Real time processing and analysis of fetal phonocardiographic signals.

The monitoring of fetal heart rate (FHR) is commonly used in assessing the general health of the fetus. Although certain periodic cycles may be indicative of fetal problems, only short term observations are routinely employed in clinical practice. This is due to cost considerations, inconvenience to the patient and concern about long term ultrasonic monitoring. Therefore only a low confidence assessment can be established between detected rhythms and the health of the fetus. The technique advocated in this paper makes use of an inexpensive, non-invasive phonocardiographic (phono) transducer which facilitates safe long-term patient monitoring. A variable comb filter applied to the frequency domain is used in order to take full advantage of the harmonic content of fetal heart signals. Real time estimation of FHR has been achieved on pre-recorded phono signals lasting eight hours. Recordings with a reasonable signal quality were analysed and some of the results are given. Advanced signal processing techniques followed by Artificial Intelligence (AI) algorithms reduce the number of erroneous estimates during periods of low signal to noise ration (SNR). The resulting FHR time series is stored on the host computer for further processing, display and parameter extraction. This paper outlines the processing steps involved.