A Method For Detecting Hemodynamic Variables In Common Carotid Artery By Integrating Bioelectrical Impedance Technique

Hemodynamic variables such as blood flow velocity,shear stress,vascular compliance,and peripheral resistance not only play an important role in regulating the function and structure of vessels,but are also important physiological indicators for evaluating cardiovascular and cerebrovascular functions.Exercise training can change hemodynamic variables directly,and help prevent or treat cardiovascular and cerebrovascular diseases.The common carotid artery is an important blood-supplying organ that connects the upstream heart and the downstream cerebrovascular bed.Accurate detection of hemodynamic variables of the common carotid artery has clinical significance for early diagnosis of cardiovascular and cerebrovascular diseases.The detection methods of hemodynamic variables in the common carotid artery includes color Doppler ultrasound,computed tomography and magnetic resonance imaging.These detection techniques yield high resolution and accuracy,but can be expensive and bulky,making online detection is difficult.Bioelectrical impedance technique may be used to improve the portability and miniaturize the detection equipment,thereby facilitating real-time and continuous detection during exercise.However,affected by factors including tissues surrounding the common carotid artery and the pulsatile blood flow,the quantitative relationship between bioelectrical impedance signal of the neck and the hemodynamic variables of common carotid artery has not been fully understood.This thesis introduces a method by combining modeling,numerical simulation and exercise intervention experiment to non-invasively evaluate the hemodynamic variables in the common carotid artery and its afterload.The main research contributions are summarized here:(1)The ‘local flow' theory of Ling & Atabek for pulsatile flow in an elastic artery and Maxwell-Fricke equations for suspension conductivity are used to obtain the quantitative relationship between blood flow conductivity,electrical impedance signal with the center-line velocity and the diameter of the common carotid artery.Then,a five-element lumped parameter model is introduced to describe the afterload input impedance of common carotid artery.Lastly,a method for solving the local and the afterload hemodynamic variables of the common carotid artery through blood flow electrical impedance and center-line velocity is established.(2)By considering the influence of the complex biological tissues surrounding the common carotid artery,a simplified 3D model of the human neck structure is built to describe the non-linear relationship between blood flow impedance in the common carotid artery and the human neck impedance.Meanwhile,a numerical simulation is carried out to obtain the spatial distribution of the electric field in the neck model under various detection and physiological conditions.The impedance value of the neck model under various detection conditions is also calculated.The impedance change rate(ICR)is introduced as an evaluation index for the best position of attaching electrodes.(3)A portable acquisition device of electrical impedance signals is designed and developed.The device contains composed of four parts: a generator of the excitation signals,an acquisition of the voltage and current signals,DSP signal processing and control,and auxiliary circuits.The proposed electrical impedance signals acquisition device can overcome high common-mode interference of the human body and improve the acquisition resolution of bioelectrical impedance signals.(4)An acute aerobic exercise intervention experiment is performed to verify the detection method.The diameter of common carotid artery before exercise,the physiological information such as center-line velocity in the common carotid artery,blood pressure in the brachial artery and the neck impedance are measured by the acquisition device before and after exercise.The local and afterload hemodynamic variables in common carotid artery after exercise such as the diameter,blood pressure,blood flow,shear stress,peripheral resistance,compliance and inertia of downstream cerebrovascular bed are calculated.The results show that the detection method can achieve a real-time,non-invasive evaluation of hemodynamic variables in the common carotid artery and its afterload.In summary,the hemodynamic detection method by integrating the bioelectrical impedance technique is introduced in this paper.The work not only provides a theoretical framework for real-time and continuous detecting the hemodynamic variables in common carotid artery,but also provides technical foundations to support the development of wearable,portable and miniaturized detection equipment.