Hemodynamic Analysis of Coronary Circulation in Angulated Coronary Stenosis Following Stenting

The present study in angulated coronary stenosis used human in vivo hemodynamic parameters and computed simulation, both qualitatively and qualitatively, to evaluate the influence of flow velocity and wall shear stress (WSS) on coronary atherosclerosis, the changes of hemodynamic indices following coronary stenting, and their effect on evolving in-stent restenosis. Initial and follow-up coronary angiographies in patients with angulated coronary stenosis were performed (n=60). The optimal degree of coronary stenting for angulated coronary stenosis had two models, the less than 50% angle changed group (model 1, n=33) and the more than 50% angle changed group (model 2, n=27). This angle change was based on the percentage change of vascular angle between pre- and post-intracoronary stenting. The flow-velocity wave obtained from in vivo intracoronary Doppler study data was used for in vitro numerical simulation. Spatial and temporal patterns of the flow-velocity vector and recirculation area were drawn throughout the selected segment of coronary models. WSS of pre- and post-intracoronary stenting was calculated from three-dimensional computer simulation. As results, follow-up coronary angiogram demonstrated significant difference in the percentage of diameter stenosis between the two groups (group 1: 40.3 +/- 30.2 vs. group 2: 25.5 +/- 22.5%, p < 0.05). Negative shear area on 3D simulation, which is consistent with the re-circulation area of flow vector, was noted on the inner wall of the post-stenotic area before stenting. The negative WSS disappeared after stenting. High spatial and temporal WSS before stenting fell within the range of physiologic WSS after stenting. This finding was more prominent in model 2 (p < 0.01). The present study suggests that hemodynamic forces exerted by pulsatile coronary circulation, termed WSS, might affect the evolution of atherosclerosis within the angulated vascular curvature. Moreover, geometric characteristics, such as the angular difference between pre- and post- intracoronary stenting might define optimal rheologic properties for vascular repair after stenting.

Development of the Unsteady Capillary Tube Viscometer and Viscosity Measurement of Blood Analogue Fluid

The purpose of the present study is to measure the viscosity of liquid in the capillary tube viscometer using the unsteady flow concept. The capillary tube viscometer is consisted of a small cylindrical reservoir, capillary tubes, and the mass flow rate measuring system interfaced with computer. Two capillary tubes with 1.152 and 3.002 mm (inner diameter) are used to determine the diameter effects on the viscosity measurements. The instantaneous shear rate and gravitational driving force in the capillary tube are determined by measuring the mass flow rate through the capillary tube instantaneously. The measured viscosities of water and aqueous Separan solution as the blood analogue fluid are in good agreement with the reported experimental data.

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.

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.