Steady flow in a model of the human carotid bifurcation. Part I—Flow visualization

Bharadvaj, Bala; Mabon, Robert F.; Giddens, Don P.

doi:10.1016/0021-9290(82)90057-4

Cited by 277 publications

(161 citation statements)

References 19 publications

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“…However, regions that have steady blood flow are usually atheroprotected (7,16). Endothelial dysfunction in conditions with reverse flow may be explained by the significantly increased production of O 2 Ϫ in the reverse flow.…”

Section: Discussionmentioning

confidence: 99%

NADPH oxidase has a directional response to shear stress

Godbole¹,

Lu²,

Guo³

et al. 2009

American Journal of Physiology-Heart and Circulatory Physiology

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Godbole AS, Lu X, Guo X, Kassab GS. NADPH oxidase has a directional response to shear stress. Am J Physiol Heart Circ Physiol 296: H152-H158, 2009. First published November 14, 2008 doi:10.1152/ajpheart.01251.2007.-Vessel regions with predilection to atherosclerosis have negative wall shear stress due to flow reversal. The flow reversal causes the production of superoxides (O 2 Ϫ ), which scavenge nitric oxide (NO), leading to a decrease in NO bioavailability and endothelial dysfunction. Here, we implicate NADPH oxidase as the primary source of O 2 Ϫ during full flow reversal. Nitrite production and the degree of vasodilation were measured in 46 porcine common femoral arteries in an ex vivo system. Nitrite production and vasodilation were determined before and after the inhibition of NADPH oxidase, xanthine oxidase, or mitochondrial oxidase. NADPH oxidase inhibition with gp91ds-tat or apocynin restored nitrite production and vasodilation during reverse flow. Xanthine oxidase inhibition increased nitrite production at the highest flow rate, whereas mitochondrial oxidase inhibition had no effect. These findings suggest that the NADPH oxidase system can respond to directional changes of flow and is activated to generate O 2 Ϫ during reverse flow in a dose-dependent fashion. These findings have important clinical implications for oxidative balance and NO bioavailability in regions of flow reversal in a normal and compromised cardiovascular system. superoxide; nitric oxide; oxidative balance; reduced nicotinamide adenine dinucleotide phosphate NITRIC OXIDE (NO) is released by endothelial cells to regulate blood vessel diameter acutely as well as to maintain long-term homeostatic conditions of the vessel wall (4,30). NO is produced in the endothelium from L-arginine by the enzyme endothelial NO synthase (eNOS) (4, 41) and is released in response to endothelial shear stress and other stimuli such as acetylcholine (4). Wall shear stress (WSS) has also been found to regulate the activity and expression of eNOS (34,40).Oscillatory and reverse WSS have negative effects on the endothelium due to superoxide (O 2 Ϫ ) production (14, 27, 28, 36, 52). It has been found that reverse flow in blood vessels causes reduced NO due to increased O 2 Ϫ production (36). Since NO is atheroprotective, regions of oscillatory and reverse WSS are more prone to atherosclerosis. Regions near branch points and curved vessels produce near-wall reverse flow (15,16).O 2 Ϫ can quickly inactivate NO, causing reduced NO bioavailability and endothelial dysfunction (9, 33). This endothelial dysfunction is implicated in atherosclerosis, hypertension, and heart failure (9,13,14,18,21). Reduced NO in the vessel wall impairs endothelium-dependent vasodilation, decreases inhibition of platelet and leukocyte adhesion, and is linked to the development of intimal hyperplasia (4, 21, 51). Our group has previously shown that NO production is reduced during reverse flow and that the addition of Tempol (an O 2 Ϫ scavenger) restored NO production in reverse flow to...

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Section: Discussionmentioning

confidence: 99%

NADPH oxidase has a directional response to shear stress

Godbole¹,

Lu²,

Guo³

et al. 2009

American Journal of Physiology-Heart and Circulatory Physiology

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“…3 The human carotid pulse was simulated by a half-sine wave with DC offset to model the acceleration and deceleration of systole, followed by a relatively steady period of positive diastolic flow ( figure 1 A). A servocontrolled shaker valve was connected in series with a constant pressure head to generate the pulsatile flow.…”

Section: Methodsmentioning

confidence: 99%

“…An additional complication is the fact that hydrogen bubbles do not precisely follow the trajectories of fluid elements due to buoyancy, although this effect is small in these studies. 3 Figures 2-5 (see Results section) were obtained under conditions of continuous bubble generation and, consequently, the motion visualized represents streaklines of the flow. For figures 6 and 7, the bubbles were generated for one cycle, and then the wire current was abruptly stopped before the photographs were taken.…”

Section: Methodsmentioning

confidence: 99%

“…2 Recent investigators have described an average geometry of the human carotid bifurcation based on bipianar angiograms and cadaver specimens. 3 Steady flows at physiological Reynolds numbers and flow division ratios have been visualized 35 and quantified. 4 These results indicated circumferential secondary helices in the internal carotid branch, very low wall shear stresses at the outer wall of the sinus, and relatively large shear stresses at the apex and distal end of the sinus as the flow enters the internal carotid artery.…”

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Pulsatile flow in a model carotid bifurcation.

