A Multichannel Real-Time Bioimpedance Measurement Device for Pulse Wave Analysis
ABSTRACT
Pulse wave analysis is an important method used to gather information about the cardiovascular system. Instead of detecting the pulse wave via pressure sensors, bioimpedance measurements can be performed to acquire minuscule changes in the conductivity of the tissue, caused by the pulse wave. This work presents a microcontroller-based bioimpedance measurement system, which has the capability to acquire impedance measurements from up to four independent channels simultaneously. By combining a problem-specific analog measurement circuit with a 24 bits analog-to-digital converter, the system is capable of acquiring 1000 impedances per second with a signal-to-noise ratio in a range from 92 to 96 dB. For data storage and analysis, the digitized data are sent via universal serial bus to a host PC. A graphical user interface filters and plots the data of all channels in real-time. The performance of the system regarding measuring constant impedances, as well as impedance changes over time is demonstrated. Two different applications for pulse wave analysis via multichannel bioimpedance measurements are presented. Additionally, first measurement results from a human subject are shown to demonstrate the system’s applicability of analyzing the pulse wave morphology as well as the aortic pulse wave velocity.
Existing system:
The introduced system is capable of measuring four bioimpedances simultaneously. Since for the pulse wave analysis, only the magnitude of the bioimpedance is necessary, the phase shifts are not measured by the system. The combination of an analog voltage measurement circuit and a 24 bits analog-todigital converter (ADC) enables impedance measurements with signal-to-noise ratios of up to 96 dB. Because of digitizing the bioimpedance values directly with a sample rate of 1000 samples per second (SPS), the data transfer rate to a host PC is much lower than that of raw data acquiring systems and the digital signal processing can be very elementary. Real-time filtering and plotting is performed by a developed graphical user interface (GUI) on a host PC. This work describes the development and the verification of the measurement system, as well as two exemplary measurements for pulse wave analysis.
Proposed system :
The introduced system is capable of measuring four bioimpedances simultaneously. Since for the pulse wave analysis, only the magnitude of the bioimpedance is necessary, the phase shifts are not measured by the system. The combination of an analog voltage measurement circuit and a 24 bits analog-todigital converter (ADC) enables impedance measurements with signal-to-noise ratios of up to 96 dB. Because of digitizing the bioimpedance values directly with a sample rate of 1000 samples per second (SPS), the data transfer rate to a host PC is much lower than that of raw data acquiring systems and the digital signal processing can be very elementary. Real-time filtering and plotting is performed by a developed graphical user interface (GUI) on a host PC. This work describes the development and the verification of the measurement system, as well as two exemplary measurementsfor pulse wave analysis. This work presents a microcontroller-based bioimpedance measurement system, which has the capability to acquire impedance measurements from up to four independent channels simultaneously. The digitized data are sent via universal serial bus to a host PC. A graphical user interface filters and plots the data of all channels in real-time. The performance of the system regarding measuring constant impedances, as well as impedance changes over time is demonstrated. Two different applications for pulse wave analysis via multichannel bioimpedance measurements are presented.
Software :
1. Atmel Studio 6.0.
2. MATLAB.
CONCLUSION :
This work describes the development of an embedded measurement system for acquiring four bioimpedances simultaneously. The focus of the device is the real-time measurement of minuscule changes in bioimpedances, caused by the pulse wave in the arteries. The system provides four independent impedance measurement channels, consisting of voltage controlled current sources and analog voltage measurement circuits, each. Impedance measurements in the range of up to 1000 Ω can be performed by the usage of programmable gain amplifiers. The demonstrated analog rectifier circuit is able to work with signal frequencies of up to 500 kHz. It was demonstrated, that the system has a very linear behavior and changes of impedances can be measured reliably. An SNR in a range from 92 dB to 96 dB allows to detect minuscule impedance changes in mΩ ranges.Two exemplary measurement setups are shown to demonstrate the system’s eligibility for pulse wave analyses. In the future, the system could be improved to allow a more flexible change of the excitation current frequencies and amplitudes. Additionally, the ability of phase shift and multifrequency measurements could be implemented, if there are interesting applications for it.