@article{hyun_kleinstreuer_archie_2003, title={Computational analysis of effects of external carotid artery flow and occlusion on adverse carotid bifurcation hemodynamics}, volume={37}, ISSN={["0741-5214"]}, DOI={10.1016/S0741-5214(02)75326-3}, abstractNote={This is a computational analysis of the effects of external carotid artery (ECA) flow, waveform, and occlusion geometry on two hemodynamic wall parameters associated with intimal hyperplasia and atherosclerosis. Transient three-dimensional fluid mechanics analysis was applied to a standard carotid artery bifurcation. Mean internal carotid artery (ICA) flow was maintained at 236 mL/min with a normal waveform. ECA flow was increased from zero to 151 mL/min (64% of ICA flow) with both a normal biphasic waveform and a damped waveform. Geometry of five ECA occlusions was studied: distal, proximal stump, smooth, smooth without carotid sinus, and optimal reconstruction. Two time-averaged and area-averaged hemodynamic wall parameters were computed from the velocity and wall shear stress (WSS) solutions, ie, wall shear stress angle gradient (WSSAG) and oscillatory shear index (OSI). Both local and area-averaged hemodynamic wall parameters were computed for the distal common carotid artery (CCA) and the proximal ICA. When ECA flow with a normal waveform is increased from zero to 151 mL/min, area-averaged WSS values increase in the CCA, from 3.0 to 4.4 dynes/cm2 (46%), and in the ICA, from 16.5 to 17.1 dynes/cm2 (4%); minimum local WSS values in the carotid sinus remain less than 1 dyne/cm2; maximum local values of WSSAG and OSI are observed in the carotid sinus and increase from 3.5 to 9.1 radian/cm (160%) and 0.23 to 0.46 (100%), respectively; CCA plus ICA area-averaged WSSAG increases by 52%, and OSI increases by 144%; and damping of the ECA waveform has little effect on local or area-averaged WSSAG but reduces OSI to 68%. When the ECA is occluded, the minimum local WSS in the carotid sinus is less than 1 dyne/cm2. However, if the carotid sinus is removed or the CCA-ICA geometry hemodynamically optimized, the minimum WSS is approximately 4 dynes/cm2. Similarly, eliminating the carotid sinus markedly reduces local maximum WSSAG, from 3.0-3.5 radian/cm to 0.3 radian/cm, and reduces local maximum OSI from 0.22-0.49 to 0.04. Area-averaged WSSAG and OSI over the CCA and ICA are reduced by approximately 50% with elimination of the carotid sinus. The degree of adverse carotid bifurcation hemodynamics as measured with WSSAG and OSI is directly proportional to ECA flow. The marked difference in normal ICA and ECA flow waveforms does not contribute to adverse wall hemodynamics. Location of an ECA occlusion (distal, proximal, stump, smooth) does not affect adverse carotid hemodynamics; however, marked improvement is obtained with elimination of the carotid sinus.}, number={6}, journal={JOURNAL OF VASCULAR SURGERY}, author={Hyun, S and Kleinstreuer, C and Archie, JP}, year={2003}, month={Jun}, pages={1248–1254} }
 @article{longest_kleinstreuer_archie_2003, title={Particle hemodynamics analysis of Miller cuff arterial anastomosis}, volume={38}, ISSN={["0741-5214"]}, DOI={10.1016/S0741-5214(03)00950-9}, abstractNote={Studies of animal and human below-knee anastomoses with Miller cuffs indicate that improved graft patency results from redistribution of intimal hyperplasia away from areas critical to flow delivery, such as the arterial toe. We hypothesize that particle hemodynamic conditions are a biophysical mechanism potentially responsible for the clinically observed shift in intimal hyperplasia localization associated with better patency of the Miller configuration.Computational fluid dynamics analysis of vortical flow patterns, wall shear stress fields, and potential for platelet interaction with the vascular surface was performed for realistic three-dimensional conventional and Miller cuff distal end-to-side anastomoses. Sites of significant platelet-wall interaction, including elevated near-wall particle concentrations and stasis, were identified with a validated near-wall residence time model, which includes shear stress-based factors for particle activation and surface reactivity.Particle hemodynamics largely coincide with the observed redistribution of intimal hyperplasia away from the critical arterial toe region. Detrimental changes in wall shear stress vector magnitude and direction are significantly reduced along the arterial suture line of the Miller cuff, largely as a result of increased anastomotic area available for flow redirection. However, because of strong particle-wall interaction, resulting high near-wall residence time contours indicate significant intimal hyperplasia along the graft-vein suture line and in the vicinity of the arterial heel.While a number of interacting mechanical, biophysical, and technical factors may be responsible for improved Miller cuff patency, our results imply that particle hemodynamics conditions engendered by Miller cuff geometry provide a mechanism that may account for redistribution of intimal hyperplasia. In particular, it appears that a focal region of significant particle-wall interaction at the arterial toe is substantially reduced with the Miller cuff configuration.}, number={6}, journal={JOURNAL OF VASCULAR SURGERY}, author={Longest, PW and Kleinstreuer, C and Archie, JP}, year={2003}, month={Dec}, pages={1353–1362} }
