Low frequency vibration signals are those vibrations that have their main component in infrasonic range (less than 20 Hz) or slightly higher and up to 30 Hz. These signals are displacement, velocity, or acceleration of the body in response to the heart beating and recorded from different parts of the body or the platforms on which the body rests. These signals can provide information regarding the mechanical functioning of the heart as a pump, by quantifying the pulses appearing on the body with every heartbeat. Over the past century, extensive research has been conducted on interpretation of these signals in terms of their relationship to cardiovascular dynamics and their possible use in diagnostic cardiology. Today, new microelectronics and signal processing technologies have provided unprecedented opportunities to reintroduce some of these relatively old techniques as useful cardiac diagnostic and monitoring tools.
There are two distinct categories of infrasonic cardiac signals. In the first category the signal is created by changes of the centre of gravity of the whole or upper part of the body as the result of blood circulation. These centre of mass recordings include signals such as: ballistocardiogram (BCG), dynamocardiogram, quantitative seismocardiography (Q-SCG), quantitative ballistocardiogram (Q-BCG) and EMFit. Normally, these signals are recorded by setting up a recording platform on which the subject can lie, sit or stand, and both subject and the platform are free to move with every heartbeat.
The second category contains surface measurements made from regions localized near the heart where pulsations over the heart (precordium) are recorded. Seismocardiogram (SCG), apexcardiogram (ACG), sternal acceleration ballistocardiography (SAB), kinetocardiogram (KCG), mechanocardiogram (MCG), and vibrocardiogram belong to this category.
Ballistocardiogram from the first category and Seismocardiogram from the second category have had a lot of attention during the past decade and are of special interest to BERC.