Hemodynamic Modeling And Analysis Of The Conductivity And Electrical Impedance Of Arterial Blood Flows

Hemodynamic parameters,including cardiac output,blood flow velocity,arterial diameter,arterial elastic modulus,peripheral resistance and wall shear stress,play important roles in the occurrence and development,the early prevention and the evaluation of therapeutic effects of cardiovascular and cerebrovascular diseases.In clinical practice,these hemodynamic parameters are usually detected and analyzed by combining CT/MRI imaging with ultrasonic Doppler blood flow-meter.However,the bulkiness and high cost of these detection devices hinders the online monitoring of hemodynamic parameters of individuals in daily life or during exercise trainings.In contrast,Bio-electrical impedance technology demonstrates the advantages of low cost,simple operation,wearability and superior continuous detection performance.Hence,the technique has been applied in the evaluation of cardiovascular and cerebrovascular functions and the early diagnosis of diseases.To date,the quantitative relationship between arterial blood flow conductivity,electrical impedance and hemodynamic parameters such as arterial diameter,blood flow velocity has not been fully explored,thus posing a challenge to the wide use of this technique in monitoring hemodynamic parameters of individuals in daily life or during exercise trainings.In this thesis,by using theoretical modeling and experimental verification methods,the quantitative relationship between arterial blood flow conductivity,electrical impedance and arterial hemodynamic parameters was investigated.Through exercise interventions,the key hemodynamic parameters affecting arterial blood flow conductivity and electrical impedance were analyzed.The thesis provides a methodology basis for online monitoring arterial hemodynamic parameters.The main contents and results of the thesis are as follows:(1)Considering the effect of the elastic deformation of arterial wall on the conductivity of arterial blood flow,I proposed a theoretical model to investigate the quantitative relationship between center-line velocity,arterial radius and the conductivity,electrical impedance of arterial blood flow,in combination with the "local flow" theory of Ling&Atabek for hemodynamics of pulsatile flow in elastic artery with the Maxwell-Fricke equation for the suspension conductivity.Furthermore,I developed a circulatory device and a measuring system for electrical impedance of arterial blood flow,then experiments in vitro were conducted to verify the correctness of the theoretical model.(2)Based on the data of arterial blood flow electrical impedance and conductivity calculated with the theoretical model,a simplified mathematical model was proposed to characterize the quantitative relationship between electrical conductivity and center-line velocity,arterial radius.The proposed model quantitatively illustrated the independent contribution of center-line velocity and arterial radius to the conductivity and electrical impedance of arterial blood flow,confirming that the conductivity and electrical impedance of the arterial blood flow were determined by the center-line velocity and the arterial radius,respectively.The model provided a new approach for the reverse calculation of center-line velocity and arterial radius waveforms by using the detected conductivity and electrical impedance of arterial blood flow,thus enabling the calculation of hemodynamic parameters such as flow rate and wall shear stress.(3)By means of acute exercise intervention,hemodynamic analysis,statistics and correlation analysis,the variation of carotid artery radius,center-line velocity,blood flow conductivity and electrical impedance before and after acute exercise were studied.Moreover,the relationship between arterial blood flow conductivity,electrical impedance and arterial radius,center-line velocity were investigated.The results showed that,the amplitude of arterial radius decreased with the increase of exercise load,and the amplitude of center-line velocity,arterial blood flow conductivity and electrical impedance increased with the rise of exercise load.There a high correlation between arterial blood flow conductivity and center-line velocity,and the electrical impedance of arterial blood flow was highly correlated with the arterial radius,indicating that the electrical conductivity waveform before and after exercise was determined by the center-line velocity waveform before and after exercise,while the electrical impedance waveform before and after exercise relied on the arterial radius waveform before and after exercise,respectively.This rule was still applicable under the physiological conditions of exercise.These results provided a new method for the regulation of cardiovascular and cerebrovascular functions by monitoring exercise intervention through electrical impedance signal of arterial blood flow.In conclusion,based on the principle of hemodynamics,the thesis established a theoretical model of arterial blood flow conductivity and electrical impedance for pulsatile flow in elastic tubes.The theoretical model was verified by in vitro experiments.The key hemodynamic factors affecting the electrical conductivity and impedance of arterial blood flow were clarified by establishing a simplified mathematical model combined with correlation analysis.The changes of carotid artery radius,center-line velocity,blood flow conductivity and electrical impedance before and after acute exercise intervention were studied.This thesis also presented a novel method for evaluating hemodynamic parameters by monitoring the electrical impedance signal of arterial blood flow.The research results are of theoretical and practical values in making early diagnosis and screening of cardiovascular and cerebrovascular diseases,as well as evaluating rehabilitation with the aid of electrical impedance technique.