Biomechanics and Electromyography Inassessing Female Stress Urinary Incontinence

Introduction: Stress urinary incontinence (SUI), the involuntary urinary leakage associated with increases in intra-abdominal pressure, has a prevalence of 25–50% in U.S. women and the number of those who will undergo surgery will increase by half in the next forty years. SUI negatively affects the patient’s quality of life and places a great burden to the society. The functional anatomy of the continence mechanism remains vaguely understood. Hence my dissertation aims at offering a complete description of the pelvic floor muscles (PFM), the key contributor to the continence, thorough biomechanical and neurophysiological approaches. Methods: The biomechanical approach involves the development of a subject-specific finite element (FE) model of the female pelvic floor region. Subsequent computer simulations are targeted at finding the most contributive muscle to the urethral support function and evaluating current treatment strategies using a mini-sling. The neurophysiological approach involves the implementation of a novel surface electromyography (EMG) probe to acquire bioelectrical information of PFMs and the assessment of their innervations in healthy subjects and patients. Results: An FE pelvic floor model was developed which incorporates 40+ anatomical structural in the pelvis, representing the most complete model in the field. Simulation results showed that the vaginal walls, puborectalis, and pubococcygeus are the most important structures and that mid-distal post-urethral implantation represents the optimal location. Innervation zones of PFMs have been successfully identified and described for multiple PFMs. An high-density surface EMG-based motor unit number estimation approach was developed, providing a novel tool to evaluate the condition of neurologically impaired PFM. Conclusions: The combined information greatly advances our understanding of the physiology of PFM and would lay a firm foundation to novel, non-invasive, patient-specific interventional strategies in the future.Biomedical Engineering, Department o

Biomechanical Analyses of Anterior Vaginal Wall Prolapse: MR Imaging and Computer Modeling Studies.

Pelvic organ prolapse is a distressing and debilitating condition for which 200,000 U.S. women will undergo surgery each year. Anterior vaginal prolapse (AVP), clinically referred to as “cystocele,” is the most common form of pelvic organ prolapse. The pathomechanics of cystocele remains poorly understood. In this dissertation, magnetic resonance (MR) imaging was used to help develop biomechanical models in order to test a new hypothesis related to the mechanism of cystocele formation. We hypothesized that the occurrence and magnitude of AVP cannot be explained by a single failure mechanism: rather, a defect has to be present in the levator ani muscle and/or more than one connective tissue site. In women with and without prolapse we found that the presence of a major levator ani muscle defect on MR images is associated with a 50% reduction in the cross-sectional area of the ventral portion of their levator ani muscle compared with those having intact levator ani (Chapter 2). Apical descent and vaginal length explained 77% of the variation in cystocele size (Chapter 3). A 2-D sagittal plane, lumped parameter model (Chapter 4) and a 3-D, subject-specific, anatomically accurate, finite element model (Chapter 5) were developed to analyze the effect on cystocele formation of different combinations of connective tissue and muscle impairments. The models suggest that a larger cystocele formed in the presence of both muscular and mesenteric connective tissue support impairments than with either support element impairment alone. In particular, an impaired levator ani muscle caused a larger hiatus size, longer exposed vaginal length, larger apical descent and resulted in larger cystocele size. Synchronous measurements of intra-abdominal pressure and displacements of the most dependent bladder point on dynamic MR images were used to make the first in vivo estimates of the compliance of anterior vaginal wall support (Chapter 6). Women with cystocele had 67% greater compliance of their support system compared to controls. This dissertation provides insights into the biomechanical mechanisms underlying the development of anterior vaginal wall prolapse. Hopefully, these insights will help lead to improvements in the treatment of this distressing condition.Ph.D.Biomedical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/61756/1/luyunc_1.pd

Modelling of Soft Connective Tissues to Investigate Female Pelvic Floor Dysfunctions

After menopause, decreased levels of estrogen and progesterone remodel the collagen of the soft tissues thereby reducing their stiffness. Stress urinary incontinence is associated with involuntary urine leakage due to pathological movement of the pelvic organs resulting from lax suspension system, fasciae, and ligaments. This study compares the changes in the orientation and position of the female pelvic organs due to weakened fasciae, ligaments, and their combined laxity. A mixture theory weighted by respective volume fraction of elastin-collagen fibre compound (5%), adipose tissue (85%), and smooth muscle (5%) is adopted to characterize the mechanical behaviour of the fascia. The load carrying response (other than the functional response to the pelvic organs) of each fascia component, pelvic organs, muscles, and ligaments are assumed to be isotropic, hyperelastic, and incompressible. Finite element simulations are conducted during Valsalva manoeuvre with weakened tissues modelled by reduced tissue stiffness. A significant dislocation of the urethrovesical junction is observed due to weakness of the fascia (13.89 mm) compared to the ligaments (5.47 mm). The dynamics of the pelvic floor observed in this study during Valsalva manoeuvre is associated with urethral-bladder hypermobility, greater levator plate angulation, and positive Q-tip test which are observed in incontinent females

