Measurement of heartbeat intervals in a sitting position using multiple piezoelectric sensors with body movement reduction

In this study, we proposed a measurement system that extracts heartbeat interval data from multiple piezoelectric sensors placed on a chair that eliminates noise generated by body movement. We asked five healthy males (21-24 years old) to sit in an arbitrary position on a chair that had eight piezoelectric sensors attached, and heartbeat signals were measured. The experiment consisted of four measurements (5 min measurements after adequate rest), while performing specific body movements at a specific time, with deliberately mixed noise of body movements. To remove body movement noise, bandpass filter processing (4 Hz-20 Hz) was applied to the signal obtained from the piezoelectric sensors, and the heartbeat component was extracted using independent component analysis (number of separations was eight) on the processed waveform. For verification, the error rate was obtained before and after the removal of body movement noise, respectively. The error rate after removal of body motion was 2.91 ± 0.75%. In our previous study with two piezoelectric sensors without body movement, the error rate was 2.47 ± 2.66%. Therefore, our proposed measurement system may improve the accuracy of heartbeat interval detection, which can be observed continuously by removing the body motion.