Ballistocardiography and Seismocardiography: A Review of Recent Advances <s> A. Wearable BCG or SCG Systems <s> Seismocardiogram (SCG) is the recording of body vibrations induced by the heart beat. SCG contains information on cardiac mechanics, in particular heart sounds and cardiac output. In this paper we present a new wearable device for SCG recordings during long term monitorings, and the results of a validation test in 4 subjects. The system is based on the integration of the MagIC smart shirt (i.e., a textile-based wearable system for the assessment of ECG and respiratory movements), and an external triaxial MEMS accelerometer positioned on the left clavicle. SCG was estimated as the average of accelerations occurred in each heart beat. The SCG components due to the valve closure and to recoil forces following the heart contraction (ballistocardiogram) were extracted by high-pass (>18 Hz) and band-pass (0.6-20 Hz) filters respectively. Then the difference between the I and J waves of the ballistocardiogram ( lI-Jl index, possibly related to the cardiac output) was identified by an ad-hoc procedure and compared with the model flow indirect estimation of cardiac output. Validation on 4 volunteers showed that: 1) our wearable system provides statistically consistent estimates of both heart- sound related vibrations and recoil movements; 2) reliable estimates of the II-Jl index can be obtained by considering about 1 minute of SCG recording in stationary conditions; and 3) changes of the II-Jl index during exercise correlate well with changes of cardiac output estimated by the model flow. <s> BIB001 </s> Ballistocardiography and Seismocardiography: A Review of Recent Advances <s> A. Wearable BCG or SCG Systems <s> Abstract Investigations of blood pressure, heart rate (HR), and heart rate variability (HRV) during long term space flights on board the “ISS” have shown characteristic changes of autonomic cardiovascular control. Therefore, alterations of the autonomic nervous system occurring during spaceflight may be responsible for in- and post-flight disturbances. The device “Pneumocard” was developed to further investigate autonomic cardiovascular and respiratory function aboard the ISS. The hard-software diagnostic complex “Pneumocard” was used during in-flight experiment aboard ISS for autonomic function testing. ECG, photoplethysmography, respiration, transthoracic bioimpedance and seismocardiography were assessed in one male cosmonaut (flight lengths six month). Recordings were made prior to the flight, late during flight, and post-flight during spontaneous respiration and controlled respiration at different rates. HR remained stable during flight. The values were comparable to supine measurements on earth. Respiratory frequency and blood pressure decreased during flight. Post flight HR and BP values increased compared to in-flight data exceeding pre-flight values. Cardiac time intervals did not change dramatically during flight. Pulse wave transit time decreased during flight. The maximum of the first time derivative of the impedance cardiogram, which is highly correlated with stroke volume was not reduced in-flight. Our results demonstrate that autonomic function testing aboard the ISS using “Pneumocard” is feasible and generates data of good quality. Despite the decrease in BP, pulse wave transit time was found reduced in space as shown earlier. However, cardiac output did not decrease profoundly in the investigated cosmonaut. Autonomic testing during space flight detects individual changes in cardiovascular control and may add important information to standard medical control. The recent plans to support a flight to Mars, makes these kinds of observations all the more relevant and compelling. <s> BIB002 </s> Ballistocardiography and Seismocardiography: A Review of Recent Advances <s> A. Wearable BCG or SCG Systems <s> Practical usability of the majority of current wearable body sensor systems for multiple parameter physiological signal acquisition is limited by the multiple physical connections between sensors and the data-acquisition modules. In order to improve the user comfort and enable the use of these types of systems on active mobile subjects, we propose a wireless body sensor system that incorporates multiple sensors on a single node. This multisensor node includes signal acquisition, processing, and wireless data transmission fitted on multiple layers of a thin flexible substrate with a very small footprint. Considerations for design include size, form factor, reliable body attachment, good signal coupling, low power consumption, and user convenience. The prototype device measures 55 15 mm and is 3 mm thick. The unit is attached to the patient's chest, and is capable of performing simultaneous measurements of parameters, such as body motion, activity intensity, tilt, respiration, cardiac