 @article{hyun_kleinstreuer_archie_2001, title={Computational particle-hemodynamics analysis and geometric reconstruction after carotid endarterectomy}, volume={31}, ISSN={["0010-4825"]}, DOI={10.1016/S0010-4825(01)00007-5}, abstractNote={Transient three-dimensional laminar incompressible dilute suspension flow in rigid in-plane carotid artery bifurcations has been solved with a user-enhanced finite-volume program. Instantaneous velocity vector and wall shear stress vector fields illustrate strong "disturbed flow" patterns. Implications of elevated surface contours of hemodynamic wall parameters, indicating such disturbed flows, and particle deposition sites are discussed and a relative comparison in terms of indicator functions between the endarterectomized carotid artery bifurcation and two design improvements is shown. Although the combined perioperative mortality and non-fatal stroke rate for carotid endarterectomy ranges only from 2% to 7%, the final geometric design recommendation presented merits consideration because it may significantly lower the chances of post-operative complications such as stroke, ischemic attack, or even death. The new carotid artery bifurcation design is based on the overall reduction of "disturbed flow" indicator functions, including the time-averaged wall shear stress angle deviation and a wall deposition parameter for critical blood particles, such as monocytes.}, number={5}, journal={COMPUTERS IN BIOLOGY AND MEDICINE}, author={Hyun, S and Kleinstreuer, C and Archie, JP}, year={2001}, month={Sep}, pages={365–384} }
 @article{kleinstreuer_hyun_buchanan_longest_archie_truskey_2001, title={Hemodynamic parameters and early intimal thickening in branching blood vessels}, volume={29}, DOI={10.1615/critrevbiomedeng.v29.i1.10}, abstractNote={Intimal thickening due to atherosclerotic lesions or intimal hyperplasia in medium to large blood vessels is a major contributor to heart disease, the leading cause of death in the Western World. Balloon angioplasty with stenting, bypass surgery, and endarterectomy (with or without patch reconstruction) are some of the techniques currently applied to occluded blood vessels. On the basis of the preponderance of clinical evidence that disturbed flow patterns play a key role in the onset and progression of atherosclerosis and intimal hyperplasia, it is of interest to analyze suitable hemodynamic wall parameters that indicate susceptible sites of intimal thickening and/or favorable conditions for thrombi formation. These parameters, based on the wall shear stress, wall pressure, or particle deposition, are applied to interpret experimental/clinical observations of intimal thickening. Utilizing the parameters as "indicator" functions, internal branching blood vessel geometries are analyzed and possibly altered for different purposes: early detection of possibly highly stenosed vessel segments, prediction of future disease progression, and vessel redesign to potentially improve long-term patency rates. At the present time, the focus is on the identification of susceptible sites in branching blood vessels and their subsequent redesign, employing hemodynamic wall parameters. Specifically, the time-averaged wall shear stress (WSS), its spatial gradient (WSSG), the oscillatory shear index (OSI), and the wall shear stress angle gradient (WSSAG) are compared with experimental data for an aortoceliac junction. Then, the OSI, wall particle density (WPD), and WSSAG are segmentally averaged for different carotid artery bifurcations and compared with clinical data of intimal thickening. The third branching blood vessel under consideration is the graft-to-vein anastomosis of a vascular access graft. Suggested redesigns reduce several hemodynamic parameters (i.e., the WSSG, WSSAG, and normal pressure gradient [NPG]), thereby reducing the likelihood of restenosis, especially near the critical toe region.}, number={1}, journal={Critical Reviews in Biomedical Engineering}, author={Kleinstreuer, C. and Hyun, S. and Buchanan, J. R. and Longest, P. W. and Archie, J. P. and Truskey, G. A.}, year={2001}, pages={1–64} }
