Simultaneous Measurements of Capacitive Electrocardiogram and Ballistocardiogram 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, we improved the electrode and circuit, and succeeded in stable simultaneous measurement of cECG and cBCG. Synchronous averaging was performed to confirm the similarity of the waveform to the reproducibility of cBCG. Valsalva test (VT) was performed on seven subjects, and four verification intervals were set after VT. Then, the estimated blood pressure value was calculated using the instantaneous heart rate as the time difference parameter. We examined the relationship between estimated systolic blood pressure (eSBP) and systolic blood pressure (SBP) and observed a high positive correlation. cBCG contains components that are strongly related to BP. In the future, the electrode will be improved to measure cBCG at two points simultaneously at regular intervals to avoid shifting the Pulse Beat Arrival Time (PBAT) time axis. Further, in order to enhance the accuracy of blood pressure estimation, a change in the respiratory phase is incorporated into the estimation of the blood pressure value.

A Novel Analog Front End with Voltage-Dependent Input Impedance and Bandpass Amplification for Capacitive Biopotential Measurements.

This paper proposes a novel analogue front end (AFE) that has three features: voltage-dependent input impedance, bandpass amplification, and stray capacitance reduction. With a view to applying the AFE to capacitive biopotential measurements (CBMs), the three features were investigated separately in a schematic and mathematical manner. Capacitive electrocardiogram (cECG) or capacitive electromyogram (cEMG) measurements using the AFE were performed in low-humidity conditions (below 35% relative humidity) for a total of seven human subjects. Performance evaluation of the AFE revealed the following: (1) the proposed AFE in cECG measurement with 1.70-mm thick clothing reduced the baseline recovery time and root mean square voltage of respiratory interference in subjects with healthy-weight body mass index (BMI), and increased R-wave amplitude for overweight-BMI subjects; and (2) the proposed AFE in cEMG measurement of biceps brachii muscle yielded stable electromyographic waveforms without the marked DC component for all subjects and a significant (p < 0.01) increase in the signal-to-noise ratio. These results indicate that the proposed AFE can provide a feasible balance between sensitivity and stability in CBMs, and it could be a versatile replacement for the conventional voltage follower used in CBMs.

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.