Ballistocardiography and Seismocardiography: A Review of Recent Advances <s> A. BCG Signal Description <s> BACKGROUND ::: We measured the three-dimensional ballistocardiogram (BCG) in a free-floating subject in sustained microgravity during spaceflight to test the usefulness of such measurements for future non-invasive monitoring of cardiac function, and to examine the effects of respiratory movement on the BCG in three axes. ::: ::: ::: METHODS ::: Acceleration was measured using a three-axis accelerometer fastened to the lumbar region of the subject while simultaneous recordings of ECG, and respiratory motion via impedance plethysmography were also made. Data were recorded during a 146-s period of inactivity on the part of the subject during which time there was no contact with the spacecraft. ::: ::: ::: RESULTS ::: Total body motion due to respiratory activity was consistent with that calculated from the known action of the diaphragm and conservation of momentum. The accelerations due to cardiac activity, ensemble averaged over the R-R interval, were greatest along the head-to-foot axis. Maximum amplitude of the HIJK complex of the BCG generated by ventricular ejection was greatest in the head to foot axis (approximately 70 x 10(-3) m x s(-2)), but there were also substantial accelerations along the dorsoventral axis of up to 43 10(-3) m x s(-2), that are not measured interrestrial two-dimensional studies. The amplitude of the BCG was strongly affected by lung volume, with accelerations being reduced 50 to 70% between end-inspiration and end-expiration. ::: ::: ::: CONCLUSIONS ::: These data suggest a greatly reduced transmission of the cardiac motion to the body at end-expiration (FRC) than at higher lung volumes. The BCG might be further developed as a non-invasive means of monitoring parameters such as stroke volume in microgravity. <s> BIB001 </s> Ballistocardiography and Seismocardiography: A Review of Recent Advances <s> A. BCG Signal Description <s> The ballistocardiogram (BCG) signal represents the movements of the body in response to cardiac ejection of blood. The BCG signal can change considerably under various physiological states; however, little information exists in literature describing how these forces are generated. A physical analysis is presented using a finite element model of thoracic aortic vasculature to quantify forces generated by the blood flow during the cardiac cycle. The traction at the fluid-solid interface of this deformable wall model generates a Central Aortic Force (CAF) which appears of similar magnitude to recorded BCG forces. The increased pulse pressure in an exercise simulation caused a significant increase in CAF, which is consistent with recent BCG measurements in exercise recovery. <s> BIB002 </s> Ballistocardiography and Seismocardiography: A Review of Recent Advances <s> A. BCG 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> BIB003
At every heartbeat, the blood travelling along the vascular tree produces changes in the body center of mass. Body micromovements are then produced by the recoil forces to maintain the overall momentum. The BCG is the recording of these movements, can be measured as a displacement, velocity, or acceleration signal, and is known to include movements in all three axes. The longitudinal BCG is a measure of the head-to-foot deflections of the body, while the transverse BCG represents anteroposterior (or dorso-ventral) vibrations. The original bed-and table-based BCG systems focused on longitudinal BCG measurements, representing what was supposed to be the largest projection of the 3-D forces resulting from cardiac ejection  . Table I summarizes modern BCG measurement systems and their axes of measurement. Note that for some systems, head-to-foot and dorso-ventral forces are unavoidably, mixed together in the measurement, and this should be accounted for when interpreting results. However, in spite of the 3-D nature of the BCG, for a long period of time only the microdisplacements 2168-2194 © 2014 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications standards/publications/rights/index.html for more information. Head-to-foot -Posture affects signal quality and repeatability -Motion artifacts must be detected and mitigated of the body along the longitudinal axis (head-to-foot) were considered. Currently, BCG is mainly measured using a force plate or force sensor placed on a weighing scale or under the seat of a chair, with the subject in a vertical position. Modern approaches to BCG measurement are discussed below in Section III. It should be considered, however, that the gravity force and any contact of the body with external objects, including the floor and measuring devices, somewhat interferes with, or even impedes, the body displacement induced by the recoil forces. As a result, the BCG measurement on earth is always affected by some distortion. The ideal environment for assessing the BCG would be in microgravity settings, such as during space missions. Such experiments have been performed, and the results described below confirm that in microgravity the whole body recoil forces (BCG) are significant in all three dimensions   BIB001 BIB003 . Modeling studies examining the cardiogenic traction forces of the aorta have confirmed this finding as well BIB002 .