 @article{archie_2001, title={Presidential address: A brief history of arterial blood flow - from Harvey and Newton to computational analysis}, volume={34}, ISSN={["0741-5214"]}, DOI={10.1067/mva.2001.116108}, abstractNote={Mathematicians, engineers, physicians, and vascular surgeons have all contributed to understanding blood flow in arteries. The common thread has been the ability to measure or calculate blood flow and pressure. I was profoundly influenced by the requirement of quantitative, accurate, and precise measurements by both Julien Hoffman, who taught me basic vascular research, and John Kirklin, who taught me clinical research and the mental and technical skills necessary to operate effectively and efficiently. This is illustrated by the words of Lord Kelvin: “When you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it or express it in numbers, your knowledge is of a meager and unsatisfactory kind.”}, number={3}, journal={JOURNAL OF VASCULAR SURGERY}, author={Archie, JP}, year={2001}, month={Sep}, pages={398–404} }
 @article{hyun_kleinstreuer_archie_2000, title={Computer simulation and geometric design of endarterectomized carotid artery bifurcations}, volume={28}, ISSN={["0278-940X"]}, DOI={10.1615/critrevbiomedeng.v28.i12.100}, abstractNote={The main goal of this computational study is to establish surgical guidelines for optimal geometries of carotid endarterectomy reconstructions that may measurably reduce postoperative complications, that is, thrombosis, stroke, and/or restenosis. The underlying hypotheses are that nonuniform hemodynamics, or "disturbed flows," are linked to arterial diseases and consequently that minimization of "disturbed flow" indicators leads to geometric bifurcation designs that lower postoperative complication rates. Considering transient 3-D laminar blood flow in partially occluded, in-plane, rigid-wall carotid artery bifurcations, the results presented include time-averaged indicators of "disturbed flow", such as the wall shear stress, spatial wall shear stress gradient, and wall shear stress angle deviation. In addition, trajectories and deposition patterns of critical blood particles (i.e., monocytes) are shown and evaluated. Within given physiological constraints, the vessel geometry was then changed in order to reduce the magnitudes of key indicators associated with thrombosis (i.e., blood clot formation) or restenosis (e.g., renewed atherosclerosis and/or hyperplasia). The quantitative results and knowledge base generated will be crucial for future clinical trials.}, number={1-2}, journal={CRITICAL REVIEWS IN BIOMEDICAL ENGINEERING}, author={Hyun, S and Kleinstreuer, C and Archie, JP}, year={2000}, pages={53–59} }
 @article{hyun_kleinstreuer_archie_2000, title={Hemodynamics analyses of arterial expansions with implications to thrombosis and restenosis}, volume={22}, ISSN={["1350-4533"]}, DOI={10.1016/S1350-4533(00)00006-0}, abstractNote={It is assumed that critical hemodynamic factors play an important role in the onset, localization and degree of post-operative complications, for example, thrombosis and restenosis. Of special interest are sudden expansion flows, which may occur in straight artery segments such as the common carotid after endarterectomy or end-to-end anastomoses. Sudden expansion geometries are possible origins of early post-operative emboli and significant myointimal hyperplasia resulting in early or late complications. Transient laminar axisymmetric and fully three-dimensional blood flows were simulated employing a validated finite volume code in conjunction with a Runge–Kutta particle tracking technique. Disturbed flow indicators, which may predict the onset of thrombosis and/or restenosis, were identified and employed to evaluate 90°-step and smooth expansion geometries. Smooth expansion geometries have weaker disturbed flow features than step expansion geometries. Specifically, the regions near the expansion wall and the reattachment point are susceptible to both atherosclerotic lesion and thrombi formations as indicated by non-uniform hemodynamic indicators such as near-zero wall shear stress and elevated wall shear stress gradients as well as blood particle accumulation and deposition. A new parameter, the wall shear stress angle deviation (WSSAD) has been introduced, which indicates areas of abnormal endothelial cell morphology and particle wall deposition. In turn, regions of low wall shear stress and high wall shear stress gradients are recognized as susceptible sites for arterial diseases. Thus, it is interesting to note that high WSSAD surface areas cover low wall shear stress, high wall shear stress gradient locations as well as high wall particle deposition. A gradual change in step expansion geometry provides better results in terms of WSSAD values and hence potentially reducing atherosclerosis as well as thrombi formation.}, number={1}, journal={MEDICAL ENGINEERING & PHYSICS}, author={Hyun, S and Kleinstreuer, C and Archie, JP}, year={2000}, month={Jan}, pages={13–27} }
