Ballistocardiography and Seismocardiography: A Review of Recent Advances <s> B. Clinical Findings From Patients With Cardiovascular Disease <s> The duration of the systolic time intervals in nondigitalized patients with heart failure was determined from simultaneous fast speed recordings of the electrocardiogram, phonocardiogram, and carotid arterial pulsation. These were compared with the systolic time intervals corrected for heart rate and sex in 211 normal subjects. The failing left ventricle is characterized by a prolongation in the systolic pre-ejection period and a diminution in the left ventricular ejection time while total electromechanical systole remains relatively unaltered. Both components of the pre-ejection period, the Q-1 interval and the isovolumic contraction time, were prolonged. These alterations in the phases of systole occur in the absence of a measurable change in ventricular depolarization time. The prolongation in the pre-ejection period is well correlated with the reduced stroke volume and cardiac output in heart failure and is independently augmented by high levels of arterial pressure. The abbreviation in left ventricul... <s> BIB001 </s> Ballistocardiography and Seismocardiography: A Review of Recent Advances <s> B. Clinical Findings From Patients With Cardiovascular Disease <s> The relationships between the systolic time intervals determined from simultaneous recordings of the electrocardiogram, the phonocardiogram, the carotid arterial pulse tracing, and direct measures of left ventricular performance as assessed angiographically by measurement of left ventricular stroke volume (SV), end-diastolic volume (EDV), and ejection fraction (EF) were studied in 68 patients with a wide variety of cardiac diseases. The systolic intervals, the pre-ejection period (PEP), the left ventricular ejection time (LVET), and the ratio PEP/LVET, each correlated significantly with angiographically determined EF and EDV. Closest correlation was observed between PEP/LVET and EF (r = -0.90). The systolic intervals correlated only slightly with the angiographically determined SV. These data lend additional evidence supporting the use of systolic time intervals as a non-invasive measure of left ventricular performance in patients with cardiac disease. <s> BIB002 </s> Ballistocardiography and Seismocardiography: A Review of Recent Advances <s> B. Clinical Findings From Patients With Cardiovascular Disease <s> Seismocardiography, a new noninvasive technique, detects low-frequency cardiac vibrations on the chest wall during ventricular contraction and during both early and late ventricular filling. To evaluate the ability of seismocardiography to detect ischemia caused by decreased coronary blood flow, 35 patients were studied during coronary angioplasty. Seismocardiograms and electrocardiograms were recorded twice at baseline, with the catheter across the lesion before first inflation (n = 15), every 30 seconds during the first inflation, 1 and 2 minutes after the first inflation and greater than or equal to 5 minutes after the final inflation. For comparison, sequential seismocardiograms were also obtained from 15 healthy volunteers. Electrocardiograms were blindly scored for ST change from baseline (0 = none, 1 = 0.5 mm ST depression, 2 = greater than or equal to 1.0 mm ST depression, 3 = ST elevation). Seismocardiograms were blindly scored for change from baseline (0 = none, 1 = mild, 2 = moderate, 3 = marked) for both the systolic and diastolic waves. The average maximal systolic seismocardiographic score was 2.5 +/- 0.8 for patients who had undergone angioplasty and 1.0 +/- 0.9 for volunteers (p less than 0.001). The average maximal diastolic seismocardiographic score was 2.3 +/- 0.8 for angioplasty patients and 0.7 +/- 0.9 for volunteers (p less than 0.001). The percentage of angioplasty patients with electrocardiographic, systolic and diastolic seismocardiographic scores greater than or equal to 2 was, respectively: 0, 11 and 14% at second baseline; 23, 67 and 53% with catheter across the lesion; 44, 75 and 59% after 30 seconds of inflation; 42, 71 and 61% after 60 seconds of inflation; 23, 74 and 61% after 1 minute of deflation; and 0, 71 and 47% 5 minutes after final inflation.