  Seismocardiography (SCG) offers a potential non-invasive method for cardiac
monitoring. Quantification of the effects of different physiological conditions
on SCG can lead to enhanced understanding of SCG genesis, and may explain how
some cardiac pathologies may affect SCG morphology. In this study, the effect
of the respiration on the SCG signal morphology is investigated. SCG, ECG, and
respiratory flow rate signals were measured simultaneously in 7 healthy
subjects. Results showed that SCG events tended to have two slightly different
morphologies. The respiratory flow rate and lung volume information were used
to group the SCG events into inspiratory/expiratory groups or low/high
lung-volume groups, respectively. Although respiratory flow information could
separate similar SCG events into two different groups, the lung volume
information provided better grouping of similar SCGs. This suggests that
variations in SCG morphology may be due, at least in part, to changes in the
intrathoracic pressure or heart location since those parameters correlates more
with lung volume than respiratory flow. Categorizing SCG events into different
groups containing similar events allows more accurate estimation of SCG
features, and better signal characterization, and classification.
