Ballistocardiography and Seismocardiography: A Review of Recent Advances <s> C. BCG and SCG Waveforms <s> The ballistocardiogram (BCG) measures the reaction of the body to cardiac ejection forces, and is an effective, non-invasive means of evaluating cardiovascular function. A simple, robust method is presented for acquiring high-quality, repeatable BCG signals from a modified, commercially available scale. The measured BCG waveforms for all subjects qualitatively matched values in the existing literature and physiologic expectations in terms of timing and IJ amplitude. Additionally, the BCG IJ amplitude was shown to be correlated with diastolic filling time for a subject with premature atrial contractions, demonstrating the sensitivity of the apparatus to beat-by-beat hemodynamic changes. The signal-to-noise ratio (SNR) of the BCG was estimated using two methods, and the average SNR over all subjects was greater than 12 for both estimates. The BCG measurement was shown to be repeatable over 50 recordings taken from the same subject over a three week period. This approach could allow patients at home to monitor trends in cardiovascular health. <s> BIB001 </s> Ballistocardiography and Seismocardiography: A Review of Recent Advances <s> C. BCG and SCG Waveforms <s> The ballistocardiogram (BCG) signal represents the movements of the body in response to cardiac ejection of blood. Recently, many groups have developed low-cost instrumentation for facilitating BCG measurement in the home. The standard method used in the literature for estimating the BCG pulse response has generally been ensemble averaging over several beats. Unfortunately, since the BCG pulse response is likely longer than a typical heartbeat interval, this standard approach does not yield a full-length estimate of the response. This paper describes a simple, novel algorithm for estimating the full-length BCG pulse response using the R-wave timing of a simultaneously acquired electrocardiogram (ECG). With this pulse response, the full signal can be reconstructed, enabling the analysis of slow transient effects in the BCG signal, and of the measurement noise. Additionally, while this paper focuses only on the BCG signal, the same algorithm could be applied to other biomedical signals such as the phonocardiogram or impedance cardiogram, particularly when the heartbeat interval is shorter than the duration of the cpulse response. <s> BIB002
For each heart contraction, a BCG and SCG waveform is generated. Each waveform is characterized by several peaks and valleys reflecting specific events of the beating heart. Fig. 1 shows a typical ECG, head-to-foot BCG, tri-axial SCG, impedance cardiogram (ICG), and arterial blood pressure (ABP) measurement from a healthy subject (data were collected with approval from the Institutional Review Board, IRB, at the Georgia Institute of Technology, and with written informed consent obtained). A high-resolution, miniature accelerometer was used for the SCG data collection (356A32, PCB Piezotronics, Depew, NY, USA), and a modified weighing scale was used for the BCG recording as described previously in BIB001 . The ECG and ICG waveforms were measured using the BN-RSPEC and BN-NICO wireless units (BIOPAC Systems, Inc., Goleta, CA, USA) interfaced to the MP150WSW data acquisition hardware (BIOPAC Systems, Inc., Goleta, CA, USA). The ABP was measured from the finger using the A2SYS Nexfin Monitor (Edwards Lifesciences, Irvine, CA, USA). For this measurement, z corresponded to the dorso-ventral, y to the head-to-foot, and x to the right-to-left lateral components of the SCG. The labels of the peaks and valleys of the dorso-ventral components shown in this figure are according to  ,  ; for the BCG, the labels are according to  . For the SCG, the labels correspond to the physiological event they are believed to represent: MC, mitral valve closure; IVC, isovolumetric contraction; AO, aortic valve opening; RE, rapid ejection; AC, aortic valve closure; MO, mitral valve opening; and RF, rapid filling. For the BCG, the labels of the waves are not associated directly with underlying events, but rather the current understanding is that the waveform represents the combined mechanical pulse response of the vasculature and body to cardiac ejection of blood BIB002 . Note that, when the BCG is measured by a scale or force plate, the SCG and BCG units are not the same; the SCG records the accelerations of the chest wall, and is thus presented in units of milli-g (mg); the BCG represents the displacements of the center of mass of the subject on the weighing scale, which are then converted to units of force by the spring constant for the scale platform, and thus it is presented in units of Newtons. The mass that is accelerated for the SCG is not the same as the mass accelerated for the BCG; as such, the direct conversion of the BCG to acceleration units or the SCG to force units has not yet been elucidated.