Detection of S1 and S2 locations in phonocardiogram signals using zero frequency filter

Heart auscultation is a widely used technique for diagnosing cardiac abnormalities. In that context, capturing of phonocardiogram (PCG) signals and automatically monitoring of the heart by identifying S1 and S2 complexes is an emerging field. One of the first steps involved for identifying S1-S2 complexes is detection of the locations of these events in the PCG signals. Methods proposed in literature, to detect these events in the PCG signal, have largely focused on exploiting the dominant low frequency characteristics of the S1-S2 complexes through frequency--domain processing. In this paper, we propose a purely time--domain processing based method that employs a heavily decaying low pass filter (referred to as zero frequency filter) to suppress extraneous factors and detect S1-S2 locations. We demonstrate the potential of the proposed approach through investigations on two publicly available data sets, namely the PASCAL heart sounds challenge 2011 (PHSC-2011) and PhysioNet CinC. The method is also evaluated through an analysis with wearable sensors in the presence and absence of speech activity.