Development of a Bed-Based Unconstrained Cardiac Auscultation Method

In this letter, we propose a bed-based unconstrained cardiac auscultation method to obtain heart sounds while a person is lying on a bed. In the proposed method, a sensing device with a resonance frequency in the frequency range of heart sounds is designed to improve the decreased gain of heart sounds through propagation in the bed mattress. In addition, the Wiener filter is applied to reduce the noise component contained in the measurement signals obtained by the proposed device. We performed a validation experiment to evaluate whether the proposed method correctly measures heart sounds by comparing the reference heart sounds measured by a stethoscope and those by the proposed device under a combination of conditions with different bed mattress thicknesses, sleeping postures, and respiratory states. The accuracy is evaluated by the correlation coefficient of the spectrum of heart sounds between the proposed method and the stethoscope. The experimental results demonstrate that the proposed unconstrained cardiac auscultation method can measure heart sounds with a correlation coefficient of 0.75 ± 0.12 on average.