A Comparison of Infrasonic and Audio Components in the Seismocardiogram

In an earlier study, based on ECHO, we showed that the opening of the aorta valve happens before the peak in the SCG that many authors have associated with this event. Within the audible band of the acceleration signal a transient event is often seen during the S1 sound, possibly coinciding with aorta opening. Data were available from 44 normal subjects. We manually analyzed the S1 complex in the SCG in two frequency bands: 1–25 Hz (LF) and 40–400 Hz (HF) and annotated mitral valve closure in both frequency bands, the main peak in the LF SCG as fiducial point for aorta opening, and the start of the transient in the HF sound as a hypothesized indicator for aorta opening. The estimated timing of the mitral valve closure in the HF band was 1.6 ms earlier than in the LF band (sd = 5.8 ms). The estimated timing of aorta opening was 12.6 ms (sd = 9.4 ms) earlier in the HF. Thus, the estimated isovolumetric contraction time was 39 versus 50 ms. The estimated mitral valve closures in the LF and HF bands of the SCG were almost identical, whereas there was a clinically significant difference between the estimations of the aorta openings. The latter agrees with our earlier work where SCG and ECHO were compared. The true origin of the high frequency transient in the audible frequency band is still open for discussion.