Heart Rate Detection From Plantar Bioimpedance Measurements

Abstract

In this paper, a novel technique for heart rate measurement on a standing subject is proposed that relies on electrical impedance variations detected by a plantar interface with booth feet, such as those in some bathroom weighting scales for body composition analysis. Heart-related impedance variations in the legs come from arterial blood circulation and are below 500 mOmega. To detect them, we have implemented a system with a gain in excess of 600, and whose fully differential AC input amplifier has a gain of 4.5 and a common-mode rejection ratio (CMRR) higher than 90 dB at 10 kHz. Differential coherent demodulation based on synchronous sampling yields a signal-to-noise ratio (SNR) of about 54 dB . The system sensitivity is 610 mV/Omega. The technique has been demonstrated on 18 volunteers, whose bioimpedance signal and ECG were simultaneously recorded. A Bland-Altman plot shows a mean bias of -0.2 ms between the RR time intervals obtained from these two signals, which is negligible. The technique is simple and user friendly and does not require any additional sensors or electrodes attached to the body, hence no conductive gel or skin preparation.

A 3.9 mW 25-Electrode Reconfigured Sensor for Wearable Cardiac Monitoring System

“…The proposed 4-layer compact plaster sensor detects ECG and TIV signals concurrently with 16 different electrode configurations. The maximum impedance detection sensitivity is 3.17 V which is more sensitive than [12] by 5 times, and consumes only 2.4 mW which is far lower than [6], [11]. Moreover, two versatile wireless communication channels are provided for W-BSN either by using cm-range 13.56 MHz inductive coupling, or 20-40 MHz BCC.…”

“…6 is one of the key building blocks in the proposed SoC which enables the high SNR TIV measurement, since a pure sinusoidal current source is difficult to realize with low power consumption and low harmonic distortion. As a result, most previous approaches were implemented either by using an external bulky sinusoidal signal generator [11], [12], or with a power consuming FPGA-based direct digital synthesizer (DDS) with low accuracy [13], [20]. To achieve both low power consumption and high signal quality, two Fully Differential Amplifiers (FDA) and an RC frequency selective network ( 120 k , 14 pF) are used to generate a 90 kHz (determined by RC time constant ) balanced sinusoidal voltage signal ( -) as shown in Fig.…”

Blood Pressure Estimation Using Pulse Transit Time From Bioimpedance and Continuous Wave Radar

“…The resulting voltage carrier signal is amplified differentially. The carrier signal is demodulated synchronously by a clock signal of 50% duty cycle and zero phase difference with respect to the sine wave [41]. The baseband signal is then amplified and converted to a single ended signal using a 3-opamp instrument amplifier (INA333), followed by an anti-aliasing lowpass RC filter.…”

An EIT Belt Reference Design with Active Electrodes and Digital Output

“…A modified band pass filter variation of a balanced differential amplifier is used similar to same purpose bioamplifiers found in literature [8,9]. The main requirement for the amplifier was to be symmetric in order to preserve the high CMRR (common mode rejection ratio) of the AFE4300 voltage input stage.…”