(ABSTRACT TRUNCATED AT 250 WORDS) <s> BIB003 </s> Ballistocardiography and Seismocardiography: A Review of Recent Advances <s> B. Clinical Findings From Patients With Cardiovascular Disease <s> A multicenter study was performed to compare the diagnostic accuracy of a new technique, seismocardiography, with that of electrocardiography for physiologically and anatomically significant ischemic coronary artery disease (CAD) during exercise stress testing. Five participating centers enrolled 129 patients who had simultaneous seismocardiograms and 12-lead electrocardiograms at the time of their exercise treadmill stress tests. Two different definitions of CAD were used: anatomic and physiologically significant disease. The presence of anatomically significant CAD (> or = 50% diameter stenosis) was documented by coronary angiography. Physiologically significant CAD was defined as present in the same 129 patients when coronary arteriography (> or = 50% diameter stenosis) and thallium-201 scintigraphy (defect on initial postexercise images) were both abnormal. Seismocardiography had a significantly better sensitivity for detecting anatomic CAD than did electrocardiography (73 vs 48%; p < 0.001), without loss of specificity (78 vs 80%; p = NS). Exercise seismocardiography added significant incremental diagnostic information beyond that provided by exercise electrocardiography. Seismocardiography was more sensitive (without less specificity) in women and in patients who did not achieve maximal predicted heart rate. In patients with physiologically significant CAD, the seismocardiogram was also significantly more sensitive (78%) than was the electrocardiogram (55%) (p < 0.02), without loss of specificity (84 vs 74%). Seismocardiography significantly improved sensitivity for the detection of anatomic and physiologic CAD. It is easy to perform and may be a clinically useful adjunct in exercise stress testing. <s> BIB004 </s> Ballistocardiography and Seismocardiography: A Review of Recent Advances <s> B. Clinical Findings From Patients With Cardiovascular Disease <s> BACKGROUND ::: Cardiac function time intervals are known to change with aerobic fitness. Recently, the Tei index of cardiac function [defined as the sum of the isovolumetric contraction (ICI) and isovolumetric relaxation intervals (IRI) divided by the left ventricular ejection time (LVET)] has been proposed to be a very sensitive determinant of cardiac function in patients with cardiomyopathy, i.e. the index is greater in patients with cardiomyopathy than it is in normal subjects. The purpose of this study was to determine the relationship between the Tei index and aerobic endurance in healthy volunteers. ::: ::: ::: METHODS ::: The relatively new noninvasive method of seismocardiography was used to measure following resting left ventricular (LV) cardiac function time intervals in 51 subjects (18 males and 33 females); Tei index, R-R interval, LV ICI, LV IRI, LVET, LV systole and LV diastole. Designated on the basis of peak treadmill time (Bruce protocol), the following three groups were assigned: Group 1; treadmill time > or = 900 seconds; Group 2: treadmill time ranging from 721 to 899 seconds; and Group 3; treadmill time < 720 seconds. ::: ::: ::: RESULTS ::: The Tei index value was lower as exercise capacity increased (p < 0.05) primarily due to a reduction in LV IRI (p < 0.05). LVET tended to be longer with increased treadmill time (p < 0.05) but this effect appeared to be secondary to a greater R-R interval in more fit subjects. When adjusted for the R-R interval, a reduced Tei index and LV IRI were still observed in more fit subjects, despite a similar LVET between groups. ::: ::: ::: CONCLUSIONS ::: Peak treadmill time is inversely related to the Tei index. A reduction of LV IRI appears to be the primary factor in establishing these differences. These data support the important role of LV diastolic function in aerobic fitness. <s> BIB005 </s> Ballistocardiography and Seismocardiography: A Review of Recent Advances <s> B. Clinical Findings From Patients With Cardiovascular Disease <s> Seismocardiography (SCG) is a methodology derived from the field of seismology to measure non-invasively compression waves generated by myocardial motion. The use of SCG is proposed here as method to monitor cardiac function during stress testing and magnetic resonance imaging (MRI). It is shown that recording of the seismocardiogram in subjects undergoing an MRI study is not compromised by flow-induced electrical voltages that can severely distort the electrocardiogram. Electromagnetic compatibility of the seismocardiograph device with the MRI scanner hardware was tested. Experiments in an animal model proved that changes in the SCG waveform during different levels of LAD stenosis correlate with the changes seen in LV function with cine MRI. The