Effect of the Airway Pressure on the Frequency Domain of Seismocardiographic Signal

Seismocardiography (SCG) is cardiac-induced chest wall vibration that is often measured non-invasively by accelerometers [1, 2]. SCG is thought to be related to myocardial contractions, valve closures and changes in blood momentum during the cardiac cycle [2–5]. SCG was also reported to assess myocardial contractility [6] and detect valvular heart diseases (e.g., aortic valve stenosis [7]), which would be clinically valuable. The intrathoracic pressure variation during respiration could affect cardiac dynamics and possibly SCG. For example, during inspiration, the low intrathoracic pressure increases the right venous return and right ventricle (RV) preload (i.e., the force that stretches the cardiac muscle prior to contraction) [8] which in turn decreases the left ventricular (LV) preload. This LV preload reduction was attributed to a leftward shift of the interventricular septum that limits LV filling [8]. Besides, during inspiration, the LV afterload was reported to increase due to the increase of the aortic transmural pressure [8]. The frequency domain description of SCG may contain information about blood ejection into the great vessels (in the 0.6-20 Hz band) and heart sounds (for frequencies > 20 Hz) [5]. The objective of the current study is to investigate the effect of the intrathoracic pressure variation on SCG spectral characteristics. This may also increase the understanding of SCG variability.