A Phonocardiographic-Based Fiber-Optic Sensor and Adaptive Filtering System for Noninvasive Continuous Fetal Heart Rate Monitoring.

Radek Martinek,Radana Kahankova,Petr Bilik,Jaromir Konecny,Homer Nazeran,Petr Janku,Stanislav Kepak,Marcel Fajkus,Jan Nedoma

doi:10.3390/s17040890

Abstract

This paper focuses on the design, realization, and verification of a novel phonocardiographic- based fiber-optic sensor and adaptive signal processing system for noninvasive continuous fetal heart rate (fHR) monitoring. Our proposed system utilizes two Mach-Zehnder interferometeric sensors. Based on the analysis of real measurement data, we developed a simplified dynamic model for the generation and distribution of heart sounds throughout the human body. Building on this signal model, we then designed, implemented, and verified our adaptive signal processing system by implementing two stochastic gradient-based algorithms: the Least Mean Square Algorithm (LMS), and the Normalized Least Mean Square (NLMS) Algorithm. With this system we were able to extract the fHR information from high quality fetal phonocardiograms (fPCGs), filtered from abdominal maternal phonocardiograms (mPCGs) by performing fPCG signal peak detection. Common signal processing methods such as linear filtering, signal subtraction, and others could not be used for this purpose as fPCG and mPCG signals share overlapping frequency spectra. The performance of the adaptive system was evaluated by using both qualitative (gynecological studies) and quantitative measures such as: Signal-to-Noise Ratio—SNR, Root Mean Square Error—RMSE, Sensitivity—S+, and Positive Predictive Value—PPV.

Highlights

Introduction17th century when these signs were considered essential to distinguish between live and dead fetuses
The monitoring of fetal heart sound by general practitioners dates back to the second half of the17th century when these signs were considered essential to distinguish between live and dead fetuses.To listen to these heart sounds, the so-called Pinard’s stethoscope or its modern versions have been in use for several decades [1,2,3]
Real raw data were acquired from a group of 10 volunteer pregnant women

Summary

Introduction

17th century when these signs were considered essential to distinguish between live and dead fetuses To listen to these heart sounds, the so-called Pinard’s stethoscope or its modern versions have been in use for several decades [1,2,3]. One of the disadvantages of this method is its high sensitivity to different types of noise generated by maternal movements, which requires frequent repositioning of the ultrasound transducers. This method does not seem suitable for long-term continuous fetal monitoring due to the potential harmful effects of ultrasonic radiation on the fetus, which are not well understood at this stage.

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