Urethral support in female urinary continence part 1: dynamic measurements of urethral shape and motion

Effect of Squeeze, Cough, and Strain on Dynamic Urethral Function in Nulligravid Asymptomatic Women: A Cross-Sectional Cohort Study

IMPORTANCE

In the past, urethral shape, mobility, and urodynamics have been used to retrospectively demonstrate correlations with stress urinary incontinence. Our previous work has shown a relationship between urethral function and shape in symptomatic women.

OBJECTIVE

This study aimed to characterize the effect of pelvic floor squeeze and strain maneuvers on urethral shapes and pressure in a cohort of patients without pelvic floor disorders.

STUDY DESIGN

In this cross-sectional study, volunteers underwent dynamic pelvic floor ultrasound examination, and a modified urodynamic study. Urethral length, thickness, and proximal and distal swing angles were measured at rest, squeeze, and strain. The midsagittal urethral walls were traced so that a statistical shape model could be performed. Means and standard deviations of imaging and urodynamic measures were calculated.

RESULTS

Data from 19 participants were analyzed. On average during squeeze compared with rest, urethral length increased by 6%, thickness decreased by 42% (distal, P < 0.001), 10% (middle), and urethral pressure increased by 14%. Opposite shape changes-length decreased by 10% ( P = 0.001), thickness increased by 57% (distal, P < 0.001), 20% (middle, P < 0.001)-and increased urethral mobility were observed during strain, with larger pressure increases occurring (29%, P < 0.001). Fifty-one percent of the total shape variance described the differences between maneuvers. These differences were statistically different between groups ( P < 0.001 for comparisons, all others P > 0.05).

CONCLUSIONS

Dynamic ultrasound and urodynamics allow for the establishment of baseline ranges in urethral metrics (2-dimensional measures, shape, and pressure) and how they are altered during maneuvers. These data can allow for a more objective identification of incontinence via ultrasound and urodynamic testing.

Simulation of the female pelvic mobility and vesical pressure changes employing fluid-structure interaction method

INTRODUCTION AND HYPOTHESIS

This study aims to develop a fluid-structural interaction (FSI) method to pinpoint the effects of pressure changes inside the bladder and their impact on the supporting structure and the urethra mobility.

METHODS

A physiological model of the nulliparous female pelvis, including the organs, supportive structures, and urine, was developed based on magnetic resonance images. Soft tissues with nonlinear hyperelastic material characteristics were modeled. The Navier-Stokes equations governing the fluid flow within the computational domain (urine) were solved. The urine and soft tissue interactions were simulated by the FSI method. The vesical pressure and its impact on the urethral mobility and supportive structures were investigated during the Valsalva maneuver. Moreover, the simulation results were validated by comparing with a urodynamic test and other research.

RESULTS

The results demonstrated that the vesical pressure simulated by the FSI method could predict the nonlinear behavior of the urodynamic test pressure. The urethra retropubic bladder neck and the bladder neck-pubic bone angle changed 58.92% and -55.76%, respectively. The retropubic urethral length distance changed by -48.74%. The error compared to the statistical results of other research is < 5%.

CONCLUSIONS

The total deformation and mobility of the urethra predicted by the FSI model were consistent with clinical observations in a subject. The urethra supports dependence on the tissues' mechanical properties, interaction between the tissues, and effect of urine fluid inside the bladder. This simulation effectively depicts the patterns of urethra mobility, which provides a better understanding of the behavior of the pelvic floor.

Morphological Variation in the Pelvic Floor Muscle Complex of Nulliparous, Pregnant, and Parous Women

Specific levator ani muscle imaging measures change with pregnancy and vaginal parity, though entire pelvic floor muscle complex (PFMC) shape variation related to pregnancy-induced and postpartum remodeling has never been quantified. We used statistical shape modeling to compute the 3D variation in PFMC morphology of reproductive-aged nulliparous, late pregnant, and parous women. Pelvic magnetic resonance images were collected retrospectively and PFMCs were segmented. Modes of variation and principal component scores, generated via statistical shape modeling, defined significant morphological variation. Nulliparous (have never given birth), late pregnant (3rd trimester), and parous (have given birth and not currently pregnant) PFMCs were compared via MANCOVA. The overall PFMC shape, mode 2, and mode 3 significantly differed across patient groups (p < 0.001, = 0.002, = 0.001, respectively). This statistical shape analysis described greater perineal and external anal sphincter descent, increased iliococcygeus concavity, and a proportionally wider mid-posterior levator hiatus in late pregnant compared to nulliparous and parous women. The late pregnant group was the most divergent, highlighting differences that likely reduce the mechanical burden of vaginal childbirth. This robust quantification of PFMC shape provides insight to pregnancy and postpartum remodeling and allows for generation of representative non-patient-specific PFMCs that can be used in biomechanical simulations.

Urethral support in female urinary continence part 2: a computational, biomechanical analysis of Valsalva

INTRODUCTION AND HYPOTHESIS

In Part 1, we observed urethral mechanics during Valsalva that oppose current continence theories. In this study, we utilize a finite element model to elucidate the role of supportive tissues on the urethra during Valsalva. By determining the sensitivity of urethral motion and deformations to variations in tissue stiffnesses, we formulate new hypotheses regarding mechanisms of urethral passive closure.

METHODS

Anatomy was segmented from a nulliparous, continent woman at rest. The model was tuned such that urethral motion during Valsalva matched that observed in that patient. Urethra and surrounding tissue material properties were varied using Latin hypercube sampling to perform a sensitivity analysis. As in Part 1, urethral length, proximal and distal swinging, and shape parameters were measured at peak Valsalva for 50 simulations, and partial rank correlation coefficients were calculated between all model inputs and outputs. Cumulative influence factors determined which tissue properties were meaningfully influential (≥ 0.5).

RESULTS

The material properties of the urethra, perineal membrane, bladder, and paraurethral connective tissues meaningfully influenced urethral motion, deformation, and shape. Reduction of the urethral stiffness and/or the perineal membrane soft constraint resulted in simulated urethral motions and shapes associated with stress urinary incontinence in Part 1.

CONCLUSIONS

The data from Parts 1 and 2 suggest that connective tissues guide the controlled swinging motion and deformation of the urethra needed for passive closure during Valsalva. The swinging and kinking quantified in Part 1 and simulated in Part 2 are inconsistent with current continence theories.