Hemodynamic Effects on Atherosclerosis-Prone Coronary Artery: Wall Shear Stress / Rate Distribution and Impedance Phase Angle in Coronary and Aortic Circulation

The objective of the present study was to evaluate the hemodynamic characteristics of an atherosclerosis-prone coronary artery compared to the aorta. We describe three- dimensional spatial patterns of wall shear stress (WSS) according to the impedance phase angle in pulsatile coronary and aorta models using in vivo hemodynamic parameters and computed numerical simulations both qualitatively and quantitatively. Angiography of coronary arteries and aortas were done to obtain a standard model of vascular geometry. Simultaneously to the physiologic studies, flow-velocity and pressure profiles from in vivo data of the intravascular Doppler and pressure wire studies allowed us to include in vitro numerical simulations. Hemodynamic variables, such as flow-velocity, pressure and WSS in the coronary and aorta models were calculated taking into account the effects of vessel compliance and phase angle between pressure and flow waveforms. We found that there were spatial fluctuations of WSS and in the recirculation areas at the curved outer wall surface of the coronary artery. The mean WSS of the calculated negative phase angle increased in the coronary artery model over that in the aorta model and the phase angle effect was most prominent on the calculated amplitude of WSS of the coronary artery. This study suggests that the rheologic property of coronary circulation, such as the fluctuation of WSS/WSR induces several hemodynamic characteristics. A separation of flow-velocity, a difference in phase between pressure conductance and blood flow and prominent temporal and/or spatial oscillatory fluctuations of the shear forces as a function of pulsatile flow might be important factors in atherogenesis and progression of atherosclerosis.

Fundamental Study for Simulation of Blood Cell Motion in a Blood Vessel

PURPOSE: The objective of this study is to investigate the blood cell motion in human capillary by applying the boundary singularity method. METHODS: A particle motion of spherical shape falling in a vertical tube filled with Newtonian fluid is studied by using the boundary singularity method and the experiment. RESULTS AND CONCLUSION: As the eccentric ratio increases up to 0.6, the rotational velocity increases almost linearly and the falling velocity remains constant. However, as the eccentric ratio exceeds 0.6, the rotational velocity increases rapidly and the falling velocity decreases. As the tube radius increases, falling velocity increases and approaches the stokes velocity and the rotational velocity decreases.

Fundamental Study for Simulation of Blood Cell Motion in a Blood Vessel

PURPOSE: The objective of this study is to investigate the blood cell motion in human capillary by applying the boundary singularity method. METHODS: A particle motion of spherical shape falling in a vertical tube filled with Newtonian fluid is studied by using the boundary singularity method and the experiment. RESULTS AND CONCLUSION: As the eccentric ratio increases up to 0.6, the rotational velocity increases almost linearly and the falling velocity remains constant. However, as the eccentric ratio exceeds 0.6, the rotational velocity increases rapidly and the falling velocity decreases. As the tube radius increases, falling velocity increases and approaches the stokes velocity and the rotational velocity decreases.

Morphological Changes of the Endothelial Cell under the Influence of the Hemodynamic Stresses

PURPOSE: The objective of this study is to investigate the effects of hemodynamics on morphological changes of human endothelial cells. METHODS: The changes under the laminar flow condition are investigated by the in-vitro experiment and computer simulation. Micrographs of the endothelial cells in the laminar flow chamber are taken as a function of the exposed time. Idealized geometric shapes of the cells whose shapes are changing with the exposed time due to the flow stresses are portrayed by the computer simulation. Drag force on the cell due to the pressure and shear stress is calculated for two constraining conditions, that is, the cell changes its shape keeping its initial volume or initial surface area. RESULTS AND CONCLUSION: The drag force of the cell which keeps constant volume is smaller than that of the cell which keeps constant surface area.

Morphological Changes of the Endothelial Cell under the Influence of the Hemodynamic Stresses

PURPOSE: The objective of this study is to investigate the effects of hemodynamics on morphological changes of human endothelial cells. METHODS: The changes under the laminar flow condition are investigated by the in-vitro experiment and computer simulation. Micrographs of the endothelial cells in the laminar flow chamber are taken as a function of the exposed time. Idealized geometric shapes of the cells whose shapes are changing with the exposed time due to the flow stresses are portrayed by the computer simulation. Drag force on the cell due to the pressure and shear stress is calculated for two constraining conditions, that is, the cell changes its shape keeping its initial volume or initial surface area. RESULTS AND CONCLUSION: The drag force of the cell which keeps constant volume is smaller than that of the cell which keeps constant surface area.