vibration, cardiac potential (ECG), heart rate, and body surface temperature. In this paper, we discuss the architecture of this system, including the multisensor hardware, the firmware, a mobile-phone receiver unit, and assembly of the first proof-of-concept prototype. Preliminary performance results on key elements of the system, such as power consumption, wireless range, algorithm efficiency, ECG signal quality for heart-rate calculations, as well as synchronous ECG and body activity signals are also presented. <s> BIB003 </s> Ballistocardiography and Seismocardiography: A Review of Recent Advances <s> A. Wearable BCG or SCG Systems <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> BIB004 </s> Ballistocardiography and Seismocardiography: A Review of Recent Advances <s> A. Wearable BCG or SCG Systems <s> Continuous and wearable heart monitoring is essential for early detection and diagnosis of cardiovascular diseases. We demonstrate a continuous, wearable, and wireless heart monitor that is worn at the ear. The device has the form factor of a hearing aid and is wirelessly connected to a PC for data recording and analysis. With the ear as an anchoring point, the heart monitor measures the ballistocardiographic (BCG) motion of the head using a MEMS tri-axial accelerometer, which is an electrode-less method to measure heart rate. Additionally, electrocardiogram (ECG) is measured locally near the ear using a single-lead configuration. The peak timing delay between the head ECG and the head BCG, or RJ interval, can be extracted in the presence of noise using cross-correlation. The RJ interval is shown to correlate to the heart's pre-ejection period during both Valsalva and whole-body tilt maneuvers. <s> BIB005 </s> Ballistocardiography and Seismocardiography: A Review of Recent Advances <s> A. Wearable BCG or SCG Systems <s> A continuous, wearable and wireless vital signs monitor at the ear is demonstrated. The device has the form factor of a hearing aid and is wirelessly connected to a PC for data recording and analysis. The device monitors the electrocardiogram (ECG) in a single lead configuration, the ballistocardiogram (BCG) with a MEMS triaxial accelerometer, and the photoplethysmograms (PPG) with 660 nm and 940 nm LED sources and a static photocurrent subtraction analog front end. Clinical tests are conducted, including Valsalva and head-up tilt maneuvers. Peak timing intervals between the ECG, BCG and PPG are extracted and are shown to relate to pre-ejection period and mean arterial blood pressure (MAP). Pulse Transit Time (PTT) extracted from cross-correlation between the PPG and BCG shows improved results compared to the pulse arrival time (PAT) method for tracking changes in MAP. <s> BIB006 </s> Ballistocardiography and Seismocardiography: A Review of Recent Advances <s> A. Wearable BCG or SCG Systems <s> Abstract Seismocardiogram (SCG) is the measure of the micro-vibrations produced by the heart contraction and blood ejection into the vascular tree. Over time, a large body of evidence has been collected on the ability of SCG to reflect cardiac mechanical events such as opening and closure of mitral and aortic valves, atrial filling and point of maximal aortic blood ejection. We recently developed a smart garment, named MagIC-SCG, that allows the monitoring of SCG, electrocardiogram (ECG) and respiration out of the laboratory setting in ambulant subjects. The present pilot study illustrates the results of two different experiments performed to obtain a first evaluation on whether a dynamical assessment of indexes of cardiac mechanics can be obtained from SCG recordings obtained by MagIC-SCG. In the first experiment, we evaluated the consistency of the estimates of two indexes of cardiac contractility, the pre-ejection period, PEP, and the left ventricular ejection time, LVET. This was done in the lab, by reproducing an experimental protocol well known in literature, so that our measures derived from SCG could have been compared with PEP and LVET reference values obtained by traditional techniques. Six healthy subjects worn MagIC-SCG while assuming two different postures (supine and standing); PEP was estimated as the time interval between the Q wave in ECG and the SCG wave corresponding to the opening of aortic valve; LVET was the time interval between the SCG waves corresponding to the opening and closure of the aortic valve. The shift from supine to standing posture produced a significant increase in PEP and PEP/LVET ratio, a reduction in LVET and a concomitant rise in the LF/HF ratio in the RR interval (RRI) power spectrum. These results are in line with data available in literature thus providing a first support to the validity of our estimates. In the second experiment, we evaluated in one subject the feasibility of the beat-by-beat assessment of LVET during