changes in the SCG waveform characteristic for the onset of ischemia were observed almost immediately after the creation of a flow-limiting stenosis. This novel application of SCG to monitor changes in peak acceleration from cardiac blood flow and wall motion may represent a solution to the long-standing and important problem of monitoring patients for signs of myocardial ischemia during MRI. <s> BIB006 </s> Ballistocardiography and Seismocardiography: A Review of Recent Advances <s> B. Clinical Findings From Patients With Cardiovascular Disease <s> INTRODUCTION ::: Changes due to biventricular pacing have been documented by shortening of QRS duration and echocardiography. Compared to normal ventricular activation, the presence of left bundle branch block (LBBB) results in a significant change in cardiac cycle time intervals. Some of these have been used to quantify the underlying cardiac dyssynchrony, assess the effects of biventricular pacing, and guide programming of ventricular pacing devices. This study evaluates a simple noninvasive method using accelerometers attached to the skin to measure cardiac time intervals in biventricularly paced patients. ::: ::: ::: METHODS ::: Ten patients with biventricular pacemakers previously implanted for congestive heart failure were paced in the AAI mode, then in atrioventricular (AV) sequential mode from the right and left ventricles followed by biventricular pacing. Simultaneous recordings were obtained by 2D, Doppler echocardiography as well as by accelerometers. Similar recordings were obtained from 10 gender, aged matched, normal controls during sinus rhythm. ::: ::: ::: RESULTS ::: Compared to normals, heart failure patients paced in AAI mode had prolonged isovolumetric contraction time (IVCT), shorter ventricular ejection time (LVET), and prolonged isovolumetric relaxation (IVRT). With biventricular pacing the IVCT decreased, but the LVET and IVRT did not change significantly. There was excellent correlation between the echo and accelerometer-measured intervals. ::: ::: ::: CONCLUSIONS ::: Shortening of the IVCT measured by an accelerometer is a consistent time interval change due to biventricular pacing that probably reflects more rapid acceleration of left ventricular ejection. The accelerometer may be useful to assess immediate efficacy of biventricular pacing during device implantation and optimize programmable time intervals such as AV and interventricular (VV) delays. <s> BIB007 </s> Ballistocardiography and Seismocardiography: A Review of Recent Advances <s> B. Clinical Findings From Patients With Cardiovascular Disease <s> Congestive heart failure has long been one of the most serious medical conditions in the United States; in fact, in the United States alone, heart failure accounts for 6.5 million days of hospitalization each year. One important goal of heart-failure therapy is to inhibit the progression of congestive heart failure through pharmacologic and device-based therapies. Therefore, there have been efforts to develop device-based therapies aimed at improving cardiac reserve and optimizing pump function to meet metabolic requirements. The course of congestive heart failure is often worsened by other conditions, including new-onset arrhythmias, ischemia and infarction, valvulopathy, decompensation, end-organ damage, and therapeutic refractoriness, that have an impact on outcomes. The onset of such conditions is sometimes heralded by subtle pathophysiologic changes, and the timely identification of these changes may promote the use of preventive measures. Consequently, device-based methods could in the future have an important role in the timely identification of the subtle pathophysiologic changes associated with congestive heart failure. <s> BIB008 </s> Ballistocardiography and Seismocardiography: A Review of Recent Advances <s> B. Clinical Findings From Patients With Cardiovascular Disease <s> A biomedical system embedded on a wheelchair able to measure heart rate, respiratory rate, and the wheelchair motion state is presented. A wireless multi-channel acquisition module is connected to a BCG (ballistocardiography) unit and to an inertial 3-axial MEMS accelerometer based unit. The sensing units are embedded on the seat and backrest of the wheelchair and the acquired data is transmitted through Wi-Fi connection to a remote processing unit expressed by a laptop PC. Considering the different motion situations of the wheelchair when utilized by the user, an important part of the work was focused on BCG noise and artifacts