Elsevier

Journal of Biomechanics

Volume 49, Issue 13, 6 September 2016, Pages 2960-2967
Journal of Biomechanics

Flow characteristics around proximal and distal stenoses in a series of tandem stenosed vessels

https://doi.org/10.1016/j.jbiomech.2016.07.014Get rights and content

Abstract

The flow characteristics around the proximal and distal stenoses in tandem vessel models are experimentally investigated with varying flow rates (Q=0.25, 0.5, 1.0 L/min), interspacing distances (L=3, 6, 10 of diameter D) and severities (S=50%, 75% reduction in diameter). When the interspacing L is larger than 10 D, no fluid-dynamic interaction is observed. The flow between the proximal and distal stenoses becomes stabilized (turbulence intensity of <3%) as the interspacing distance decreases. When the severity S is 75%, the transition from laminar to turbulent flow occurs at a flow rate higher than 0.5 L/min, although the interspacing distance L is 3 D. Formation of recirculation flow is restricted by the presence of distal stenosis as the interspacing distance decreases. In this case, the flow between the stenoses is focused on the central region. The center-line velocity at the neck of the distal stenosis is approximately 10–15% higher than that of the proximal stenosis with equal severity of S=50%. When the inlet flow is center-focused, the lengths of the recirculation and the jet core behind the distal stenosis increase with decrease in interspacing distance L. When the inlet flow is turbulent, the transition from laminar to turbulent flow occurs early as the interspacing distance L is reduced. When the upstream proximal stenosis exhibits increased severity, the pressure drop is measured to be 20% compared with that when the severity of the downstream distal stenosis is increased at the flow rate of Q=1.0 L/min.

Introduction

Atherosclerosis is well known as the key cause of heart attacks, strokes, and peripheral vascular diseases. Previous studies have reported that the hemodynamic characteristics in arterial blood vessels are closely associated with the cause, progress, and prognosis of atherosclerosis (Blankenhorn and Hodis, 1993; Williams and Tabas, 1995). The morphological and functional expression levels of endothelial cells in blood vessels are regulated by wall shear stress (Hahn and Schwartz, 2009), especially to low and oscillating shear stresses (Caro et al., 1971; Ku et al., 1985; Myers et al., 2001).

Bifurcation or stenosis geometry can cause localized recirculation or flow disturbances in blood vessels. In particular, the flow is disturbed and separated from the crest of the stenosis when blood passes through a stenosed vessel. Additionally, vortex shedding and transition from laminar to turbulent flow occur in the post-stenosis region, depending on the flow conditions (Bluestein et al., 1999; Bluestein et al., 1997). The wall shear stress in the post-stenosis region yields low and oscillating values when localized recirculation and flow transition occur. Hence even arteries with mild stenosis may demonstrate transitional flow or turbulence, as previously reported by Clark (1976) and Ahmed and Giddens (1983).

Considering the above aspects, stenosis in arterial vessels is one of the main parameters for the development of the secondary stenosis distal to the primary one (Rathish Kumar et al., 2002). These tandem stenoses are observed in arteries with diffused atherosclerosis or arterial dysplasia(Bertolotti et al., 2006; Lee, 1994). The stenosis in carotid bifurcation and ipsilateral extracranial stenosis in tandem with intracranial atherosclerotic disease occupies approximately 20% and 50% of the symptomatic cerebral ischemia, respectively (NASCET, 1991). However, the main contributing stenosis for such symptoms are not clearly identified, because the related hemodynamic information about tandem stenosis is insufficient yet. In addition, tandem stenosis formed extracranially and intracranially in the carotid artery is difficult to separately access for clinical treatments (Li et al., 2010). Thus, tandem stenting of both stenoses (Tsutsumi et al., 2003) or carotid endarterectomy and percutaneous transluminal angioplasty using a Y-shaped shunt tube have been adopted to treat multiple stenoses simultaneously (Terada et al., 1998). However, it is burden for both surgeons and the patients, when one of the stenoses is located intracranially. Therefore, detailed understanding about the hemodynamic features of tandem stenosis is crucial for proper clinical diagnosis or treatment of circulatory vascular diseases.

The flows behind a single stenosis are characterized by the inlet flow Reynolds number (Re=ρUD/μ=ρQD/μA) where, U, and A indicate the density, inlet velocity, and cross-sectional area of the stenosis model, and critical Reynolds number Recr of the given experimental conditions. When Re<Recr, the flow is laminar and the length of the recirculation zone is increased as Re increases. When Re>Recr, the laminar flow is transited to turbulent flow, and the length of the recirculation zone decreases as Re increases. Recr is around 400 for flows behind a stenosis with 50% severity (Ha and Lee, 2014; Vétel et al., 2008). Similar criteria is expanded to the tandem stenosis.

