Ballistocardiogram (BCG) Measurement by a Differential Pressure Sensor

A ballistocardiogram (BCG) is a recording of the mechanical movement of the body caused by cardiac ejection of blood. We propose a method to obtain the BCG of a body by utilizing the pressure inside a sensor tube placed between a cushion and a bed frame. A theoretical model of the propagation of movement through the cushion that generates pressure is presented to investigate the cushion viscoelasticity effect. The stiffness constants and damping coefficient of an elastic cushion and a memory foam cushion were investigated. We also investigated the influence of the sensor tube diameter on sensitivity and the propagation of mechanical movement through these different cushions. Finally, the BCG of a subject was measured for various cushion conditions and the S/N ratios of all cases were evaluated to find the optimal sensor tube and placement conditions. The sensitivity is proportional to the sensor tube diameter and the S/N ratio is almost inversely proportional to the cushion thickness. However, for all cases, the S/N ratio ranges from 26.4 dB to 44.3 dB. The best sensor tube placement was under the neck. The experimental results revealed the same trends as the analysis of the model.