spontaneous behavior. The subject was continuously monitored by the smart garment from 8 am to 8 pm during a workday. From the whole recording, three data segments were selected: while the subject was traveling to work (M1), during work in the office (O) and while traveling back home (M2). LVET was estimated on a beat-by-beat basis from SCG and the RRI influence was removed by regression analysis. The LVET series displayed marked beat-by-beat fluctuations at the respiratory frequency. The amplitude of these fluctuations changed in the three periods and was lower when the LF/HF RRI power ratio was higher, at O, thus suggesting a possible influence of the autonomic nervous system on LVET short-term variability. To the best of our knowledge this case report provides for the first time a representation of the beat-by-beat dynamics of a systolic time interval during daily activity. The statistical characterization of these findings remains to be explored on a larger population. <s> BIB007 </s> Ballistocardiography and Seismocardiography: A Review of Recent Advances <s> A. Wearable BCG or SCG Systems <s> 3D-Ballistocardiograms ECG and Impedancecardiograms (ICG) were recorded on 5 healthy volunteers participating to the European Space Agency (ESA) 57(th) parabolic flights campaigns. Comparisons are made between the baseline recordings performed on the ground and the recordings made during the microgravity phases of a parabolic flight. The spatial curves of the displacement, velocity and acceleration vectors, instead of their individual components are used to compute the magnitude of the force vector, kinetic energy and work during the cardiac cycle. Our hypothesis is that the 3D-BCG provides parameters correlated with the timings of ejection (PEP, LVET). Although our subject population is limited (N=5), this is the first study of BCG to be performed with N>1. Our results suggest that microgravity decrease the complexity of the 3D displacement curve and that peaks in curvature are consistently present in microgravity and on the ground. However they do not seem to be perfectly related to the classical cardiac ejection timings from ICG. <s> BIB008 </s> Ballistocardiography and Seismocardiography: A Review of Recent Advances <s> A. Wearable BCG or SCG Systems <s> The transthoracic impedance cardiogram (ICG) and the acceleration ballistocardiogram (BCG) measured close to the center of mass of the human body are generated by changes of blood distribution. The transthoracic ICG is an integrated signal covering the whole thorax and spatial resolution is poor. Comparison between both signals can be used to elucidate the source of the ICG signal. We recorded the ECG, ICG, and BCG simultaneously in healthy subjects under resting and microgravity conditions during parabolic flights. The time interval between the R-peak of the ECG and the maximum of the ICG (R-dZ/dtmax) and the time interval between the R-peak of the ECG and the I-peak in the BCG (R-I) differed significantly (p<;0.0001). The I-peak in the BCG always occurred earlier during systole than dZ/dtmax. The delay of dZ/dtmax ranged between 23 and 28 ms at rest and was lowest under microgravity conditions (12±4 ms, p<;0.02). Our results suggest that both signals have different sources. Combination of modern imaging techniques with classical non invasive approaches to detect changes of blood distribution may provide new insights into the complex interaction between blood flow and mechanocardiographic signals like the BCG. <s> BIB009 </s> Ballistocardiography and Seismocardiography: A Review of Recent Advances <s> A. Wearable BCG or SCG Systems <s> This paper presents a comparison of the cardiovascular changes observed in microgravity as compared to ground based measurements. The ballistocardiogram (BCG), the electrocardiogram (ECG) and the transthoracic impedance cardiogram (ICG) were recorded on five healthy subjects during the 57th-European Space Agency (ESA) parabolic flight campaign. BCG is analyzed though its most characteristic wave, the IJ wave complex that can be identified along the longitudinal component of BCG and which has been demonstrated to be linked to cardiac ejection. The timings between the contraction of the heart and the ejection of blood in the aorta are analyzed via the time delay between the R-wave of the ECG and the I and J-waves of BCG (RI and RJ intervals respectively). Our results show that the IJ complex presents a larger amplitude in weightlessness and suggest that stroke volume (SV) increases in microgravity. We assume that ballistocardiography is an efficient method to assess the ventricular performance. <s> BIB010 </s> Ballistocardiography and Seismocardiography: A Review of Recent Advances <s> A. Wearable BCG or SCG Systems <s> We extract heart rate and beat lengths from videos by measuring subtle head motion caused by the