Stephen A. Zahorian
Zongyao Zhou
Charles Brewton
Dept. of Elec. Eng., Old Dominion Univ., Norfolk, VA 23529
Acoustic methods for monitoring fetal heart rate are potentially advantageous over ultrasound methods, since, eventually, long-term low-cost monitoring would be possible for high risk mothers, with no concern for fetal damage due to the monitoring device. However, sensor design and signal processing requirements are very demanding in this low signal-to-noise ratio environment. The present approach is patterned after that by Zuckewar et al. [IEEE Trans. Biomed. Eng. 40-9, 963--969 (1993)] using a third-generation sensor belt, and enhanced signal processing strategies. In the new method, each of seven differential sensor signals is scanned continuously and processed in parallel with a PC-hosted DSP system. The processing of each channel includes FIR bandpass filtering, Teager energy calculations, autocorrelation, and ``intelligent'' peak picking. ``Candidates'' for fetal heart rate are computed every 0.5 s and evaluated with a figure of merit which incorporates both measures of peak quality and continuity constraints. Clinical testing indicates that the new method of signal processing is able to reliably track fetal heart rate for most fetuses with a gestation age of at least 30 weeks. The multiple-channel approach results in a significant improvement over a single-channel method.