A robust method to estimate time split in second heart sound using instantaneous frequency analysis

Closure of the aortic valve (A2) and the pulmonary valve (P2) generates the second heart sound (S2). The time separation between A2 and P2 is known as the A2-P2 split and it has very important diagnostic potential. Methods proposed in the past to measure the split noninvasively are limited either by prior signal modeling assumptions or by reliance on manual processing in key steps. In this work, we propose a new method that is devised to noninvasively provide an automated measurement of the time split between A2 and P2 with minimal prior assumptions on signal models. Our method is based on tracking the changes of the instantaneous frequency (IF) of S2 via time frequency representation of the S2 obtained by smoothed Wigner-Ville Distribution. The cues provided by the changes in the IF trajectory are analyzed using an automated procedure to identify the onset of the P2 pulse. Simulations are carried out to demonstrate the effectiveness of the procedure in estimating the split. The performance of the method in the presence of noise varying between 6 dB and 8 dB for several trials and interference is investigated and the robustness of the method is demonstrated.