Newtonian reaction to the influx of blood at each beat. Our method tracks features on the head and performs principal component analysis (PCA) to decompose their trajectories into a set of component motions. It then chooses the component that best corresponds to heartbeats based on its temporal frequency spectrum. Finally, we analyze the motion projected to this component and identify peaks of the trajectories, which correspond to heartbeats. When evaluated on 18 subjects, our approach reported heart rates nearly identical to an electrocardiogram device. Additionally we were able to capture clinically relevant information about heart rate variability. <s> BIB011 </s> Ballistocardiography and Seismocardiography: A Review of Recent Advances <s> A. Wearable BCG or SCG Systems <s> The ElectroMechanical Film (EMFi), a thin and flexible piezoelectric material, has been widely used as a mechanical sensor or actuator. Especially in Biomedical Engineering field, many researchers have used EMFi for measuring ballistocardiogram (BCG) which is a mechanical signal caused by blood ejection from heart. However, previous methods required special equipments installed on a chair or a bed to measure BCG. In this preliminary study, we designed a flexible patch type sensor that can measure electrical and mechanical signal simultaneously on a single unit. The Ballistocardiogram-Electrocardiogram patch (BEpatch), integrated with flexible circuit and attached to chest, can successfully measure fine electrocardiogram (ECG) and BCG signals simultaneously. The result shows that BEpatch can be used for continuous monitoring of bio-signals in a simple and comfortable manner, thereby, advantageous as a wearable health care device. <s> BIB012
The primary advantage of wearable BCG or SCG measurement systems is the possibility of obtaining data continuously throughout normal daily living. Additionally, recordings with wearable systems can potentially be acquired in any environment; thus, providing an opportunity to assess a person's cardiovascular performance under various environmental settings or stressors. The sensor type used most often for wearable BCG or SCG measurements is an accelerometer, typically with three-axis measurement capability, that is mechanically coupled to the body with either adhesives, plastic mounting, or textiles. In 2007, Castiglioni et al. tested the SCG assessment by an external three-axis MEMS accelerometer placed on the left clavicle, connected to a smart garment with textile ECG electrodes, thus obtaining simultaneous tri-axial SCG and single-lead ECG recordings BIB001 . The concept was subsequently refined, and in 2010, Di Rienzo et al. proposed an integrated vest equipped with sensors, the MagIC-SCG device, in which the accelerometer was inside the system electronics and placed in contact with the subject's sternum BIB004 . Through this system, SCG was recorded over 24 h in ambulant subjects, while performing a variety of activities of normal daily living and beat-to-beat estimates of cardiac time intervals (CTIs) could be estimated BIB007 . Chuo et al. developed miniaturized hardware (55 × 15 × 3 mm) on a flexible substrate with adhesive backing for wireless tri-axial SCG recording from the sternum (also with a MEMS accelerometer) together with single-lead ECG and coarse single-point skin temperature via a thermistor BIB003 . Baevsky et al. developed a portable system, "Pneumocard," for the assessment of the cardiac function of cosmonauts on board the International Space Station BIB002 . The system comprised a single-axis MEMS accelerometer placed at the apex of the heart for the recording of the SCG signal. Later, a three-axis MEMS accelerometer was added to the system for the recording of the BCG signal. The accelerometer was placed on the back of the subject, either at the center of mass or between the scapulae and its performance during the microgravity phases of parabolic flights was tested by Migeotte et al. BIB008 BIB009 BIB010 . He et al. placed a tri-axial MEMS accelerometer for BCG measurement in a plastic mount over the ear, with auxiliary sensors included for ECG and / or photoplethysmogram (PPG) measurement, respectively, BIB005 , BIB006 . Hyun et al. used an electromechanical film (EMFi) patch to measure the vibrations of the chest wall in the dorso-ventral direction (transverse); however, it should be noted that the exact position on the chest for the measurement was not provided, and on the basis of morphology, while the signal was called the BCG, it was likely rather an SCG BIB012 . Another notable approachthat is not exactly a wearable device, but provides some similar advantages-was demonstrated by Balakrishnan et al. with the head-to-foot (longitudinal) direction ballistocardiographic displacements of the head being captured and processed from video recordings BIB011 .