Ureterovesical junction deformation during urine storage in the bladder and the effect on vesicoureteral reflux

Kalayeh, Kourosh; Fowlkes, J. Brian; Schultz, William W.; Sack, Bryan S.

doi:10.1016/j.jbiomech.2020.110123

Cited by 6 publications

(17 citation statements)

References 34 publications

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Section: Methodsmentioning

confidence: 99%

“…(C) A typical FE mesh and (D) its magnified view around the UVJ. The figures are adopted from our previous work 7 …”

Section: Methodsmentioning

confidence: 99%

“…We have recently developed a large deformation FE model simulating deformation of the bladder wall during urine storage. 7 A commercial FE solver, COMSOL Multiphysics®, with the "Nonlinear Structural Materials Module" under "Solid Mechanics" physics solves the system of nonlinear equations. In this section, a summary of this model is presented.…”

Section: Methodsmentioning

confidence: 99%

“…As discussed in our previous work, 7 the bladder wall is modeled as a single, time independent, homogeneous, incompressible and elastic layer under nonlinear, large deformation conditions with modulus of elasticity of E = 12.0 kPa. 8,9 The bladder wall in its reference state is defined as a perfect sphere with a straight elliptical cylindrical hole with a cross-sectional eccentricity of 0.98 as a UVJ.…”

Section: Methodsmentioning

confidence: 99%

“…Therefore, a small section of the bladder wall encompassing the UVJ is sufficient to be modeled. 7 The model is further simplified by symmetry on the spherical cap mid-plane, through the axis of the UVJ. The detrusor pressure (intravesical pressure abdominal pressure) is applied on the inner surface of the bladder while its outer surface remains stress free.…”

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confidence: 99%

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The 5:1 rule overestimates the needed tunnel length during ureteral reimplantation

Kalayeh

Fowlkes

Schultz

et al. 2020

Neurourology and Urodynamics

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Aims: Paquin asserts that in order for ureterovesical junctions (UVJs) to prevent reflux, the ureteral tunnel length-to-diameter ratio needs to be 5:1. We hypothesize that the surgical implementation of this observation results in an overestimation of the needed length-to-diameter ratio to prevent vesicoureteral reflux. Methods: With finite elements, we model the urine storage phase of the bladder under nonlinear conditions. In the reference state, the bladder is assumed to be a sphere with an oblique straight elliptical hole as the UVJ. Broad parametric studies on different length-to-diameter ratios are performed as the bladder volume increases from 10% to 110% capacity. Results: The capability of the UVJ to prevent reflux during storage depends on its length-to-diameter ratio. UVJs with larger length-to-diameter ratios lengthen and narrow as the bladder volume increases, causing the closure of the UVJ and rise in its flow resistance. Our model shows that the UVJ length-to-diameter ratio decreases as the bladder volume increases. The 5:1 ratio implemented at 80% capacity-approximate volume or bladder wall stretch during ureteroneocystostomy (UNC)-corresponds to 7:1 at the reference state-used by Paquin. The 5:1 ratio implemented at the reference state corresponds to 3:1 at 80% capacity. Conclusions: Our modeling results are consistent with Paquin's original observation on the significance of the UVJ length-to-diameter ratio in preventing reflux. They, however, indicate that the surgical implementation of this rule during UNC results in an overestimation of the requisite tunnel length-todiameter ratio to prevent reflux. They also suggest that the UVJ closure is due to the bladder wall deformation rather than the pressure.

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Section: Methodsmentioning

confidence: 99%

“…(C) A typical FE mesh and (D) its magnified view around the UVJ. The figures are adopted from our previous work 7 …”

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

mentioning

confidence: 99%

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The 5:1 rule overestimates the needed tunnel length during ureteral reimplantation

Kalayeh

Fowlkes

Schultz

et al. 2020

Neurourology and Urodynamics

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Numerical analysis of an obstacle motion in the human ureter using the dynamic mesh approach

