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High Fidelity MZI-BCG Sensor With Homodyne Demodulation for Unobtrusive HR and BP Monitoring

An all-optical active homodyne detection aided fiber-optic Mach-Zehnder interferometer (MZI) vital signs monitoring system is proposed and investigated. The active homodyne detection is mainly realized by employing a wavelength-tunable vertical-cavity surface-emitting laser (VCSEL) and automatic closed-loop control system (CLCS). It can effectively maintain the MZI sensor to operate around the quadrature point and successfully eliminate the fading effect of output signal induced by low frequency drift. Therefore, high fidelity and high stableness of the ballistocardiograph (BCG) signal is guaranteed. The results show that according to the Bland-Altman and the confidence ellipse analysis, the heart rate (HR) monitoring performance reveals high accuracy and good consistence. What’ more, a multiple linear regression-based blood pressure (BP) estimation model is presented, which shows that the BP is highly correlated with I-J-K complex oriented features, including IJ interval, JK interval and JK amplitude. It indeed offers a potential approach to achieve cuff-less BP estimation merely based on the high-fidelity BCG signal. In conclusion, the proposed MZI-BCG monitoring system is simple to use, and it shows great potential in future unobtrusive cardiac monitoring both in home and hospital.