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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 flow structure at the post-stenosis. (a) Pulsatile waveforms of the normalized velocity at the stenosis apex. The maximum Re, mean Re and Womersley number (α) of the flow are 860, 212 and 9.69, respectively. (b) Phase-averaged velocity waveform. Velocity contours and streamlines are shown at (c) t/T = 0.15, (d) t/T = 0.25, (e) t/T = 0.39, (f) t/T = 0.55, (g) t/T = 0.75, (h) t/T = 0.90. 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-g014: The effect of pulsatile swirling flow on flow structure at the post-stenosis. (a) Pulsatile waveforms of the normalized velocity at the stenosis apex. The maximum Re, mean Re and Womersley number (α) of the flow are 860, 212 and 9.69, respectively. (b) Phase-averaged velocity waveform. Velocity contours and streamlines are shown at (c) t/T = 0.15, (d) t/T = 0.25, (e) t/T = 0.39, (f) t/T = 0.55, (g) t/T = 0.75, (h) t/T = 0.90. The Poiseuille flow (upper) and swirling flow (lower) are generated by the straight and helical tubes (Rc/R0 = 0.6, H/R0 = 4).

Mentions: Figure 14a shows the pulsatile waveforms of the normalized velocity at the stenosis apex. The maximum Re, mean Re and the Womersley number (α) of the flow are 860, 212, and 9.69, respectively. The phase-averaged velocity waveform obtained by ensemble averaging 55 cycles is shown in figure 14b. Among the pulsating cycles, the velocity contours and streamlines at six different phases (t/T = 0.15, 0.25, 0.39, 0.55, 0.75 and 0.90) are presented in figure 14c–h.


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 flow structure at the post-stenosis. (a) Pulsatile waveforms of the normalized velocity at the stenosis apex. The maximum Re, mean Re and Womersley number (α) of the flow are 860, 212 and 9.69, respectively. (b) Phase-averaged velocity waveform. Velocity contours and streamlines are shown at (c) t/T = 0.15, (d) t/T = 0.25, (e) t/T = 0.39, (f) t/T = 0.55, (g) t/T = 0.75, (h) t/T = 0.90. 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

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

pone-0111047-g014: The effect of pulsatile swirling flow on flow structure at the post-stenosis. (a) Pulsatile waveforms of the normalized velocity at the stenosis apex. The maximum Re, mean Re and Womersley number (α) of the flow are 860, 212 and 9.69, respectively. (b) Phase-averaged velocity waveform. Velocity contours and streamlines are shown at (c) t/T = 0.15, (d) t/T = 0.25, (e) t/T = 0.39, (f) t/T = 0.55, (g) t/T = 0.75, (h) t/T = 0.90. The Poiseuille flow (upper) and swirling flow (lower) are generated by the straight and helical tubes (Rc/R0 = 0.6, H/R0 = 4).
Mentions: Figure 14a shows the pulsatile waveforms of the normalized velocity at the stenosis apex. The maximum Re, mean Re and the Womersley number (α) of the flow are 860, 212, and 9.69, respectively. The phase-averaged velocity waveform obtained by ensemble averaging 55 cycles is shown in figure 14b. Among the pulsating cycles, the velocity contours and streamlines at six different phases (t/T = 0.15, 0.25, 0.39, 0.55, 0.75 and 0.90) are presented in figure 14c–h.

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