Biomechanical Simulations of Human Pregnancy: Patient-Specific Finite Element Modeling

Preterm birth (PTB) is the leading cause of childhood death and effects 10% of babies worldwide. First-time diagnosis is difficult, and as many as 95% of all PTBs are intractable to current therapies. The processes of both preterm labor and normal parturition are poorly understood, in part because pregnancy is a protected environment where experimentation contains the risk of causing harm to the gestation and fetus. This proposes the need for non-invasive investigations to understand both normal and high-risk pregnancies. Furthermore, each pregnancy can vary significantly which adds the complex need for patient-specific investigations. To address this need, we propose the development of parameterized ultrasound-based finite element analyses to study the mechanics of the womb. As a first step, this dissertation work conducts sensitivity analyses on cervical, uterine, and fetal membrane parameters as well as model boundary conditions to determine which factors have the greatest impact on cervical tissue stretch. The effects of the range of patient geometries and material properties are reported. Findings show that a soft and short cervix result in greatest stretch at the internal os, and fetal membrane detachment increases cervical stretch. Additionally, patient-specific finite element analyses are performed on low- and high-risk cohorts and results between the two are compared. Patient geometries are documented at various gestational timepoints, and the effect of a cervical pessary is determined based on changes in cervical geometry and stiffness. Findings showed that a soft cervix correlates with sooner delivery, and that high pessary placement is ideal to decrease stretch at the internal os

Book of Abstracts 15th International Symposium on Computer Methods in Biomechanics and Biomedical Engineering and 3rd Conference on Imaging and Visualization

In this edition, the two events will run together as a single conference, highlighting the strong connection with the Taylor & Francis journals: Computer Methods in Biomechanics and Biomedical Engineering (John Middleton and Christopher Jacobs, Eds.) and Computer Methods in Biomechanics and Biomedical Engineering: Imaging and Visualization (JoãoManuel R.S. Tavares, Ed.). The conference has become a major international meeting on computational biomechanics, imaging andvisualization. In this edition, the main program includes 212 presentations. In addition, sixteen renowned researchers will give plenary keynotes, addressing current challenges in computational biomechanics and biomedical imaging. In Lisbon, for the first time, a session dedicated to award the winner of the Best Paper in CMBBE Journal will take place. We believe that CMBBE2018 will have a strong impact on the development of computational biomechanics and biomedical imaging and visualization, identifying emerging areas of research and promoting the collaboration and networking between participants. This impact is evidenced through the well-known research groups, commercial companies and scientific organizations, who continue to support and sponsor the CMBBE meeting series. In fact, the conference is enriched with five workshops on specific scientific topics and commercial software.info:eu-repo/semantics/draf

On the Mechanism of Levator Ani Muscle Injury during Vaginal Birth.

Vaginal birth is the single largest modifiable risk factor for female pelvic floor disorders, such as pelvic organ prolapse and excretory incontinence. Defects in the levator ani muscle (LA) near its pubic origin immediately after vaginal birth are known to correlate with a three-fold increase in prolapse later in life. A current knowledge gap concerns the normal anatomy, the detailed injury mechanism of this specific injury region, and accurate measures of second stage labor events. An anatomical study of the origin of the pubovisceral portion of the levator ani muscle (PVM) revealed a systematic change in morphology (Ch. 2.1): the medial origin formed a direct oblique attachment, while the lateral origin arose from the catenary-like levator arch. The fiber directions of the different LA subdivisions were quantified using MRIs (Ch. 2.2). The projected angle of the PVM fibers was found to differ by an average of 58° from that of the puborectal muscle (PRM) in the mid-sagittal plane, suggesting different mechanical roles in the pelvic floor structure. Another histological study revealed that the PVM originates medially from the PB via a fibrous entheses tangentially from the periosteum of the PB (Ch. 2.3). A 2-D simplified FE model representing the PVM showed a significant strain energy concentration at the inferior margin of the scarf enthesis (Ch. 3.1). This suggests why injury of the LA can initiate at that location. A 3-D FE model of vaginal birth corroborated these findings and demonstrated why not only the PVM origin (or enthesis) but also the levator arch were at higher risk of injury than the midsection (Ch. 3.2). Finally, a novel computer vision measurement system was developed for measuring perineal surface deformation during late second stage of labor (Ch. 4). The results from two women showed that the deformation during the final push was up to twice that of earlier pushes. We conclude that during vaginal birth, not only excessive stretch particularly at the end of the second stage but also characteristic anatomical pattern of the PVM origin play major roles in causing the injury.PHDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/97914/1/jinyongk_1.pd

Biomechanics of the pelvic floor during vaginal delivery

Tese de doutoramento. Engenharia Mecânica. Faculdade de Engenharia. Universidade do Porto, Instituto Superior Técnico. Universidade de Lisboa, Faculdade de Medicina. Universidade do Porto. 200