Ballistocardiography and Seismocardiography: A Review of Recent Advances <s> B. Weighing Scale BCG <s> BACKGROUND ::: Weight gain is used by disease-management programs as a marker of heart failure decompensation, but little information is available to quantify the relationship between weight change in patients with heart failure and the risk for imminent hospitalization. ::: ::: ::: METHODS AND RESULTS ::: We conducted a nested case-control study among patients with heart failure referred to a home monitoring system by managed care organizations. We matched 134 case patients with heart failure hospitalization to 134 control patients without heart failure hospitalization on the basis of age, sex, duration of home monitoring, heart failure severity, and baseline body weight. Compared with control patients, case patients experienced gradual weight gain beginning approximately 30 days before hospitalization; changes in daily weight between case and control patients were statistically significant (P<0.001). Within the week before hospitalization, when weight patterns in case and control patients began to diverge more substantially, mean increases of more than 2 and up to 5 pounds, more than 5 and up to 10 pounds, and more than 10 pounds (relative to time of enrollment in the monitoring system) were associated with matched adjusted odds ratios for heart failure hospitalization of 2.77 (95% confidence interval 1.13 to 6.80), 4.46 (95% confidence interval 1.45 to 13.75), and 7.65 (95% confidence interval 2.22 to 26.39), respectively, compared with mean increases of 2 pounds or less. ::: ::: ::: CONCLUSIONS ::: Increases in body weight are associated with hospitalization for heart failure and begin at least 1 week before admission. Daily information about patients' body weight identifies a high-risk period during which interventions to avert decompensated heart failure that necessitates hospitalization may be beneficial. <s> BIB001 </s> Ballistocardiography and Seismocardiography: A Review of Recent Advances <s> B. Weighing Scale BCG <s> We propose a novel technique for beat-to-beat heart rate detection based on the ballistocardiographic (BCG) force signal from a subject standing on a common electronic weighing scale. The detection relies on sensing force variations related to the blood acceleration in the aorta, works even if wearing footwear and does not require any sensors attached to the body because it uses the load cells in the scale. We have devised an approach to estimate the sensitivity and frequency response of three commercial weighing scales to assess their capability to detect the BCG force signal. Static sensitivities ranged from 490 nV V(-1) N(-1) to 1670 nV V(-1) N(-1). The frequency response depended on the subject's mass but it was broad enough for heart rate estimation. We have designed an electronic pulse detection system based on off-the-shelf integrated circuits to sense heart-beat-related force variations of about 0.24 N. The signal-to-noise ratio of the main peaks of the force signal detected was higher than 30 dB. A Bland-Altman plot was used to compare the RR time intervals estimated from the ECG and BCG force signals for 17 volunteers. The error was +/-21 ms, which makes the proposed technique suitable for short-term monitoring of the heart rate. <s> BIB002 </s> Ballistocardiography and Seismocardiography: A Review of Recent Advances <s> B. Weighing Scale BCG <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> BIB003 </s> Ballistocardiography and Seismocardiography: A Review of Recent Advances <s> B. Weighing Scale BCG <s> In this study, we developed a novel technique for estimating non-constrained and cuffless blood pressure (BP) that was based on electrocardiogram (ECG) and ballistocardiogram (BCG). The BCG was non-invasively measured using a common electronic weighing scale when a subject was standing on it. The ECG was measured using three different methods: on the chest using Ag/AgCl electrodes, on the hands using dry electrodes and on the feet also using dry electrodes. For a BP correlated parameter, a time interval parameter, which was defined as the time difference between the ECG R-peak and BCG J-peak, was employed for evaluating and estimating beat-to-beat BP. Under a BP varying experiment with a Valsalva manoeuvre, the R-J intervals were extracted at every beat cycle and a systolic blood pressure (SBP) estimation equation was established using linear regression analysis for each subject. In the case of feet delivered ECG (F-ECG), an ensemble average technique synchronized at the BCG J-peak point was applied to extract the ECG signal from the feet. The performance of the proposed method was evaluated using Finapres, a non-invasive blood pressure measurement system, as a reference BP signal, and a scatter plot was used to find the regression line between the reference values and estimated BPs. A moving-window averaging technique was applied to remove the high-frequency noise in the R-J intervals and was applied to enhance the accuracy of the SBP estimation. For all individuals, the estimated SBP was similar to the measured SBP with a reliable correlation, which makes the proposed method suitable for use in a home healthcare system to monitor blood pressure on a weighing scale at the same time as measuring weight. <s> BIB004 </s> Ballistocardiography and Seismocardiography: A Review of Recent Advances <s> B. Weighing Scale BCG <s> There is a growing interest on measuring time intervals between the J peak of the ballistocardiogram (BCG) and several features of other cardiovascular signals such as the ECG in order to obtain cardiovascular function markers. Nevertheless, possible uncertainty factors involved in these measurements have not been ::: identified and analyzed, which is a necessary step to advance towards standardization in this reemerging ::: biomedical engineering field. In this paper we analyze the effect of the low-pass cutoff frequency and phase characteristic of filters, noise and power line interference on J-peak time measurement. We conclude that BCG acquisition systems require a minimum low-pass cutoff frequency of 25 Hz but the phase angle of filters at this frequency introduce more than 6 ms delay that increases with increasing filter order. Further, SNR and power line interference levels respectively below about 25 dB and 30 dB, commonly found in data acquisition systems in this area, may lead to uncertainties in the time position of the J peak of tens of milliseconds, which are ::: comparable to measured time interval changes that may have diagnostic interest. <s> BIB005
The first measurement of BCG on an electronic scale was demonstrated in 1990 by Jim Williams of Linear Technology, as described in his application note AN-43  . Williams built an elegant circuit capable of measuring bodyweight with tremendous accuracy-4.5 g resolution up to 136 kg-and found motion artifacts, and the BCG as the largest sources of noise for his measurements. The main advantage with weighing-scale-based BCG measurement is that the subject is standing up for the measurementironically, this is also the main disadvantage. While the standing posture of the subject is ideal for ensuring that the measurement is purely longitudinal, it also means the measurements are susceptible to motion artifacts and floor vibrations. This also places a practical limit on the duration of the measurements, as the patient will likely only stand still on the scale for 30-60 s at a time at most. Another key advantage of these systems is that they leverage the tremendous popularity of weighing scales, with more than 80% of American households owning a scale, and multiple companies developing new and improved "smart" scales with enhanced capabilities. The scale is also used by heart failure patients at home to monitor increasing trends in their bodyweight, which may be related to increased fluid retention  , BIB001 . With these potential advantages in mind, researchers have rigorously investigated this mode of BCG measurement. Inan et al. measured the mechanical frequency response of several commercially available scales at various loads to determine if the bandwidth was sufficient for BCG recording over a wide range of bodyweight. For bodyweights up to 160 kg, they found that the mechanical systems of most commercial scales have a bandwidth exceeding 15 Hz, which is sufficient for BCG measurement BIB003 . Note that for preserving the accuracy of time interval detection from the BCG, such as the R-J interval between the ECG and BCG, analog and digital low-pass filtering operations should not use a cutoff frequency lower than 25 Hz BIB005 . BCG measurement on a scale has also been successfully demonstrated by Gonzalez-Landaeta et al. BIB002 and Shin et al. BIB004 , and in all studies the shape and amplitude of the signal is very similar to the traditional BCG recordings taken by Starr et al. nearly a century earlier  .