Seismocardiogram Records Pressure of the Heart Ventricles on the Ribs

Abstract

Seismocardiogram (SCG) is the recording of the vibrations created by the heart beating and blood circulating in the aorta using an accelerometer placed on the sternum. It is shown that specific peaks of SCG signal coincides with major cardiac events such as mitral valve closing and aortic valve opening. However, our knowledge of SCG so far has been limited to the empirical data, and the origin of SCG signal morphology is still unclear.
A better understanding of the cardiac mechanisms underlying SCG morphology will assist us to extract hemodynamic information from the signal. The goal of this study is to demonstrate that SCG captures changes of the pressure of the beating ventricles on the ribs. 

In this study SCG was simulated by using 3D multi-scale anatomically-accurate finite element model of the canine ventricles connected to the time-varying elastance models of the atria and the model of the circulatory system. Ribs and lungs were represented as solid cylinders that were placed next to the right ventricular apex and the heart posterior wall, respectively, according to the position of the heart observed from previously published cine-MRI videos. SCG was simulated as the second temporal derivative of the heart surface pressure on the rib cylinders.

Simulated signal had major peaks of SCG which correspond to isovolumic phase of contraction. Amplitude and morphology of the signal depend on the initial position of the cylinders and confirms the inter-subject variations observed from our experimental recordings of SCG over more than three hundred subjects. 

Conclusion: SCG reflects changes of the ventricular wall pressure on the ribs during cardiac cycle.