Effect of exercise on patient specific abdominal aortic aneurysm flow topology and mixing

Arzani, Amirhossein; Les, Andrea S.; Dalman, Ronald L.; Shadden, Shawn C.

doi:10.1002/cnm.2601

Cited by 25 publications

(21 citation statements)

References 37 publications

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“…However, this quasi-steady behavior can break down if the Reynolds and Womersley numbers are sufficiently increased. For example, exercise in AAA patients creates a more complex flow field [2], with higher WSS values [33]. A preliminary investigation of our methods on AAA exercise data showed that the WSS LCS can slightly fluctuate around the stable/unstable manifolds of TAWSS and demonstrate some time dependence behavior (results not shown).…”

Section: P 10mentioning

confidence: 90%

Wall shear stress exposure time: a Lagrangian measure of near-wall stagnation and concentration in cardiovascular flows

Arzani

Gambaruto

Chen

et al. 2016

Biomech Model Mechanobiol

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General rightsThis document is made available in accordance with publisher policies. Please cite only the published version using the reference above. Full terms of use are available: http://www.bristol.ac.uk/pure/about/ebr-terms suitable in regions of complex hemodynamics that are traditionally difficult to quantify, yet encountered in many disease scenarios. Keywords: advection-diffusion; blood flow; hemodynamics; near-wall transport; residence time; shear stress; p. 2 IntroductionBiomechanical interactions between blood flow and the vessel wall are central to the initiation and progression of most cardiovascular diseases. Indeed, the majority of computational and experimental investigations into blood flow seek to understand how local flow mechanics relates to disease progression in or on the vessel wall. Blood flow conditions in diseased vessels are usually spatially and temporally complex and are challenging to characterize [51,50], even without reference to the coupled biochemical or biophysical processes driving disease progression. Nonetheless, the role of blood flow mechanics in the "near-wall" region is of utmost importance since this is where such couplings are most profound. In the near-wall region, blood flow serves to impart mechanical stresses on the vessel wall, as well as regulate the local transport of reactive material between the tissue and fluid domains. It is this latter mechanism that motivates the work presented herein.A compelling scenario involving the interaction between blood flow and the vessel wall is atherosclerosis, which is a leading cause of death worldwide. Atherosclerosis occurs mainly in locations of disturbed blood flow patterns [9,47]. The local transport of several substances near and at the vessel wall are known to influence atherosclerosis progression [56]. For example, previous studies have looked into transport of low density lipoproteins (LDL) [17,20,30,14], high density lipoproteins (HDL) [40,24], oxygen [16,27], nitric oxide (NO) [45,35], monocytes [12,14], and adenine triphosphate ATP and adenine diphosphate ADP [13,15,8] as important mass transport processes involved in atherosclerosis.Intravascular thrombosis is another compelling pathology associated with most cardiovascular diseases where near-wall transport becomes important [7,25]. The trajectories of individual platelets and the accumulation and residence time of chemical solutes including ADP, thrombin, and various blood factors control clot formation. These solutes, and especially in activated form, are generated at the vessel wall or from bound platelets. Complex hemodynamics and flow stagnation are often associated with prothrombotic conditions. For example, intraluminal thrombus in abdominal aortic aneurysm (AAA) [57,54] complicates disease progression, and is thought to be strongly coupled to flow stagnation and recirculation. The chaotic flow field in AAAs [3] Near-wall transport can either be (i) explicitly modeled for a specific transport problem, or (ii) inferred from appropriate hemodynamics meas...

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Section: P 10mentioning

confidence: 90%

Wall shear stress exposure time: a Lagrangian measure of near-wall stagnation and concentration in cardiovascular flows

Arzani

Gambaruto

Chen

et al. 2016

Biomech Model Mechanobiol

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“…While the in vivo profile at the supraceliac aorta likely deviates from a Womerseley profile, imposing the profile at the supraceliac level ensures sufficient length for the flow to develop so that flow features at the infrarenal segment are not sensitive to the profile at the supraceliac level (4,39).…”

Section: Methodsmentioning

confidence: 99%

“…Degradation of the aortic wall, inflammation with immune responses, and biochemical wall stress are mechanisms that promote AAA initiation, influenced by molecular genetics (1). After the irreversible process of aneurysm formation, the dilated vessel creates an environment with complex blood flow and wall shear stress distribution (4,5,9,14,22,37,38), which is thought to perpetuate aneurysm progression.The presence of intraluminal thrombus (ILT) complicates AAA growth. ILT is fibrin structure compound of platelets, blood cells, blood proteins, and cellular debris (20).…”

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confidence: 99%

A longitudinal comparison of hemodynamics and intraluminal thrombus deposition in abdominal aortic aneurysms

