Non-Contact Capacitive Ballistocardiogram Measurements Using In-Bed Fabric-Sheet Electrode for Blood Pressure Estimation

We recently reported the possibility of the simultaneous measurement of capacitive electrocardiogram (cEGC) and capacitive ballistocardiogram (cBCG) using non-contact capacitive coupling systems in bed. However, the relations of the two measurements with blood pressure (BP) have not been elucidated and cBCG measurements were unstable. Therefore, in this study, electrodes and systems for cEGC measurements were excluded, concerning the potential influence of interference. Electrode size was changed to stabilize cBCG measurements. The Valsalva test (VT) was performed on five subjects, and the correlations with BP were determined. A synchronous averaging process was performed to confirm waveform similarity to the ballistocardiogram (BCG) and its reproducibility. We examined the relation between pulse beat arrival time (PBAT) and systolic blood pressure (SBP) and PBAT and pulse arrival time (PAT) after 10 s of VT termination and observed a high negative correlation with SBP and a high positive correlation with PAT in three subjects. cBCG contains components that are strongly related to BP. In future, we will conduct simultaneous measurements with cECG and improve the electrode to simultaneously measure cBCG at two points at constant intervals to avoid shifting of PBAT time axis.