Finite Element Modeling of Stress Urinary Incontinence Mechanics

Stress urinary incontinence is characterized by the involuntary transurethral loss of urine caused by an increase in abdominal pressure in the absence of a bladder contraction that raises the vesical pressure to a level that exceeds urethral pressure. Adult women are most commonly affected by SUI which is believed to be caused in part by injuries to the pelvic floor sustained during childbirth. In spite of the large number of women affected by SUI, little is known about the mechanics associated with the maintenance of continence in women. In theory the mechanics underlying the mechanics of female continence can be investigated through the use of complex dynamic finite element models of the lower urinary tract and pelvic floor. However, several modeling challenges must be overcome to construct such a model. The work in this dissertation focused on overcoming the challenges associated with modeling the bladder and the urethra in the context of stress urinary incontinence and incorporating clinically obtained urodynamic data into these models. In the first part of the dissertation, the effect of varying the material properties of the bladder and the urethra on the vesical pressure predicted by the model was studied. The results indicated that the material properties of the bladder and urethra had minimal effect on the vescial pressure predicted by the model indicating that vesical pressure could not be utilized as the lone validation criteria in subsequent models. The second portion of the study focused on identifying a method that could be used to model the fluid structure interactions that occur as the urine contained within the bladder is forced into and through the urethral lumen and determining which parameters may affect the flow of urine through the urethra. The split operator form of the arbitrary lagrangian eulerian method was identified as a method that could be utilized to model these interactions. In addition, the results of the modeling effort suggest that the stiffness of the urethra, the pressure ap

Finite Element Modeling of Stress Urinary Incontinence Mechanics

Stress urinary incontinence is characterized by the involuntary transurethral loss of urine caused by an increase in abdominal pressure in the absence of a bladder contraction that raises the vesical pressure to a level that exceeds urethral pressure. Adult women are most commonly affected by SUI which is believed to be caused in part by injuries to the pelvic floor sustained during childbirth. In spite of the large number of women affected by SUI, little is known about the mechanics associated with the maintenance of continence in women. In theory the mechanics underlying the mechanics of female continence can be investigated through the use of complex dynamic finite element models of the lower urinary tract and pelvic floor. However, several modeling challenges must be overcome to construct such a model. The work in this dissertation focused on overcoming the challenges associated with modeling the bladder and the urethra in the context of stress urinary incontinence and incorporating clinically obtained urodynamic data into these models. In the first part of the dissertation, the effect of varying the material properties of the bladder and the urethra on the vesical pressure predicted by the model was studied. The results indicated that the material properties of the bladder and urethra had minimal effect on the vescial pressure predicted by the model indicating that vesical pressure could not be utilized as the lone validation criteria in subsequent models. The second portion of the study focused on identifying a method that could be used to model the fluid structure interactions that occur as the urine contained within the bladder is forced into and through the urethral lumen and determining which parameters may affect the flow of urine through the urethra. The split operator form of the arbitrary lagrangian eulerian method was identified as a method that could be utilized to model these interactions. In addition, the results of the modeling effort suggest that the stiffness of the urethra, the pressure ap

Image-Based Computational Fluid Dynamics in Blood Vessel Models: Toward Developing a Prognostic Tool to Assess Cardiovascular Function Changes in Prolonged Space Flights

