Extraction of the aortic and pulmonary components of the second heart sound using a nonlinear transient chirp signal model

The objective of this paper is to adapt and validate a nonlinear transient chirp signal modeling approach for the analysis and synthesis of overlappin g aortic (A(2)) and pulmonary (P-2) components of the second heart sound (S -2), The approach is based on the time-frequency representation of multicom ponent signals for estimating and reconstructing the instantaneous phase an d amplitude functions of each component. To evaluate the accuracy of the ap proach, a simulated S-2 with A(2) and P-2 components having different overl apping intervals (5-30 ms) was synthesized. The simulation results show tha t the technique is very effective for extracting the two components, even i n the presence of noise (-15 dB). The normalized root-mean-squared error be tween the original A(2) and P-2 components and their reconstructed versions varied between 1% and 6%, proportionally to the duration of the overlappin g interval, and it increased by less than 2% in the presence of noise. The validated technique was then applied to S-2 components recorded in pigs und er normal or high pulmonary artery pressures. The results show that this ap proach can successfully isolate and extract overlapping A(2) and P-2 compon ents from successive S-2 recordings obtained from different heartbeats of t he same animal as well from different animals.