 @article{lei_archie_kleinstreuer_1997, title={Computational design of a bypass graft that minimizes wall shear stress gradients in the region of the distal anastomosis}, volume={25}, ISSN={["0741-5214"]}, DOI={10.1016/S0741-5214(97)70289-1}, abstractNote={Recent experimental and theoretic studies show that large wall shear stress gradients characterize disturbed flow patterns associated with the location of myointimal hyperplasia, atheroma, or both. Graft-to-artery anastomoses that minimize wall shear stress gradients may reduce the degree of myointimal development and the propensity for thrombosis. This study analyzes the distribution of distal anastomotic wall shear stress gradients for conventional geometries and for the optimized geometry assuming idealized merging of the graft with the artery.A validated computational fluid dynamics program was used to solve the transient three-dimensional partial differential equations and auxiliary equations that describe laminar incompressible blood flow. Time-averaged wall shear stresses and wall shear stress gradients were calculated for three distal graft-artery anastomoses: a standard end-to-side, a Taylor patch, and an optimized geometry. The latter was obtained iteratively by minimizing the local wall shear stress gradients and was analyzed under resting and exercise inflow waveforms.Both the standard and Taylor patch anastomoses have relatively high wall shear stress gradients in the regions of the toe and heel. For all flow inputs studied nonuniform hemodynamics in the optimized graft design are largely eliminated, and the time-averaged wall shear stress gradients are greatly reduced throughout the anastomotic zone. At resting flow the Taylor patch produces slightly lower wall shear stress gradients in the anastomotic region than the standard end-to-side anastomosis. The optimized design reduces wall shear stress gradients to almost one half of that of the standard and Taylor patch geometries. At exercise flow wall shear stress gradients almost triple in the standard anastomosis and increase approximately 30% in the Taylor patch. In contrast, the geometrically optimized design is basically independent of the type of flow input waveform in terms of time-averaged wall shear stress gradients and disturbed flow patterns.This study demonstrates that it is possible to design a terminal graft geometry for an end-to-side anastomosis that significantly reduces wall shear stress gradients. If the wall shear stress gradient is confirmed to be a major hemodynamic determinant of intimal hyperplasia and restenosis, these results may point to the design of optimal bypass graft geometries.}, number={4}, journal={JOURNAL OF VASCULAR SURGERY}, author={Lei, M and Archie, JP and Kleinstreuer, C}, year={1997}, month={Apr}, pages={637–646} }
 @article{lei_kleinstreuer_archie_1997, title={Hemodynamic simulations and computer aided designs of graft-artery junctions}, volume={119}, ISSN={["0148-0731"]}, DOI={10.1115/1.2796099}, abstractNote={Severe occlusion of graft–artery junctions due to restenosis, e.g., excessive tissue overgrowth and renewed plaque formation, may occur within a few months or years after bypass surgery. Our hypothesis is that nonuniform hemodynamics, represented by large sustained wall shear stress gradients, trigger abnormal biological processes leading to rapid restenosis and hence early graft failure. In turn, this problem may be significantly mitigated by designing graft-artery bypass configurations for which the wall shear stress gradient (WSSG) is approximately zero and hence nearly uniform hemodynamics are achieved. Focusing on the distal end of several femoral artery bypass junctions, a validated finite volume code has been used to compute the transient three-dimensional velocity vector fields and its first and second surface derivatives in order to test the idea. Specifically, it is shown that the Taylor patch, which generates higher patency rates than standard end-to-side anastomoses, exhibits lower WSSG levels than standard configurations, and that further geometric design improvements reduce the WSSG in magnitude and local extent even more.}, number={3}, journal={JOURNAL OF BIOMECHANICAL ENGINEERING-TRANSACTIONS OF THE ASME}, author={Lei, M and Kleinstreuer, C and Archie, JP}, year={1997}, month={Aug}, pages={343–348} }