Question

Please write a detailed review/discussion over seismocardiography. Include things such as the pros/cons and compare it to other methods, etc.

Answer 1

   Seismocardiography (SCG) is the recording of body vibrations induced by the heart beat.This term was popularized by the works of Salerno and Zanetti at the beginning of the 90’s.SCG contains information on cardiac mechanics,in particular heart sounds and cardiac output.According to the measured quantity (displacement, velocity or acceleration) and sensors position, this method has been called apex-cardiography,kineto-cardiography,cardio-kymocardiography or ballistocardiography,this latter being probably the more widely used term.

   Vibrations induced by the cardiac activity are mainly correlated to valve closure (heart sounds) and cardiac systole. In particular, SCG movements at relatively lower frequencies reflect the recoil forces that results from the contraction of the heart muscle ejecting blood into the vessels. These forces are responsible for body accelerations in the order of 5 mg.

ascg SCG Sensor B Head-to-Foot 7 cm O Lateral Dorso-Ventral

Figure 1:Seismocardiogram (SCG) and ECG sensing patch. A, The SCG signal represents the vibrations of the chest wall in response to the movement of the heart and blood with each heartbeat. SCG is measured using a miniature, 3-axis accelerometer, typically positioned on the midsternum. B, The SCG signal consists of vibrations in 3 axes: head-to-foot, dorso-ventral, and lateral. C, A custom, small, wearable patch for measuring SCG and ECG signals was designed. The patch is placed on the chest using 3 gel adhesive electrodes and stores data locally on a micro secure digital card. The low power design allows for >50 h of continuous recording and use without recharging the battery.

The ballistocardiogram (BCG) is a measurement of the recoil forces of the body in reaction to cardiac ejection of blood into the vasculature,while the seismocardiogram(SCG)represents the local vibrations of the chest wall in response to the heartbeat.The BCG phenomenon was ?rst observed in 1877 by Gordon, with the ?nding that, as a subject would stand on a weighing scale, the needle would vibrate synchronously to the subject’s heartbeat.Nearly 60 years later,Starr and colleagues created an instrument in the form of a table with a mobile top surface to measure the BCG in a repeatable scienti?c manner. The SCG was ?rst observed by Bozhenko in 1961, and was ?rst applied in clinical studies 30 years later in 1991 by Salerno and Zanetti. Throughout the 1900s, both BCG and SCG signals were heavily investigated and several publications appeared in major scienti?c and clinical journals. However,because of the advent of echocardiography and magnetic resonance imaging, and overly-cumbersome hardware, BCG and SCG were largely abandoned by the medical community.

ECG Diastole Ao Systole AC RE AS RF MC SCG MC IM MO

Figure 2: Seismocardiogram. MC = Mitral valve closure; IM = isovolumic movement; AO = aortic valve opening; IC = isotonic contraction; RE = rapid ventricular ejection; AC = aortic valve closure; MO = mitral valve opening; RF = rapid ventricular filling; AS = atrial systole; EMD = electromechanical delay

   SCG is the measure of the thoracic vibrations produced by the heart’s contraction and the ejection of blood from the ventricles into the vascular tree.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 milligram; 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.

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.