏波的存在，动脉尺寸发生变化，阻抗测量值也会随之变化。这些变化可用于提取复杂的心血管信息，比如血压。然而，与整体组织阻抗（数百欧姆量级）相比，由于动脉体积变化引起的阻抗变化幅度很小（数十毫欧姆量级），这就需要精心设计生物阻抗电路和系统。在本文中，我们通过数值计算、SPICE模拟和实验测量，对用于动脉血流监测的生物阻抗传感器设计要求进行了全面分析。我们对信噪比（SNR）和有效位数（ENOB）要求进行了分析，结果表明高分辨率传感需要86dB的信噪比和14位的有效位数。我们相信本文将进一步推动有前景的可穿戴生物阻抗技术在精准医疗应用中的采用。