Abbasian,

Maddahian

2024

Numer Methods Biomed Eng

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Peristalsis is a common motion in various biological systems, especially the upper urinary tract, where it plays a pivotal role in conveying urine from the kidneys to the bladder. Using computational fluid dynamics, this study aims to investigate the effect of various peristaltic parameters on the motion of an obstacle through a two‐dimensional ureter. Methodologically, Incompressible Navier–Stokes equations were utilized as the fluid domain's governing equations, and the Dynamic Mesh method (DM) was employed to simulate the peristaltic and obstacle motion. The peristaltic motion was modeled by a sinusoidal contraction wave propagating alongside the ureter at the physiological speed, and the motion of the obstruction through the ureter, which is caused by the fluid forces applied on its surface, was explored using the equation of Newton's second law. Various test cases of different shapes and sizes were supposed as kidney stones to understand the influence of the peristalsis properties on the stone removal process. The results show that the motion of the kidney stone is highly influenced by the gradient pressure force applied to its surface in the fluid domain. Moreover, investigating the effects of the peristaltic physical properties on the obstacle's motion indicates that the stone's motion is dependent on these parameters. Furthermore, this analysis provides insight into the peristaltic motion effects, assisting physicians in developing new medicines to facilitate the kidney stone removal process based on its shape and size.

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Peristalsis prevents ureteral dilation

Kalayeh,

Fowlkes,

Xie

et al. 2023

Neurourology and Urodynamics

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PurposeThe etiology of ureteral dilation in primary nonrefluxing, nonobstructing megaureters is still not well understood. Impaired ureteral peristalsis has been theorized as one of the contributing factors. However, ureteral peristalsis and its “normal” function is not well defined. In this study, using mathematical modeling techniques, we aim to better understand how ureteral peristalsis works. This is the first model to consider clinically observed, back‐and‐forth, cyclic wall longitudinal motion during peristalsis. We hypothesize that dysfunctional ureteral peristalsis, caused by insufficient peristaltic amplitudes (e.g., circular muscle dysfunction) and/or lack of ureteral wall longitudinal motion (e.g., longitudinal muscle dysfunction), promotes peristaltic reflux (i.e., retrograde flow of urine during an episode of peristalsis) and may result in urinary stasis, urine accumulation, and consequent dilation.MethodsBased on lubrication theory in fluid mechanics, we developed a two‐dimensional (planar) model of ureteral peristalsis. In doing so, we treated ureteral peristalsis as an infinite train of sinusoidal waves. We then analyzed antegrade and retrograde flows in the ureter under different bladder–kidney differential pressure and peristalsis conditions.ResultsThere is a minimum peristaltic amplitude required to prevent peristaltic reflux. Ureteral wall longitudinal motion decreases this minimum required amplitude, increasing the nonrefluxing range of peristaltic amplitudes. As an example, for a normal bladder–kidney differential pressure of 5 cmH2O, ureteral wall longitudinal motion increases nonrefluxing range of peristaltic amplitude by 65%. Additionally, ureteral wall longitudinal motion decreases refluxing volumetric flow rates. For a similar normal bladder pressure example of 5 cmH2O, refluxing volumetric flow rate decreases by a factor of 18. Finally, elevated bladder pressure, not only increases the required peristaltic amplitude for reflux prevention but it increases maximum refluxing volumetric flow rates. For the case without wall longitudinal motion, as bladder–kidney differential pressure increases from 5 to 40 cmH2O, minimum required peristaltic amplitude to prevent reflux increases by 40% while the maximum refluxing volumetric flow rate increases by approximately 100%.ConclusionThe results presented in this study show how abnormal ureteral peristalsis, caused by the absence of wall longitudinal motion and/or lack of sufficient peristaltic amplitudes, facilitates peristaltic reflux and retrograde flow. We theorize that this retrograde flow can lead to urinary stasis and urine accumulation in the ureters, resulting in ureteral dilation seen on imaging studies and elevated infection risk. Our results also show how chronically elevated bladder pressures are more susceptible to such refluxing conditions that could lead to ureteral dilation.

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Ureterovesical junction deformation during urine storage in the bladder and the effect on vesicoureteral reflux

Cited by 6 publications

References 34 publications

The 5:1 rule overestimates the needed tunnel length during ureteral reimplantation

The 5:1 rule overestimates the needed tunnel length during ureteral reimplantation

Numerical analysis of an obstacle motion in the human ureter using the dynamic mesh approach

Peristalsis prevents ureteral dilation

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