Kalayeh Kourosh, Fowlkes J Brian, Schultz William W, Sack Bryan S
Department of Urology, University of Michigan, Ann Arbor, MI, USA.
Department of Radiology, University of Michigan, Ann Arbor, MI, USA.
J Biomech. 2020 Dec 2;113:110123. doi: 10.1016/j.jbiomech.2020.110123. Epub 2020 Nov 10.
The motivation behind this study is to understand how ureterovesical junction (UVJ) deformation during urine storage in the bladder affects vesicoureteral reflux (VUR), when urine flows backward from the bladder toward the kidneys. Using nonlinear, large deformation finite element simulations, the deformation of the bladder wall during urine storage is modeled in this study. The bladder wall is assumed to be a homogeneous, isotropic, hyperelastic spherical shell with a finite thickness. The UVJ is defined as a straight elliptical cylindrical hole through the bladder wall at the reference configuration before inflation. Broad parametric studies on different UVJ configurations are performed as the bladder inner surface stretches by a factor of 2.2 from an initial radius corresponding to bladder volumes of 10% to slightly over physiologic capacity. For each considered UVJ configuration, a simple fluid analysis of the tunnel flow resistance compares different bladder inner surface stretch ratios. Our model shows that the deformation of the UVJ depends on its orientation with respect to the bladder wall radial and circumferential directions. We show that as the UVJ insertion angle increases, the UVJ cross section decreases and its tunnel length increases during urine storage causing the closure of the UVJ and a rise in its flow resistance. The modeling results indicate that UVJ closure could be explained by bladder wall deformation rather than the local differential pressure. Our findings are consistent with the accepted primary anti-reflux mechanism of the UVJ being dependent on the tunnel length-to-diameter ratio and consequently the UVJ insertion angle.
本研究的目的是了解膀胱储尿期间输尿管膀胱连接部（UVJ）的变形如何影响膀胱输尿管反流（VUR），即尿液从膀胱逆流至肾脏时的情况。本研究采用非线性、大变形有限元模拟对储尿期间膀胱壁的变形进行建模。膀胱壁被假定为具有有限厚度的均匀、各向同性、超弹性球壳。UVJ在充气前的参考构型下被定义为穿过膀胱壁的直椭圆形圆柱孔。当膀胱内表面从对应于膀胱容量10%的初始半径拉伸至略超过生理容量的2.2倍时，对不同UVJ构型进行了广泛的参数研究。对于每种考虑的UVJ构型，通过对隧道流动阻力进行简单的流体分析来比较不同的膀胱内表面拉伸率。我们的模型表明，UVJ的变形取决于其相对于膀胱壁径向和周向的方向。我们发现，随着UVJ插入角度增加，储尿期间UVJ的横截面减小，其隧道长度增加，导致UVJ关闭且流动阻力增加。建模结果表明，UVJ关闭可由膀胱壁变形而非局部压差来解释。我们的研究结果与公认的UVJ主要抗反流机制一致，即取决于隧道长度与直径之比，进而取决于UVJ插入角度。
