Automated extraction of aortic and pulmonary components of the second heart sound for the estimation of pulmonary artery pressure

The second heart sound, S2, is generally believed to be comprised of aortic (A2) and pulmonary (P2) components. Previously, the normalized splitting interval (NSI) between the A2 and P2 components has been shown to be proportional to the pulmonary artery pressure (PAP). A set of fully automated algorithms based on adaptive modeling of A2/P2 components using chirplets were developed to provide real-time estimates of PAP. The method was tested on 16 pigs which were administered drugs to induce pulmonary hypertension. Simultaneous reference pressure measurements were obtained with a pulmonary artery catheter (PAC). Estimation of PAP in pigs using the new techniques resulted in a correlation coefficient (r) of 0.84 and standard error (SEE) of 9.2 mm Hg. This is in line with echocardiography studies, which have a performance ranging from r=0.69-0.91 and SEE from 5 to 12 mm Hg when compared to PAC measurements. It is also consistent with previous results based on a manual estimation of PAP derived through image processing methods. Based on these findings, this method has the potential to offer continuous noninvasive monitoring of PAP.