A preliminary study investigating the quantification of beat-to-beat in seismocardiogram signals

Ballistocardiography and seismocardiography are both non-invasive mechanical measurements of the vibrations of the body in response to the heartbeat. The ballistocardiogram (BCG) signal represents the movements of the whole body in response to cardiac ejection of blood into the vasculature; the seismocardiogram (SCG) corresponds to local vibrations of the chest wall associated with sub-audible tissue and blood movement and audio frequency heart-valve closure dynamics. This paper focuses on methods for quantifying "signal consistency"--a quantitative measure of how morphologically similar each heartbeat in a patient's recording is compared to the ensemble average taken over the recording. Before comparing each beat to the average, known physiological sources of inconsistency--such as respiratory amplitude and timing variability--are removed, then the remaining inconsistency is quantified. Previously described methods for BCG signals are expanded to fit the high-frequency (> 20 Hz) components of the SCG. The use of this method in future work could help enable proactive management of heart disease in extra-clinical settings.