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Fluid-dynamic optimal design of helical vascular graft for stenotic disturbed flow.

Ha H, Hwang D, Choi WR, Baek J, Lee SJ - PLoS ONE (2014)

Bottom Line: Results showed that the swirling intensity and helicity of the swirling flow have a linear relation with a modified Germano number (Gn*) of the helical pipe.In addition, the swirling flow generated a beneficial flow structure at the stenosis by reducing the size of the recirculation flow under steady and pulsatile flow conditions.Therefore, the beneficial effects of a helical graft on the flow field can be estimated by using the magnitude of Gn*.

View Article: PubMed Central - PubMed

Affiliation: Department of Mechanical Engineering, Pohang University of Science and Technology (POSTECH), Pohang, Gyeongbuk, Republic of Korea.

ABSTRACT
Although a helical configuration of a prosthetic vascular graft appears to be clinically beneficial in suppressing thrombosis and intimal hyperplasia, an optimization of a helical design has yet to be achieved because of the lack of a detailed understanding on hemodynamic features in helical grafts and their fluid dynamic influences. In the present study, the swirling flow in a helical graft was hypothesized to have beneficial influences on a disturbed flow structure such as stenotic flow. The characteristics of swirling flows generated by helical tubes with various helical pitches and curvatures were investigated to prove the hypothesis. The fluid dynamic influences of these helical tubes on stenotic flow were quantitatively analysed by using a particle image velocimetry technique. Results showed that the swirling intensity and helicity of the swirling flow have a linear relation with a modified Germano number (Gn*) of the helical pipe. In addition, the swirling flow generated a beneficial flow structure at the stenosis by reducing the size of the recirculation flow under steady and pulsatile flow conditions. Therefore, the beneficial effects of a helical graft on the flow field can be estimated by using the magnitude of Gn*. Finally, an optimized helical design with a maximum Gn* was suggested for the future design of a vascular graft.

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The effect of pulsatile swirling flow on the flow reattachment (L/D) and OSI at the post-stenosis.(a) Variations of flow reattachment (L/D) obtained from phase-averaged velocity fields, (b) OSI distribution at the post-stenosis. The Poiseuille flow (upper) and swirling flow (lower) are generated by the straight and helical tubes (Rc/R0 = 0.6, H/R0 = 4).
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pone-0111047-g015: The effect of pulsatile swirling flow on the flow reattachment (L/D) and OSI at the post-stenosis.(a) Variations of flow reattachment (L/D) obtained from phase-averaged velocity fields, (b) OSI distribution at the post-stenosis. The Poiseuille flow (upper) and swirling flow (lower) are generated by the straight and helical tubes (Rc/R0 = 0.6, H/R0 = 4).

Mentions: At the early systole phase (t/T = 0.15), the jet flow starts to develop at the post-stenosis region. As the flow rate increases, the recirculation regions develop at t/T = 0.25. At t/T = 0.39, the length of the jet reaches the maximum at the peak flow rate. At this point, the swirling flow condition has a shorter jet flow length and a smaller recirculation flow area compared with the Poiseuille flow. At the diastole phase (0.39≤ t/T≤1.0), the recirculation flow at the swirling flow condition rapidly decreases along with the flow rate. On the contrary, the recirculation flow structure is maintained at t/T = 0.90 when the Poiseuille flow serves as an inlet to the stenosis. Figure 15a quantitatively presents the variations of phase-averaged flow reattachment length (L/D). The result shows that both of the maximum and mean L/D are reduced up to 1.0D by the introduction of the swirling flow. This clearly shows that the swirling flow inhibits the development of the recirculation flow structure at the post-stenosis under the physiological pulsatile flow condition. Since the retrograde flow in the recirculation area induces relatively high WSS oscillation during the pulsating cycle, the size of the recirculation flow is directly related to the area of high OSI distribution at the post-stenosis. Figure 15b presents the effect of pulsatile swirling flow on the OSI distribution at the post-steonsis. The results shows that the introduction of the swirling flow confines the high OSI region to X/D<2.5 while the Poiseuille flow induces causes the high OSI region up to X/D<4.