removal as well as to heart rate and respiratory rate accurate estimation from BCG signal using wavelet based filtering and ICA (Independent Component Analysis) algorithms. Experimental results for different scenarios of wheelchair utilization are included in the paper. <s> BIB009 </s> Ballistocardiography and Seismocardiography: A Review of Recent Advances <s> B. Clinical Findings From Patients With Cardiovascular Disease <s> We introduce and compare three different modalities to study seismocardiogram (SCG) and its correlation with cardiac events. We used an accelerometer attached to the subject sternum to get a reference measure. Cardiac events were then approximately identified using echocardiography. As an alternative approximation, we used consecutive Cine-MRI images of the heart to capture cardiac movements and compared them with the experimental SCG. We also employed an anatomically accurate, finite element base electromechanical model with geometry built completely from DT-MRI to simulate a portion of the cardiac cycle as observed in the SCG signal. The preliminary results demonstrate the usability of these newly proposed methods to investigate the mechanism of SCG waves and also demonstrate the usability of echocardiograph in interpretation of these results in terms of correlating them to underlying cardiac cycle events. <s> BIB010 </s> Ballistocardiography and Seismocardiography: A Review of Recent Advances <s> B. Clinical Findings From Patients With Cardiovascular Disease <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> BIB011 </s> Ballistocardiography and Seismocardiography: A Review of Recent Advances <s> B. Clinical Findings From Patients With Cardiovascular Disease <s> Due to recent technological improvements, namely in the field of piezoelectric sensors, ballistocardiography – an almost forgotten physiological measurement – is now being object of a renewed scientific interest. ::: ::: Transcending the initial purposes of its development, ballistocardiography has revealed itself to be a useful informative signal about the cardiovascular system status, since it is a non-intrusive technique which is able to assess the body’s vibrations due to its cardiac, and respiratory physiological signatures. ::: ::: Apart from representing the outcome of the electrical stimulus to the myocardium – which may be obtained by electrocardiography – the ballistocardiograph has additional advantages, as it can be embedded in objects of common use, such as a bed or a chair. Moreover, it enables measurements without the presence of medical staff, factor which avoids the stress caused by medical examinations and reduces the patient’s involuntary psychophysiological responses. ::: ::: Given these attributes, and the crescent number of systems developed in recent years, it is therefore pertinent to revise all the information available on the ballistocardiogram’s physiological interpretation, its typical waveform information, its features and distortions, as well as the state of the art in device implementations. <s> BIB012 </s> Ballistocardiography and Seismocardiography: A Review of Recent Advances <s> B. Clinical Findings From Patients With Cardiovascular Disease <s> The field of ballistocardiography seems to be enjoying a recent resurgence, most notably through the development of novel technologies and signal processing methods for measurement and analysis. After the method almost vanished in the late 80's and 90's, it is reasonable to wonder what is different this time, and if the technique has now more chances of becoming what its pioneer always wanted — a widespread clinical tool. This paper is an effort to compare and contrast this novel wave of research (notably in the context of the authors' own work). It also suggests that the new approaches have several key differences with past embodiments that place them in a good position to address some specific issues such as cardiac resynchronization therapy device optimization or congestive heart failure monitoring. This optimism is largely fed by the recent technological advances enabling the measurement of the BCG unobtrusively, frequently, at home or in a hospital, and by a re-focus on monitoring and trending applications. <s> BIB013 </s> Ballistocardiography and Seismocardiography: A Review of Recent Advances <s> B. Clinical Findings From Patients With Cardiovascular Disease <s> We report on the preliminary deployment of a bathroom scale-based ballistocardiogram (BCG) system for the in-hospital monitoring of patients with heart