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Research Papers

Three-Dimensional Numerical Simulations of Peristaltic Contractions in Obstructed Ureter Flows

[+] Author and Article Information
Zahra Najafi

Department of Biomedical Engineering,
University of Akron,
Akron, OH 44325
e-mail: zn3@zips.uakron.edu

Prashanta Gautam

Department of Mechanical Engineering,
University of Akron,
Akron, OH 44325
e-mail: pg37@zips.uakron.edu

Bradley F. Schwartz

Division of Urology,
Southern Illinois University School of Medicine,
Springfield, IL 62702
e-mail: bschwartz@siumed.edu

Abhilash J. Chandy

Associate Professor
Department of Mechanical Engineering,
University of Akron,
Akron, OH 44325
e-mail: achandy@uakron.edu

Ajay M. Mahajan

Professor
Department of Biomedical Engineering,
University of Akron,
Akron, OH 44325
e-mail: majay@uakron.edu

1Corresponding author.

Manuscript received January 12, 2016; final manuscript received July 12, 2016; published online August 18, 2016. Assoc. Editor: Keefe B. Manning.

J Biomech Eng 138(10), 101002 (Aug 18, 2016) (7 pages) Paper No: BIO-16-1014; doi: 10.1115/1.4034307 History: Received January 12, 2016; Revised July 12, 2016

Ureteral peristalsis can be considered as a series of waves on the ureteral wall, which transfers the urine along the ureter toward the bladder. The stones that form in the kidney and migrate to the ureter can create a substantial health problem due to the pain caused by interaction of the ureteral walls and stones during the peristaltic motion. Three-dimensional (3D) computational fluid dynamics (CFD) simulations were carried out using the commercial code ansys fluent to solve for the peristaltic movement of the ureter, with and without stones. The effect of stone size was considered through the investigation of varying obstructions of 5%, 15%, and 35% for fixed spherical stone shape. Also, an understanding of the effect of stone shape was obtained through separate CFD calculations of the peristaltic ureter with three different types of stones, a sphere, a cube, and a star, all at a fixed obstruction percentage of 15%. Velocity vectors, mass flow rates, pressure gradients, and wall shear stresses were analyzed along one bolus of urine during peristalsis of the ureteral wall to study the various effects. It was found that the increase in obstruction increased the backflow, pressure gradients, and wall shear stresses proximal to the stone. On the other hand, with regard to the stone shape study, while the cube-shaped stones resulted in the largest backflow, the star-shaped stone showed highest pressure gradient magnitudes. Interestingly, the change in stone shape did not have a significant effect on the wall shear stress at the obstruction level studied here.

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References

Figures

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Fig. 1

Geometrical model for the ureter; location A represents the location of different shapes and sizes of stones; also indicated in the figure are the pressure boundary conditions, Pin and Pout representing the proximal and distal ends, respectively, with Pin>Pout

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Fig. 2

Initial computational mesh for the ureter model

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Fig. 3

Velocity vectors for the spherical stones (a) 5% ureteral obstruction at time T/4, (b) 15% ureteral obstruction at time T/4, (c) 35% ureteral obstruction at time T/4, (d) 5% ureteral obstruction at time 3T/4, (e) 15% ureteral obstruction at time 3T/4, and (f) 35% ureteral obstruction at time 3T/4. (The proximal part of the ureter is on the left side of each figure and the distal is on the right).

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Fig. 4

Backflow at the inlet (proximal to the stone) in the 35% stone obstruction case. The backflow velocity is the highest in the vicinity of the stone.

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Fig. 5

Calculations of (a) mass flow rate and (b) percentage change of mass flow rate from the unobstructed case, at the inlet of the ureter in the direction of the flow, for varying obstructions, at times T/4, T/2, 3T/4, and T

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Fig. 6

Pressure gradient magnitude of the spherical stones along the axis of the ureter at time T/4

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Fig. 7

Wall shear stress for different obstruction cases at time T/4

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Fig. 8

Velocity vectors for the different shapes of stones (a) spherical stone at time T/4, (b) cubical stone at time T/4, and (c) star-shaped stone at time T/4

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Fig. 9

Calculations of (a) mass flow rate and (b) percentage change of mass flow rate from the unobstructed case, at the inlet of the ureter in the direction of the flow, for varying stones shapes, at times T/4, T/2, 3T/4, and T

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Fig. 10

Pressure gradient magnitudes of the different shapes of the stones at time T/4

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Fig. 11

Wall shear stress for different shapes of the stones at time T/4

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