Ballistocardiography and Seismocardiography: A Review of Recent Advances <s> B. SCG Signal Description <s> Seismocardiogram (SCG) is the recording of the minute body accelerations induced by the heart activity, and reflects mechanical aspects of heart contraction and blood ejection. So far, most of the available systems for the SCG assessment are designed to be used in a laboratory or in controlled behavioral and environmental conditions. In this paper we propose a modified version of a textile-based wearable device for the unobtrusive recording of ECG, respiration and accelerometric data (the MagIC system), to assess the 3d sternal SCG in daily life. SCG is characterized by an extremely low magnitude of the accelerations (in the order of g × 10−3), and is masked by major body accelerations induced by locomotion. Thus in daily life recordings, SCG can be measured whenever the subject is still. We observed that about 30 seconds of motionless behavior are sufficient for a stable estimate of the average SCG waveform, independently from the subject's posture. Since it is likely that during spontaneous behavior the subject may stay still for at least 30 seconds several times in a day, it is expected that the SCG could be repeatedly estimated and tracked over time through a prolonged data recording. These observations represent the first testing of the system in the assessment of SCG out of a laboratory environment, and open the possibility to perform SCG studies in a wide range of everyday conditions without interfering with the subject's activity tasks. <s> BIB001 </s> Ballistocardiography and Seismocardiography: A Review of Recent Advances <s> B. SCG Signal Description <s> Ballistocardiography was recorded in 3-D on a free floating astronaut in space as well as on healthy volunteers participating to the ESA 55th and DLR 19th parabolic flights campaigns. In this paper we demonstrate further the usefulness of recording and analyzing ballistocardiograms (BCG) in three dimensions. The spatial curves of the displacement, velocity and acceleration vectors are analyzed instead of their individual 2-D components. The maximum magnitude of the force vector is shown to be poorly correlated to the HI and IJ wave amplitude traditionally computed on the longitudinal (feet-to-head) component of acceleration (uni-dimensional BCG). We also suggest that kinetic energy and work are useful parameters to consider for a physiological interpretation of the 3D-BCG. The technique presented is invariant from the axis of representation and provides important novel physiological information. We stress further the need of 3D recordings and analysis techniques for Ballisto- and Seismo-cardiography. <s> BIB002
SCG is the measure of the thoracic vibrations produced by the heart's contraction and the ejection of blood from the ventricles into the vascular tree. Today, the SCG can readily be detected by placing a low-noise accelerometer on the chest. If a tri-axial accelerometer is used, SCG components are present in all three axes, each displaying a specific pattern BIB002 , BIB001 . However, in the literature, the majority of studies on SCG only focus on the amplitude of the dorso-ventral component, although it is likely that additional biological information could be derived also from the analysis of the longitudinal and lateral SCG components, and from the analysis of the acceleration vector trajectory during the heart cycle. Unless the contrary is stated to be consistent with the prevalent literature only the dorso-ventral acceleration component of SCG will be considered in the remainder of this paper.