Lee (1994) numerically analyzed the effect of severity on the recirculation, pressure drop, wall shear stress, and vorticity distribution for a steady laminar flow. Later on, Lee et al. (2003) reported similar works on pulsatile and turbulent flows. Pulsatile laminar flows passing through a tandem stenosed vessel were numerically investigated by Rathish Kumar et al. (2002). Karayannacos et al. (1977) reported that the pressure drop caused by multiple stenoses was the sum of the pressure drops for individual stenoses with minor dependence upon the interspacing distance between stenoses. Seeley and Young (1976) demonstrated that the interspacing distance (L) plays a significant role in pressure drops. Li et al. (2010) simulated the hemodynamic effect of tandem carotid artery stenosis to facilitate clinical decisions for carotid endarterectomy. Research of Bertolotti et al. (2006) evaluated the pressure drop and peak systolic velocity ratio through echo-Doppler functional diagnosis with comparison of steady-flow simulation results with steady and pulsatile flow experiments. Although various numerical simulations have studied the hemodynamic effects of tandem stenosis on the pressure drop or wall shear stress, detailed information on the flow characteristics in tandem stenosed vessels under turbulent flow conditions is still lacking.

In the current study, the hemodynamic characteristics of flows around the proximal and distal stenoses in tandem stenosis models with varying interspacing distance L, severity S, and flow rate Q are quantitatively investigated using particle image velocimetry (PIV) technique under in vitro condition. The centerline velocity, laminar-to-turbulent flow transition, vorticity contour, and recirculation zone are compared to identify the effects of the flow behind the proximal stenosis on the flow around the distal stenosis and vice versa.

Section snippets

Methods

The blood-mimicking working fluid is prepared by mixing 1% distilled water, 20% glycerol, and 79% saturated aqueous sodium iodine (NaI) by volume (Deutsch et al., 2006). The kinematic viscosity measured using a viscometer (LVDV2+Pro, Brookfield, USA) is approximately 2.8±0.005 cSt (cSt), while the density of the fluid ρf is 1.06 g/m3. NaI is added to the working fluid to obtain a refractive index of n=1.491±0.001, corresponding to the refractive index of the acrylic stenosis model. The refractive

Effect of interspacing distance

The mean velocity fields of the flow behind the proximal stenosis for L=3 and 10 D at Q=0.25 L/min are shown in Fig. 2a for P50_D50. A recirculation flow formed in the post-proximal stenosis region is extended up to the X/D~8 from the crest (X/D=0) of the proximal stenosis when L=10 D. The size of the recirculation zone is suppressed as the L=3 D, and flow separation occurs at the neck of the distal stenosis.

The length of the recirculation zone is gradually decreased as the flow rate increases

Discussion

The flow rates selected in current study are Q=0.25, 0.5, 1 L/min, corresponding to the minimum, average, and maximum flow rates in the common carotid artery of normal humans (Holdsworth et al., 1999). Corresponding Reynolds numbers of Re=187, 375, 750 represent the laminar, transitional, and turbulent flow behind a stenosis with 50% severity, respectively. Recr decreases as the severity of the stenosis increases, indicating the earlier occurrence of turbulence behind the severe stenosis at a

Conclusions

In this study, the effects of three different flow rates (laminar, transitional, and turbulent), three interspacing distances (3, 6, and 10 D) and two severities (50% and 75%) on the flow characteristics in tandem stenosis are experimentally investigated.

As the interspacing distance decreases, flows in the middle section between the proximal and distal stenoses are stabilized until the Reynolds number Re reaches the upper limit. The transition from laminar to turbulent flow is prolonged when Re>

Conflict of interest

None declared.

Funding

This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (No. 2008-0061991).

Acknowledgment

We thank for the support of the NRF of Korea through the Creative Research Initiatives program.

References (27)

  • D. Bluestein et al.

    Vortex shedding in steady flow through a model of an arterial stenosis and its relevance to mural platelet deposition

    Ann. Biomed. Eng.

    (1999)
  • D. Bluestein et al.

    Fluid mechanics of arterial stenosis: relationship to the development of mural thrombus

    Ann. Biomed. Eng.

    (1997)
  • C. Caro et al.

    Atheroma and arterial wall shear observation, correlation and proposal of a shear dependent mass transfer mechanism for atherogenesis

    Proc. R. Soc. Lond. B: Biol. Sci.

    (1971)
  • Cited by (10)

    • Insight into distribution of wall pressure, wall shear stress, and oscillatory shear index: Pulsatile flow of blood subject to Lorentz force

      2022, Forces in Mechanics
      Citation Excerpt :

      Stenotic lesions in coronary arteries reduce the transportation of blood to the heart muscles for efficient functioning of heart. This eventually results in cardiac arrest [1]. Sometime a stenotic lesion may rupture and form blood clots or thrombus.

    • Experimental and numerical investigation of pulsed flows in asevere aortic stenosed model

      2021, Medical Engineering and Physics
      Citation Excerpt :

      The existence of low wall shear stress regions between the proximal and distal stenosis can raise atherosclerotic growth. Huh et al. [7] reported similar numerical simulations results in tandem stenosed vessels, with a maximum wall shear stress of 9 Pa obtained at the stenosis throat. The wall shear stress is always larger for the fastest case of heartbeat (90bpm) except for phases t/T=1/6 and t/T=2/6.

    View all citing articles on Scopus
    View full text