Fluid-dynamic optimal design of helical vascular graft for stenotic disturbed flow.

Ha H, Hwang D, Choi WR, Baek J, Lee SJ - PLoS ONE (2014)

The effect of pulsatile swirling flow on the flow reattachment (L/D) and OSI at the post-stenosis.(a) Variations of flow reattachment (L/D) obtained from phase-averaged velocity fields, (b) OSI distribution at the post-stenosis. The Poiseuille flow (upper) and swirling flow (lower) are generated by the straight and helical tubes (Rc/R0 = 0.6, H/R0 = 4).
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4215892&req=5

pone-0111047-g015: The effect of pulsatile swirling flow on the flow reattachment (L/D) and OSI at the post-stenosis.(a) Variations of flow reattachment (L/D) obtained from phase-averaged velocity fields, (b) OSI distribution at the post-stenosis. The Poiseuille flow (upper) and swirling flow (lower) are generated by the straight and helical tubes (Rc/R0 = 0.6, H/R0 = 4).
Mentions: At the early systole phase (t/T = 0.15), the jet flow starts to develop at the post-stenosis region. As the flow rate increases, the recirculation regions develop at t/T = 0.25. At t/T = 0.39, the length of the jet reaches the maximum at the peak flow rate. At this point, the swirling flow condition has a shorter jet flow length and a smaller recirculation flow area compared with the Poiseuille flow. At the diastole phase (0.39≤ t/T≤1.0), the recirculation flow at the swirling flow condition rapidly decreases along with the flow rate. On the contrary, the recirculation flow structure is maintained at t/T = 0.90 when the Poiseuille flow serves as an inlet to the stenosis. Figure 15a quantitatively presents the variations of phase-averaged flow reattachment length (L/D). The result shows that both of the maximum and mean L/D are reduced up to 1.0D by the introduction of the swirling flow. This clearly shows that the swirling flow inhibits the development of the recirculation flow structure at the post-stenosis under the physiological pulsatile flow condition. Since the retrograde flow in the recirculation area induces relatively high WSS oscillation during the pulsating cycle, the size of the recirculation flow is directly related to the area of high OSI distribution at the post-stenosis. Figure 15b presents the effect of pulsatile swirling flow on the OSI distribution at the post-steonsis. The results shows that the introduction of the swirling flow confines the high OSI region to X/D<2.5 while the Poiseuille flow induces causes the high OSI region up to X/D<4.

Bottom Line: Results showed that the swirling intensity and helicity of the swirling flow have a linear relation with a modified Germano number (Gn*) of the helical pipe.In addition, the swirling flow generated a beneficial flow structure at the stenosis by reducing the size of the recirculation flow under steady and pulsatile flow conditions.Therefore, the beneficial effects of a helical graft on the flow field can be estimated by using the magnitude of Gn*.

View Article: PubMed Central - PubMed

Affiliation: Department of Mechanical Engineering, Pohang University of Science and Technology (POSTECH), Pohang, Gyeongbuk, Republic of Korea.

ABSTRACT
Although a helical configuration of a prosthetic vascular graft appears to be clinically beneficial in suppressing thrombosis and intimal hyperplasia, an optimization of a helical design has yet to be achieved because of the lack of a detailed understanding on hemodynamic features in helical grafts and their fluid dynamic influences. In the present study, the swirling flow in a helical graft was hypothesized to have beneficial influences on a disturbed flow structure such as stenotic flow. The characteristics of swirling flows generated by helical tubes with various helical pitches and curvatures were investigated to prove the hypothesis. The fluid dynamic influences of these helical tubes on stenotic flow were quantitatively analysed by using a particle image velocimetry technique. Results showed that the swirling intensity and helicity of the swirling flow have a linear relation with a modified Germano number (Gn*) of the helical pipe. In addition, the swirling flow generated a beneficial flow structure at the stenosis by reducing the size of the recirculation flow under steady and pulsatile flow conditions. Therefore, the beneficial effects of a helical graft on the flow field can be estimated by using the magnitude of Gn*. Finally, an optimized helical design with a maximum Gn* was suggested for the future design of a vascular graft.

Show MeSH
Related in: MedlinePlus