One of NASA's objectives is to be able to perform a complete, pre-flight, evaluation of cardiovascular changes in astronauts scheduled for prolonged space missions. Computational fluid dynamics (CFD) has shown promise as a method for estimating cardiovascular function during reduced gravity conditions. For this purpose, MRI can provide geometrical information, to reconstruct vessel geometries, and measure all spatial velocity components, providing location specific boundary conditions. The objective of this study was to investigate the reliability of MRI-based model reconstruction and measured boundary conditions for CFD simulations. An aortic arch model and a carotid bifurcation model were scanned in a 1.5T Siemens MRI scanner. Axial MRI acquisitions provided images for geometry reconstruction (slice thickness 3 and 5 mm; pixel size 1x1 and 0.5x0.5 square millimeters). Velocity acquisitions provided measured inlet boundary conditions and localized three-directional steady-flow velocity data (0.7-3.0 L/min). The vessel walls were isolated using NIH provided software (ImageJ) and lofted to form the geometric surface. Constructed and idealized geometries were imported into a commercial CFD code for meshing and simulation. Contour and vector plots of the velocity showed identical features between the MRI velocity data, the MRI-based CFD data, and the idealized-geometry CFD data, with less than 10% differences in the local velocity values. CFD results on models reconstructed from different MRI resolution settings showed insignificant differences (less than 5%). This study illustrated, quantitatively, that reliable CFD simulations can be performed with MRI reconstructed models and gives evidence that a future, subject-specific, computational evaluation of the cardiovascular system alteration during space travel is feasible

Finite Element Modeling of Stress Urinary Incontinence Mechanics

Stress urinary incontinence is characterized by the involuntary transurethral loss of urine caused by an increase in abdominal pressure in the absence of a bladder contraction that raises the vesical pressure to a level that exceeds urethral pressure. Adult women are most commonly affected by SUI which is believed to be caused in part by injuries to the pelvic floor sustained during childbirth. In spite of the large number of women affected by SUI, little is known about the mechanics associated with the maintenance of continence in women. In theory the mechanics underlying the mechanics of female continence can be investigated through the use of complex dynamic finite element models of the lower urinary tract and pelvic floor. However, several modeling challenges must be overcome to construct such a model. The work in this dissertation focused on overcoming the challenges associated with modeling the bladder and the urethra in the context of stress urinary incontinence and incorporating clinically obtained urodynamic data into these models. In the first part of the dissertation, the effect of varying the material properties of the bladder and the urethra on the vesical pressure predicted by the model was studied. The results indicated that the material properties of the bladder and urethra had minimal effect on the vescial pressure predicted by the model indicating that vesical pressure could not be utilized as the lone validation criteria in subsequent models. The second portion of the study focused on identifying a method that could be used to model the fluid structure interactions that occur as the urine contained within the bladder is forced into and through the urethral lumen and determining which parameters may affect the flow of urine through the urethra. The split operator form of the arbitrary lagrangian eulerian method was identified as a method that could be utilized to model these interactions. In addition, the results of the modeling effort suggest that the stiffness of the urethra, the pressure ap

Real-world variability in the prediction of intracranial aneurysm wall shear stress: The 2015 International Aneurysm CFD Challenge

Purpose—Image-based computational fluid dynamics (CFD) is widely used to predict intracranial aneurysm wall shear stress (WSS), particularly with the goal of improving rupture risk assessment. Nevertheless, concern has been expressed over the variability of predicted WSS and inconsistent associations with rupture. Previous challenges, and studies from individual groups, have focused on individual aspects of the image-based CFD pipeline. The aim of this Challenge was to quantify the total variability of the whole pipeline. Methods—3D rotational angiography image volumes of five middle cerebral artery aneurysms were provided to participants, who were free to choose their segmentation methods, boundary conditions, and CFD solver and settings. Participants were asked to fill out a questionnaire about their solution strategies and experience with aneurysm CFD, and provide surface distributions of WSS magnitude, from which we objectively derived a variety of hemodynamic parameters. Results—A total of 28 datasets were submitted, from 26 teams with varying levels of self-assessed experience. Wide variability of segmentations, CFD model extents, and inflow rates resulted in interquartile ranges of sac average WSS up to 56%, which reduced to < 30% after normalizing by parent artery WSS. Sac-maximum WSS and low shear area were more variable, while rank-ordering of cases by low or high shear showed only modest consensus among teams. Experience was not a significant predictor of variability. Conclusions—Wide variability exists in the prediction of intracranial aneurysm WSS. While segmentation and CFD solver techniques may be difficult to standardize across groups, our findings suggest that some of the variability in image-based CFD could be reduced by establishing guidelines for model extents, inflow rates, and blood properties, and by encouraging the reporting of normalized hemodynamic parameters