Liu Zhaorong

An analysis model of pulsatile blood flow in arteries

Blood flow in artery was treated as the flow under equilibrium state (the steady flow under mean pressure) combined with the periodically small pulsatile flow. Using vascular strain energy function advanced by Fung, the vascular stress-strain relationship under equilibrium state was analyzed and the circumferential and axial elastic moduli were deduced that are expressed while the arterial strains around the equilibrium state are relatively small, so that the equations of vessel wall motion under the pulsatile pressure could be established here. Through solving both the vessel equations and the linear Navier-Stokes equations, the analytic expressions of the blood flow velocities and the vascular displacements were obtained. The influence of the difference between vascular circumferential and axial elasticities on pulsatile blood flow and vascular motion was discussed in details.

Feature Extraction for Pulse Waveform in Traditional Chinese Medicine by Hemodynamic Analysis

Pulse diagnosis is one of important diagnosis methods in Traditional Chinese Medicine(TCM). Feature extraction of TCM pulse has received more and more attention in recent years. While most of previous methods for feature extraction of TCM pulse have no specific correlation with the mechanism of TCM pulse, a hemodynamics method was used to calculate the pulse waveform velocity(PWV) and pulse reflection factor(R) , which reflected the principle of TCM pulse diagnosis. The results showed that the PWV and R are significantly different among four TCM pulses including normal pulse, slippery pulse, wiry pulse and wiry-slippery pulse. It is concluded that the PWV and R may be used as the features for the classification of TCM pulses.

Displacement wave of the blood vessel —A mechanical model

According to clinical observations and model experiment, we have developed a theoretical model and obtained its mathematical equations to investigate the displacement wave of the blood vessel. The waveform and its occurrence criterion have been obtained by using perturbation theory and numerical method. The present study suggests that the displacement wave is associated with the blood velocity waveform and the machanical behaviour of the blood vessel, but not with the pressure waveform. The clinical criterion is in agreement with the observations.

The effects of blood viscoelasticity on the pulse wave in arteries

Based on Womersleys theory, the frequency equation satisfied by a complex wave velocity of a pulse wave in arteries was generalized to viscoelastic blood, a general formula of the complex wave velocity with regard to both linearly viscoelastic arteries and linearly viscolelastic blood was obtained, and the effects of the viscoelastic property of blood on the phase velocity and the wave attenuation of the pulse wave using the formula systematically was discussed. It is concluded that the influence of the blood elasticity on the wave propagation of a pulse wave in arteries is weaker than that of the arterial viscosity and may be neglected in larger arteries.

On analysis of the steady flow in an irrectangular parallel-plate flow chamber

The parallel-plate flow chamber (PPFC), of which the height is far smaller than its own length and width, is one of the main apparatus for the in vitro study of the mechanical behaviors of cultured cells at the bottom of PPFC undergoing shear stress. The PPFC of which the upper and lower plates are rectangular is usually used by research workers, and the flow field in this kind of PPFC (except for the regions near the entrance and exit) is uniform[1], so only the effect the shear stress with one value has on cultured cells can be observed during each experiment. A kind of PPFC of which the upper and lower plates are not rectangular is proposed in this paper. The distributions of the velocities inside and the shear stresses at the bottom of the chamber are given by analyzing the flow field of the steady flow in the PPFC. The results show that the mechanical behaviors of cultured cells undergoing the shear stresses with various may be simultaneously observed by the use of this kind of irrectangular PPFC. The theoretical and experimental results obtained by Ultrasonic Doppler Technique show good agreement.

Analysis of oscillatory flow in consideration of a plasma layer in arterial stenoses

This paper presents the influences of plasma layer on the oscillatory flow in arterial stenosis. The analysis demonstrates that the existence of the plasma layer may obviously change the characteristics of flow such as velocity-profiles, longitudinal impedance and pressure gradient, but hardly change the phase of longitudinal impedance and pressure gradient. Besides, such influences vary with α and degree of stenosis. These analyses have special physiological significance in blood circulation system.

Dynamic principle for interaction between heart and arterial system

Various steady models for interaction between heart and arterial system have been given in literature. In our recent study, a dynamic principle, i.e. the principle of least cardiac work is proposed, and a dynamic model for interaction of heart and arterial system is established. Preliminary results of our experiments show that both the principle and the model are consistent with the physiological phenomena. It reveals that the present analysis may offer a new measure for the study of dynamic process of interaction between heart and arterial system.

A COUPLING MODEL OF LEFT VENTRICLE AND ARTERIAL SYSTEM

A simple left ventricular model and a systemic arterial model of a tapered tube with eight branches are used in this paper which are combined into a mathematical coupling model of heart and arterial system to study the interaction of the heart and the arterial system.

A computer model of pulse wave and input impedance in human arteries

To predict the propagation of pressure and flow pulses in arterial system and the variation of vascular input impedance, a branched and tapered tube model is studied through one-dimensional transient flow analysis. Coupling the continuity and momentum equations yields a group of quasilinear hyperbolic partial differential equations which can be solved numerically by using the method of characteristics. Several boundary conditions of the arterial system are also simplified suitably.The propagation of the pulses of the arterial system and the vascular input impedance is calculated on computer by using the dimensions and the physiological data of the arterial system. The results point out that the pressure and flow pulses of the arterial system and the vascular input impedance produced by this theoretical model is consistent quite well with the experimental results published.

The effects of external counterpulsation on the pulse waves in human aorta

A five-branch-tube model simulating human systemic circulation system is proposed to analyze the effects of External Counterpulsation (ECP) on the pulse waves in human aorta. The results derived from the model demonstrate that the pressure and flow waves in aorta could be changed when ECP is in operation, and the results are approximately in agreement with the experiment results by five-branch-tube simulation system. It provides an effective way to define the actual operation of ECP so as to get an optimal therapeutic effect.