Design and evaluation of an autonomic nerve monitoring system based on skin sympathetic nerve activity

Abstract

The autonomic nervous system is closely related to cardiovascular diseases (CVDs). Simultaneous non-invasive recording of skin sympathetic nerve activity (SKNA) and electrocardiogram (ECG) is a new method for autonomic nervous system real-time assessment. This study presented a portable monitoring system based on SKNA. A system-level modification by combining a commercial analog front end (AFE) chip with a low-noise first-stage amplifier was implemented to reduce the system noise floor without a high-cost customized chip. An adaptive power-line-interference (PLI) filter and outliers clipping were developed to reject the PLI and motion artifacts in the signal. The laboratory experiment and clinical experiment were conducted to verify the performance and effectiveness of the proposed system. The laboratory results show that the proposed AFE has a much lower noise floor with 0.1 μVrms than the reference systems (PowerLab system). Moreover, the correlation coefficient of the envelope of SKNA (eSKNA) is 0.83, and the correlation coefficient of the heart rate variability (HRV) index is 0.99, suggesting a good performance in signal recording. The clinical results show that the proposed system can reflect sympathetic nerve activity significantly before and after anesthesia injection (p < 0.01), indicating its better feasibility in this application scenario than HRV-based devices (p = 0.40). The system achieves a comparable performance to the reference system and satisfactory performance for the autonomic nervous system assessment in clinical application.