Source separation of foetal heart sounds and maternal activity from single-channel phongrams: A temporal independent component analysis approach

Jimenez-Gonzalez, A. and James, C.J. (2008) Source separation of foetal heart sounds and maternal activity from single-channel phongrams: A temporal independent component analysis approach. 35th Annual Conference of Computers in Cardiology, Bologna, Italy. 13 - 16 Sep 2008.

Abstract

We propose a method for extracting sources from noisy single-channel abdominal phonograms such as foetal heart sounds (FHS) and maternal activity. Three single-channel abdominal phonograms, between 3 and 5 minutes in length, were used. The recordings were obtained from pregnant women with foetal gestation ages between 36 and 40 weeks using a piezoelectric transducer. The abdominal ECG was recorded simultaneously using a sampling frequency of 500 Hz. These phonograms are processed as follows: first, the single-channel phonogram is projected into a higher dimension by constructing and appropriate matrix of delays. Next, multiple independent components are calculated using a standard implementation of Independent Component Analysis. After that, these components are projected back onto the measurement space to be finally classified (according to their spectral similarity) to recover the sources contained in the phonogram. Results show successful extraction of FHS, maternal activity, line noise and some unidentified sources (probably speech and/or digestive activity). Moreover, even though it is virtually impossible to distinguish the FHS in the phonograms, their extraction looks quite good in two subjects, where S1 and S2 are evident while only S1 is visible in the third subject. The method also extracted maternal activity, composed of the respiration and/or the pulse wave sources (present from time to time with an unpredictable contribution), in all subjects. This extraction was not necessarily as separate sources such as respiration and pulse wave, but importantly isolated from the FHS. Considering the foetal and maternal activities in more detail, it is important to point out the high performance of the method extracting them as separate sources. Thus, this extraction is especially significant because the maternal pulse wave may overlap the FHS in the same way the maternal QRS overlaps the foetal QRS in the abdominal ECG. The most outstanding factor is that this separation is achieved by using a single-channel method. So, this single-channel approach extracts physiological sources from the abdominal phonogram, and we believe it will be useful for surveillance, not only on foetal well-being, but also for maternal condition. (Abstract Control Number: 238)

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