Ku¹,

Giddens²

1983

Arteriosclerosis

201

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T he flow at the carotid artery bifurcation may have significant bearing on the development and management of atherosclerosis in this major blood vessel. For over a century, hypotheses have linked flow disturbances at this and other arterial branches with the formation of atheromas. Furthermore, advances in noninvasive ultrasound studies of blood velocity in the carotid arteries have pointed to the need for a more rigorous understanding of normal physiologic flow patterns at this branch. Fluid flow patterns at branches are highly dependent on geometry, Reynolds number, and flow division ratios. In the case of human physiology, the flow is additionally pulsatile, introducing a time-dependent behavior. Second order effects which influence the flow, but to a much lesser degree, are the compliance of the arterial wall 1 and the non-Newtonian viscosity of blood. 2 Recent investigators have described an average geometry of the human carotid bifurcation based on bipianar angiograms and cadaver specimens. quantified. 4 These results indicated circumferential secondary helices in the internal carotid branch, very low wall shear stresses at the outer wall of the sinus, and relatively large shear stresses at the apex and distal end of the sinus as the flow enters the internal carotid artery. No turbulence was observed in those studies. The secondary flow appeared to be influenced most strongly by a flow division between the daughter branches and, to a lesser degree, by the upstream Reynolds number.This paper presents the results of visualization of pulsatile flow patterns in a model of the carotid bifurcation and compares our observations to the results obtained with steady flow experiments. MethodsThe model used in this study was constructed of blown glass after determining an average geometry from 57 bipianar angiograms of 22 adult subjects ranging from age 34 to 77 years. 3 The human carotid pulse was simulated by a half-sine wave with DC offset to model the acceleration and deceleration of systole, followed by a relatively steady period of positive diastolic flow ( figure 1 A). A servocontrolled shaker valve was connected in series with a constant pressure head to generate the pulsatile flow.

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“…The problem is defined by two variables: the eccentricity E and the Reynolds number Re. Using the diameter of the common carotid artery, Bharadvaj, Mabon, and Giddens 13 showed that a representative, time-averaged, Reynolds number for this blood vessel isRe = 380. It was also noted, however, that because blood flow is pulsatile, the peak Reynolds number can be as high as 1200.…”

Section: A Problem Setupmentioning

confidence: 99%

Breaking axi-symmetry in stenotic flow lowers the critical transition Reynolds number

2015

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Flow through a sinuous stenosis with varying degrees of non-axisymmetric shape variations and at Reynolds number ranging from 250 to 750 is investigated using direct numerical simulation (DNS) and global linear stability analysis. At low Reynolds numbers (Re < 390), the flow is always steady and symmetric for an axisymmetric geometry. Two steady state solutions are obtained when the Reynolds number is increased: a symmetric steady state and an eccentric, non-axisymmetric steady state. Either one can be obtained in the DNS depending on the initial condition. A linear global stability analysis around the symmetric and non-axisymmetric steady state reveals that both flows are linearly stable for the same Reynolds number, showing that the first bifurcation from symmetry to antisymmetry is subcritical. When the Reynolds number is increased further, the symmetric state becomes linearly unstable to an eigenmode, which drives the flow towards the non-axisymmetric state. The symmetric state remains steady up to Re = 713, while the non-axisymmetric state displays regimes of periodic oscillations for Re ≥ 417 and intermittency for Re 525. Further, an offset of the stenosis throat is introduced through the eccentricity parameter E. When eccentricity is increased from zero to only 0.3% of the pipe diameter, the bifurcation Reynolds number decreases by more than 50%, showing that it is highly sensitive to non-axisymmetric shape variations. Based on the resulting bifurcation map and its dependency on E, we resolve the discrepancies between previous experimental and computational studies. We also present excellent agreement between our numerical results and previous experimental results. C 2015 AIP Publishing LLC.

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Steady flow in a model of the human carotid bifurcation. Part I—Flow visualization

Cited by 277 publications

References 19 publications

NADPH oxidase has a directional response to shear stress

NADPH oxidase has a directional response to shear stress

Pulsatile flow in a model carotid bifurcation.

Breaking axi-symmetry in stenotic flow lowers the critical transition Reynolds number

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