Non-invasive Measurement Of The Electrical Property Of Blood Based On Pulse Wave Electrical Impedance Spectroscopy

There is a concrete relation between the electrical properties of blood and its components concentration pattern. The method of electrical impedance spectroscopy (EIS) using this relation to non-invasively measure the blood component has a broad prospect in medical research and practice. However,high accuracy of impedance measurement is rather difficult to acquire because of the serious influence of several factors to measurement process. These factors include experimental conditions, such as the skin-electrode interface, electrode type, and measurement position as well as the individual variations such as skin status, blood vessel pattern, blood flow, and body temperature. The concept of Pulse Wave Electrical Impedance Spectroscopy (PWEIS) is presented to reduce or eliminate the above-mentioned influences. And a novel method for non-invasive measurement of blood electrical properties is constructed on PWEIS. The method is of great prospect in non-invasive measurement of blood component and great value in medical applications.The concept of PWEIS is presented based on the model of the paralleled single blood vessel and peripheral tissue used in electrical impedance plethysmography (IPG). The relation between human impedance spectroscopy & PWEIS and blood electrical properties is theoretically deduced to analyze the principle of the influence reduction by PWEIS in impedance measurement.The principle and characteristics of electrical impedance measurement on human body is studied, and a method for measurement of PWEIS based on quadrature demodulation is presented. The experimental measurement system is constructed and tested after analysis of the performance demand for circuit modules needed in the system. High accuracy of the impedance spectroscopy and PWEIS is acquired at a wide frequency range.Characteristics of pulse wave and the adverse factors in pulse wave detection are analyzed, and the calculation method of PWEIS in frequency domain is studied. The optimal length of pulse wave data is investigated using DFT. Outliers in the pulse wave signal is diminished using wavelet method.Parallel electrical impedance model of forearm and serial electrical impedance model of earlobe is built up according to their anatomy and the current and voltage distributions in the models are calculated using finite element method (FEM). Experimental measurement is conducted on several subjects and the impedance spectroscopy and PWEIS is acquired. The results show that the models comprehensively describe the electrical prosperities of the forearm and the earlobe. The individual variations cannot be completely eliminated by the PWEIS of forearm because of its parallel impedance of the tissues in forearm. And Earlobe PWEIS can reduce the individual variation influences to a rather low level and makes non-invasive measurement of blood electrical properties practically possible.