failure. These early trials provided valuable insights into the challenges and opportunities for such monitoring. In particular, the need for robust algorithms and adapted BCG metric is suggested. The system was designed to be robust and user-friendly, with dual ballistocardiogram (BCG) and electrocardiogram (ECG) capabilities. The BCG was measured from a modified bathroom scale, while the ECG (used as timing reference) was measured using dry handlebar electrodes. The signal conditioning and digitization circuits were USB-powered, and data acquisition performed using a netbook. Four patients with a NYHA class III at admission were measured daily for the duration of their treatment at Stanford hospital. A measure of BCG quality, in essence a quantitative implementation of the BCG classes originally defined in the 1950s, is proposed as a practical parameter. <s> BIB014 </s> Ballistocardiography and Seismocardiography: A Review of Recent Advances <s> B. Clinical Findings From Patients With Cardiovascular Disease <s> This paper presents an overview of seismocardiography (SCG) as a noninvasive cardiology method. The paper represents a brief historical background to the SCG, an assessment of the technology at present, and an evaluation of the challenges we must address. These challenges include the development and clarification of definitions, standards, and annotations. <s> BIB015 </s> Ballistocardiography and Seismocardiography: A Review of Recent Advances <s> B. Clinical Findings From Patients With Cardiovascular Disease <s> We present a study on the feasibility of the automatic detection of atrial fibrillation (AF) from cardiac vibration signals (ballistocardiograms/BCGs) recorded by unobtrusive bed-mounted sensors. The proposed system is intended as a screening and monitoring tool in home-healthcare applications and not as a replacement for ECG-based methods used in clinical environments. Based on the BCG data recorded in a study with ten AF patients, we evaluate and rank seven popular machine learning algorithms (naive Bayes, linear and quadratic discriminant analysis, support vector machines, random forests as well as bagged and boosted trees) for their performance in separating 30-s long BCG epochs into one of three classes: sinus rhythm, AF, and artifact. For each algorithm, feature subsets of a set of statistical time-frequency-domain and time-domain features were selected based on the mutual information between features and class labels as well as the first- and second-order interactions among features. The classifiers were evaluated on a set of 856 epochs by means of tenfold cross validation. The best algorithm (random forests) achieved a Matthews correlation coefficient, mean sensitivity, and mean specificity of 0.921, 0.938, and 0.982, respectively. <s> BIB016 </s> Ballistocardiography and Seismocardiography: A Review of Recent Advances <s> B. Clinical Findings From Patients With Cardiovascular Disease <s> Cardiac resynchronization therapy (CRT) is the therapy of choice for selected patients suffering from drug-refractory congestive heart failure and presenting an interventricular desynchronization. CRT is delivered by an implantable biventricular pacemaker, which stimulates the right atrium and both ventricles at specific timings. The optimization and personalization of this therapy requires to quantify both the electrical and the mechanical cardiac functions during the intraoperative and postoperative phases. The objective of this paper is to evaluate the feasibility of the calculation of features extracted from endocardial acceleration (EA) signals and the potential utility of these features for the intraoperative optimization of CRT. Endocardial intraoperative data from one patient are analyzed for 33 different pacing configurations, including changes in the atrio-ventricular and inter-ventricular delays and different ventricular stimulation sites. The main EA features are extracted for each pacing configuration and analyzed so as to estimate the intra-configuration and inter-configuration variability. Results show the feasibility of the proposed approach and suggest the potential utility of EA for intraoperative monitoring of the cardiac function and defining optimal, adaptive pacing configurations. <s> BIB017
