Bedding waveguide for smartphone-based ballistocardiography

Ballistocardiography (BCG), a contactless heart rate monitoring method, has the potential to measure vital signs and reduce neonates’ monitoring pain and discomfort. It uses an accelerometer on the mattress side. However, the bedding and bed frame nature may alter the propagation of the ejection force to the sensor, especially in case of viscous foam or damping medical beds. As neonates have a weaker ejection force than adults, heartbeats are sometimes undetectable with usual BCG systems.The contribution of the bedding nature to the BCG amplitude is investigated and a waveguide bedding is designed to amplify the BCG signal: a healthy adult volunteer is asked to rest in supine position on a bed. A contactless accelerometer records the BCG for one minute on the bed surface, twenty centimeters away from the thorax. Amplitude of heartbeats are compared for different waveguide beddings, with or without a mattress cover. Another experimentation applies this principle with a smartphone that includes an accelerometer without any hardware amplification, in comparison with a usual BCG system. The selected waveguides beddings significantly amplify up to 50 % the smallest heartbeats in the BCG signal. The smartphone BCG was also amplified with the waveguide bedding and heartbeats could be detected.The choice of bedding and bed frame must be considered for BCG measurement systems. Waveguides beddings amplify the ejection force generated during systole and offer opportunities to develop a smartphone-based contactless monitoring method for the mechanical cardiac activity of neonates.