Arzani

Suh

Dalman

et al. 2014

American Journal of Physiology-Heart and Circulatory Physiology

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(ILT), which complicates AAA progression and risk of rupture. Patient-specific computational fluid dynamics modeling of 10 small human AAA was performed to investigate relations between hemodynamics and ILT progression. The patients were imaged using magnetic resonance twice in a 2-to 3-yr interval. Wall content data were obtained by a planar T1-weighted fast spin echo black-blood scan, which enabled quantification of thrombus thickness at midaneurysm location during baseline and followup. Computational simulations with patient-specific geometry and boundary conditions were performed to quantify the hemodynamic parameters of time-averaged wall shear stress (TAWSS), oscillatory shear index (OSI), and mean exposure time at baseline. Spatially resolved quantifications of the change in ILT thickness were compared with the different hemodynamic parameters. Regions of low OSI had the strongest correlation with ILT growth and demonstrated a statistically significant correlation coefficient. Prominent regions of high OSI (Ͼ0.4) and low TAWSS (Ͻ1 dyn/cm 2 ) did not appear to coincide with locations of thrombus deposition. computational fluid dynamics; hemodynamics; oscillatory shear index; thrombosis; wall shear stress ABDOMINAL AORTIC ANEURYSM (AAA) is a permanent dilation (50% greater than the normal arterial wall diameter) of the abdominal aorta. The disease is progressive and fatal if untreated. Between 11,000 and 17,000 patients die annually in the United States (18a) from AAA rupture following progressive, often asymptomatic, enlargement, and only invasive treatments have proven effective at preventing rupture and premature death (13). Male gender, age, smoking, genetic factors, hypertension, and high cholesterol are among known risk factors (10), and diabetes is a negative risk factor (47). Degradation of the aortic wall, inflammation with immune responses, and biochemical wall stress are mechanisms that promote AAA initiation, influenced by molecular genetics (1). After the irreversible process of aneurysm formation, the dilated vessel creates an environment with complex blood flow and wall shear stress distribution (4,5,9,14,22,37,38), which is thought to perpetuate aneurysm progression.The presence of intraluminal thrombus (ILT) complicates AAA growth. ILT is fibrin structure compound of platelets, blood cells, blood proteins, and cellular debris (20). ILT is more frequent in larger AAA since most patients develop thrombus as the aneurysm progresses. It has been proposed that platelets activate in regions of high shear and are subsequently advected towards the aneurysm wall where they accumulate in regions of low shear and form thrombus (8), with a possible role played by the vortical structures formed inside the aneurysm (9). It has also been shown that the flow field inside AAA may promote ILT formation by increasing residence time and trapping blood particles (7,37,38).The effect of ILT on AAA progression and rupture remains controversial (48). ILT may deprive the aneurysm wall of oxygen, which may exacerba...

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“…We have performed preliminary study on the effect of simulated exercise flow conditions (increased Reynolds and Womersley numbers, as modeled in Arzani et al (2014a)) on WSS LCS, and observed that the quasi-steady behavior of near wall transport can break down due to the higher WSS magnitudes. In addition, pulsatile blood flow may have some cycle to cycle variations due to transient effects from the fluid mechanics or physiology.…”

Section: Discussionmentioning

confidence: 99%

Lagrangian wall shear stress structures and near-wall transport in high-Schmidt-number aneurysmal flows

et al. 2016

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The wall shear stress (WSS) vector field provides a signature for near wall convective transport, and can be scaled to obtain a first order approximation of the near wall fluid velocity. The near wall flow field governs mass transfer problems in convection dominated open flows with high Schmidt number, in which case a flux at the wall will lead to a thin concentration boundary layer. Such near wall transport is of particular interest in cardiovascular flows whereby hemodynamics can initiate and progress biological events at the vessel wall. In this study we consider mass transfer processes in pulsatile blood flow of abdominal aortic aneurysms resulting from complex WSS patterns. Specifically, the Lagrangian surface transport of a species released at the vessel wall was advected in forward and backward time based on the near wall velocity field. Exposure time and residence time measures were defined to quantify accumulation of trajectories, as well as the time required to escape the near wall domain. The effect of diffusion and normal velocity was investigated. The trajectories induced by the WSS vector field were observed to form attracting and repelling coherent structures that delineated species distribution inside the boundary layer consistent with exposure and residence time measures. The results indicate that Lagrangian wall shear stress structures can provide a template for near wall transport.

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Effect of exercise on patient specific abdominal aortic aneurysm flow topology and mixing

Cited by 25 publications

References 37 publications

Wall shear stress exposure time: a Lagrangian measure of near-wall stagnation and concentration in cardiovascular flows

Wall shear stress exposure time: a Lagrangian measure of near-wall stagnation and concentration in cardiovascular flows

A longitudinal comparison of hemodynamics and intraluminal thrombus deposition in abdominal aortic aneurysms

Lagrangian wall shear stress structures and near-wall transport in high-Schmidt-number aneurysmal flows

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