Modern ballistocardiography and seismocardiography systems may be capable of monitoring slow, longitudinal changes in cardiac function associated with a number of cardiovascular diseases. Timely noninvasive detection of subtle changes in cardiac pathophysiology may one day enable daily drug dosage adjustments, thus reducing costly and morbid rehospitalizations BIB008 . At this moment, the feasibility of this approach is investigated by the ongoing LAPTOP-HF study which, however, uses an implantable right atrial pressure sensor coupled to a mobile device that allows daily automatic dosage adjustment [95] . Fortunately, the basis for the SCG's clinical utility was begun in 1990 with the initial use of high sensitivity, LF accelerometers to measure precordial vibrations  . Significant features of the SCG waveform were identified and associated with key events in the cardiac cycle  . This allowed the accurate measurement of these features (e.g., ACs and MOs) using one sensor, greatly simplifying the calculation of CTIs. A large body of work exists on the utility and efficacy of CTIs BIB001 , BIB002 . This knowledge combined with the ability to make accurate, repeatable quantitative measurements using the SCG resulted in the ability to conduct clinically relavent crosssectional studies. Subsequently, clinical studies were undertaken to determine if the SCG could be used to identify changes in the SCG waveform resulting from myocardial ischemia BIB003 . The SCG's clinical utility in enhancing the diagnostic outcome of a graded exercise stress test was first shown in  . A large multicenter study demonstrated that when the combined results of the ECG and SCG were used, the predictive accuracy of detecting physiologically significant coronary artery disease was increased significantly over the results of the ECG alone BIB004 . The introduction in the early 1990s of lightweight (<25g) accelerometers, whose working range extended below 1 Hz, made possible other clinical settings for the SCG. The SCG as a magnetic-field-compatible alternative to the electrocardiogram for cardiac stress monitoring BIB006 was made possible using a newly introduced light weight piezoelectric accelerometer (336C, PCB Piezotronics, Depew, NY, USA). The SCG was used to measure CTI's during atrial, ventricular, and biventricular pacing, as compared to normals BIB007 . One of the studies objectives was to determine the utility of the SCG in cardiac resynchronization therapy (CRT). This study was the first to use 3 SCG traces for analysis, i.e., one accelerometer was placed on the xyphoid process, a second over the apex at the fourth intercostal, and a third on the right carotid pulse. In 1994, the SCG was used to make accurate longitudinal measurements in a study of the effects of elgodiphine on cardiac hemodynamics  . In a sports medicine application, exercise capacity was evaluated using the SCG BIB005 . A more extensive review of the SCG is available in BIB015 . As a note of interest, the combined patient population of the myocardial ischemia studies BIB004 ,  is close to 2000 and consists of both healthy and disease subjects. All the raw data were recorded with the same instrumentation (SCG 2000, SeisMed Instruments, Minneapolis, MN, USA) associated with these datasets are complete patient demographics. A project is underway to make the raw data available on the PhysioNet website for study by interested researchers BIB015 . More recent findings with BCG and SCG further support that the signals have great potential in allowing proactive cardiac disease management without a costly implantable device. However, despite stated clinical and/or physiologic motivations, the overwhelming majority of modern BCG/SCG findings continue to be from healthy subjects BIB012 BIB009 BIB010 . Notable exceptions include a bed-mounted BCG system for automated detection of atrial fibrillation BIB016 , the observation of reduced signal amplitude in the setting of premature atrial or ventricular contractions BIB011 , and the reduction of signal consistency in heart failure patients concordant with worsening clinical outcome BIB014 . One particular subset of patients is particularly well suited for study using cardiomechanical signals, those undergoing CRT. CRT patients have abnormal cardiac conduction causing in a significant delay between the pumping action of the various chambers of the heart. CRT involves precisely adjusting the timing of a multichamber pacemaker to reduce or remove these delays. Such timing is difficult to ascertain using available technologies, spawning the field of "CRT optimization." Researchers recently demonstrated the benefits of intracardiac acceleration monitoring in performing CRT optimization BIB017 , a finding preliminarily corroborated by BCG findings as well BIB013 .