Nonlinear analysis of musical lung sounds using the bicoherence index

A nonlinear analysis of musical lung sounds based on the bicoherence index is presented in this paper. The detection of quadratic phase coupling between any frequency components of musical lung sounds, by means of third-order statistics and spectra, provides a measure of their nonlinear interaction. This harmonic analysis was conducted on pre-classified signals (wheezes, ronchi, striders) selected from international teaching tapes. The derived results have shown a high degree of deviation from Gaussianity along with quadratic self-coupling within the distinct frequencies of the corresponding power spectrum of musical lung sounds. Differences in the degree of phase coupling, the nonlinearity and non Gaussianity of the processed signals, establish a new field in characterization and feature extraction of the pulmonary pathology associated with musical lung sounds.