Influence of Strut Cross-section of Stents on Local Hemodynamics in Stented Arteries

Stenting is a very effective treatment for stenotic vascular diseases, but vascular geometries altered by stent implantation may lead to flow disturbances which play an important role in the initiation and progression of restenosis, especially in the near wall in stented arterial regions. So stent designs have become one of the indispensable factors needed to be considered for reducing the flow disturbances. In this paper, the structural designs of strut cross-section are considered as an aspect of stent designs to be studied in details. Six virtual stents with different strut cross-section are designed for deployments in the same ideal arterial model. Computational fluid dynamics（CFD） methods are performed to study how the shape and the aspect ratio（AR） of strut cross-section modified the local hemodynamics in the stented segments. The results indicate that stents with different strut cross-sections have different influence on the hemodynamics. Stents with streamlined cross-sectional struts for circular arc or elliptical arc can significantly enhance wall shear stress（WSS） in the stented segments, and reduce the flow disturbances around stent struts. The performances of stents with streamlined cross-sectional struts are better than that of stents with non-streamlined cross-sectional struts for rectangle. The results also show that stents with a larger AR cross-section are more conductive to improve the blood flow. The present study provides an understanding of the flow physics in the vicinity of stent struts and indicates that the shape and AR of strut cross-section ought to be considered as important factors to minimize flow disturbance in stent designs.

Hemodynamic change in wall shear stress in patients with coronary bifurcation lesions treated by double kissing crush or single-stent technique

Background Fluid dynamic mechanisms attributed to coronary bifurcation lesions remain a subject of study. The present study aimed at investigating the hemodynamic change of wall shear stress （WSS） in patients with coronary bifurcation lesions treated by double kissing （DK） crush or one-stent with final kissing balloon inflation （FKBI）. Methods Eighty-one patients with bifurcation lesions treated by stenting who had 3-D model reconstruction were studied. The bifurcation vessels were divided into main vessel （MV）, main branch （MB）, side branch （SB）, and polygon of confluence （POC）. MB and SB were classified by internal- and lateral-subsegments, respectively. Results The baseline magnitude of WSS in proximal MV, POC-MV, POC-MB, POC-SB and MB-internal segments increased significantly, compared to MB-lateral, SB-internal and SB-lateral. DK crush had the potential of uniformly reducing WSS, turbulent index and the WSS gradient. The WSS value at the POC-SB and SB in the one-stent group remained higher. The turbulent index and WSS gradient between the POC-SB minus the SB-lateral had equal predictive values for in-stent restenosis （ISR）. Conclusion Fluid dynamic results favor the use of DK crush over the one-stent technique.

Pore water pressure increment model for saturated Nanjing fine sand subject to cyclic loading

Three groups of dynamic triaxial tests were performed for saturated Nanjing fine sand subjected to uniform cyclic loading. The tested curves of the excess pore water pressure （EPWP） ratio variation with the ratio of the number of cycles are provided. The concept of the EPWP increment ratio is introduced and two new concepts of the effective dynamic shear stress ratio and the log decrement of effective stress are defined. It is found that the development of the EPWP increment ratio can be divided into three stages： descending, stable and ascending. Furthermore, at the stable and ascending stages, a satisfactory linear relationship is obtained between the accumulative EPWP increment ratio and natural logarithm of the effective dynamic shear stress ratio. Accordingly, the EPWP increment ratio at the number of cycles N has been deduced that is proportional to the log decrement of effective stress at the cycle number N-l, but is independent of the cyclic stress amplitude. Based on the analysis, a new EPWP increment model for saturated Nanjing fine sand is developed from tested data fitting, which provides a better prediction of the curves of EPWP generation, the number of cycles required for initial liquefaction and the liquefaction resistance.