Design Of A Sphygmus Impedance Spectroscopy Measurement System Based On FPGA

The pulse waves contains abundant physiological and pathological information of the cardiovascular system.The traditional bioimpedance spectroscopy(BIS)pulse waves measurement is based on the theory of Impedance Plethysmograph(IPG).By using backward measuring method,it is not only time-consuming but also inefficient,which can barely reflect real-time impedance characteristics.What’s more,it can hardly perform the advantage of BIS by ignoring the frequency-domain analysis.Therefore,it is important to establish new testing methods and measurement systems.In this thesis,an improved method to record the pulse waves impedance spectrum by combining time and frequency domain is presented.Based on FPGA platform,a BIS ultrafast measuring system is designed for pulse waves measurement.The main study is as follows.1.Importance of Pulse waves Measurement StudyThe principle of pulse waves generation and the relationship between the characteristic points and cardiovascular system information are introduced.Conventional pulse waves measurement methods are compared.The limitation of the traditional BIS pulse waves analysis theory and method based on IPG theory is introduced in detail.2.Study of Improved Time-Frequency-Domain Pulse waves Measurement MethodBased on models of blood impedance and models of human pulsating position blood vessel impedance,a new pulse waves recording method which combines time and frequency domain is proposed according to the mathematical relations between excitation frequency changes,pulsating volume changes and IPG measured by BIS.Pulse waves in time domain can reflect the characteristic points,time parameter and other sphygmus informantion.The pulse waves in frequency domain can reflect the parameters of pulsating hemodynamic characteristics and further information of human cardiovascular system can be read.3.Study of BIS Ultra-Fast Measurement SystemBy analysing the basic principle of traditional BIS measurement and its disadvantages,a kind of BIS ultra-fast measurement system based on FPGA and peripheral digital-analog circuit is designed.In the new system,the multi-frequency sinusoidal signal(Multisine)is used as the excitation signal and the frequency range covers all the necessary frequency range of BIS(10KHz-1MHz).The method of synchronizing sampling in whole period avoids the spectrum leakage in the Fourier transform processing of the sampling sequence.The excitation signal generation,sampling signal FFT transformation and CORDIC method impedance spectrum fitting can be carried out by FPGA.By using the improved system,the BIS information at hundreds of excitation frequency points can be obtained in one sampling period.Thus,the BIS measurement can be completed one thousand times per second.4.Verification of the Measurement SystemThe precision standard impedance meter(WK6500B)is used to calibrate the designed measurement system.A resistor-capacitor model is constructed to evaluate the calibrated measurement system.The results show the usability of the designed measurement system.In this thesis,the time-frequency combined pulse waves recording method provides a new direction of pulse waves study.The BIS ultra-fast measurement system based on FPGA can accomplish the fast measurement and fitting of impedance spectrum and has practical significance for miniaturization and marketization of BIS instruments.