Time-frequency analysis of the first and the second heartbeat sounds

This paper present the analysis and comparisons of the spectrogram, Wigner distribution and wavelet transform techniques to the phonocardiogram signal (PCG). An analysis on the first (S1) and the second cardiac sounds (S2) of the normal phonocardiogram signal is considered here to be able to distinguish the various techniques in their aptitude to separate and present suitably the internal components of these sounds (S1 and S2). A comparison between these methods has shown the resolution differences between them. It is found that the spectrogram short-time Fourier transform (STFT), cannot perfectly detect the two internals components of the first sound (M1 and T1: mitral and tricuspid component respectively) and also the two internals components of the second sound S2 (A2 and P2: atrial and pulmonary component respectively). The Wigner distribution (WD) can provide time-frequency characteristics of the sounds S I and S2, but with insufficient diagnostic information: the two components, M1 and T1 for the sound S1 and the components A2 and P2 for the sound S2 and P2 are not accurately detected and seem to be one component only. It is found that the wavelet transform (WT) is capable of detecting the two internals components for each sound S1 and S2. However, the standard Fourier transform can display these internals components in frequency but not the time delay between them. Furthermore, the wavelet transform provides more features and characteristics of the sounds that will hemp physicians to obtain qualitative and quantitative measurements of the time-frequency characteristics. (c) 2006 Elsevier Inc. All rights reserved.