Analysis of Hemodynamic Characteristics in End-to-Side Anastomoses with Miller Cuff

The hemodynamic characteristics of the cuff end-to-side anastomosis model are investigated using by the finite volume predictions. The flow rates and the impedance indices through of the cuff anastomosis model are compared with those of the anastomosis model without the cuff. Blood flow increased through the cuff anastomosis model than the standard anastomosis model. The impedance index decreased with the increase of flow rate. The impedance index at a given flow rate is reduced by the increase of anastomosis angle and further reduced by the addition of the cuff. The results suggest that the cuff anastomosis model should be applied for the low Reynolds number flow and/or the small artery anastomosis model.

Visualization of Pulsatile Flow of the Blood Substitute Fluids Using the Particle Image Velocimetry

PURPOSE: The objective of the present study is to investigate the steady and pulsatile flow phenomena of the blood substitute fluids in the circular and bifurcated vessels numerically and experimentally. METHODS: The particle image velocimetry (PIV) is adopted to visualize the flow fields in the circular and bifurcated vessels. In order to analyse the complex flow phenomena of the blood substitute fluids in the bifurcated vessel, the constitutive equations which are suitable to describe the rheological properties of the non-Newtonian fluids are determined and the steady and unsteady momentum equations are solved by the finite volume prediction. RESULTS AND CONCLUSION: Velocity vectors of the steady flow in the bifurcated tube obtained by the PIV system are in good agreement with those obtained by the numerical analysis. The experimental and numerical results show the recirculation zone in the outer wall distal to bifurcation.

Modelling of Elastic Blood Vessel under the Pulsatile Flow

PURPOSE: Characteristics of pulsatile flow in 3-dimensional arterial geometry and elastic vessel wall should be investigated in order to understand the physiological blood flow in human body. In this study, the modelling of the physiological blood flow in the elastic blood vessel is proposed. METHODS: The finite volume predictions are used to analyse the pulsatile flow characteristics in the elastic blood vessel. RESULTS AND CONCLUSION: Variations of the pressure and the velocity waveforms are obtained using the proposed modelling. The magnitudes of the pressure waveforms in the elastic blood vessel model are bigger than those of the rigid blood vessel model.

Analysis of Hemodynamic Characteristics in Anastomotic Sites of Femoral Artery Implantation

The objective of the present study is to obtain information on the hemodynamic characteristics in the anastomotic sites of femoral artery through the vascular implantation. Three dimensional steady and physiological blood flows in the femoral artery are simulated using the finite volume method. The geometrical shape of the anastomotic sites is made based on the vascular anatomy of a white rabbit. Wall shear stress distributions in the anastomotic sites for the physiological flow are compared with those for steady flow. Blood flow phenomena in the anastomotic sites of the femoral artery are discussed extensively.

Effect of Physical Vibration on Blood Viscosity

The objective of the current study is to investigate the effect of physical vibration on blood viscosity. The "capillary tube viscometer concept" is applied to measure blood viscosity. Blood viscosity can be measured at the minimum shear rate of 12 s(-1) by the capillary tube viscometer. To examine the effect of physical vibration on blood viscosity, the vibrations are produced by contact with an electronic speaker. The frequencies of vibration are varied from 0 to 1000 Hz. The experimental results show that blood viscosity can be effectively reduced by applying vibration. Blood viscosity decreases as much as 10~12 % by applying vibration.

Computed numerical analysis of the biomechanical effects on coronary atherogenesis using human hemodynamic and dimensional variables

The objectives of this investigation were to evaluate biomechanical factors in the atherosclerotic process using human in vivo hemodynamic parameters and computed numerical simulation qualitatively and quantitatively. The three-dimensional spatial patterns of steady and pulsatile flows in the left coronary artery were simulated, using a finite volume method. Coronary angiogram and Doppler ultrasound measurement of the proximal left coronary flow velocity were performed in humans. Inlet wave velocity distribution obtained from in vivo data of the intravascular Doppler study allowed for input of in vitro numerical simulation. Hemodynamic variables, such as flow velocity, pressure and shear stress of the left anterior descending coronary bifurcation site were calculated. We found that there were spatial fluctuation of flow-velocity and recirculation areas at the curved outer wall of the left anterior descending coronary artery, which were due to the differences of flow-velocity and shear stress, especially during the declaration phase of pulsatile flow. This study suggests that rheologic properties may be a part of the atherogenic process in the coronary bifurcated and curved areas.