Investigation of Murine Vaginal Creep Response to Altered Mechanical Loads

The vagina is a viscoelastic fibromuscular organ that provides support to the pelvic organs. The viscoelastic properties of the vagina are understudied but may be critical for pelvic stability. Most studies evaluate vaginal viscoelasticity under a single uniaxial load; however, the vagina is subjected to dynamic multiaxial loading in the body. It is unknown how varied multiaxial loading conditions affect vaginal viscoelastic behavior and which microstructural processes dictate the viscoelastic response. Therefore, the objective was to develop methods using extension-inflation protocols to quantify vaginal viscoelastic creep under various circumferential and axial loads. Then, the protocol was applied to quantify vaginal creep and collagen microstructure in the fibulin-5 wildtype and haploinsufficient vaginas. To evaluate pressure-dependent creep, the fibulin-5 wildtype and haploinsufficient vaginas (n = 7/genotype) were subjected to various constant pressures at the physiologic length for 100 s. For axial length-dependent creep, the vaginas (n = 7/genotype) were extended to various fixed axial lengths then subjected to the mean in vivo pressure for 100 s. Second-harmonic generation imaging was performed to quantify collagen fiber organization and undulation (n = 3/genotype). Increased pressure significantly increased creep strain in the wildtype, but not the haploinsufficient vagina. The axial length did not significantly affect the creep rate or strain in both genotypes. Collagen undulation varied through the depth of the subepithelium but not between genotypes. These findings suggest that the creep response to loading may vary with biological processes and pathologies, therefore, evaluating vaginal creep under various circumferential loads may be important to understand vaginal function.

Role of fibulin-5 insufficiency and prolapse progression on murine vaginal biomechanical function

The vagina plays a critical role in supporting the pelvic organs and loss of support leads to pelvic organ prolapse. It is unknown what microstructural changes influence prolapse progression nor how decreased elastic fibers contributes to vaginal remodeling and smooth muscle contractility. The objective for this study was to evaluate the effect of fibulin-5 haploinsufficiency, and deficiency with progressive prolapse on the biaxial contractile and biomechanical function of the murine vagina. Vaginas from wildtype (n = 13), haploinsufficient (n = 13), and deficient mice with grade 1 (n = 9) and grade 2 or 3 (n = 9) prolapse were explanted for biaxial contractile and biomechanical testing. Multiaxial histology (n = 3/group) evaluated elastic and collagen fiber microstructure. Western blotting quantified protein expression (n = 6/group). A one-way ANOVA or Kruskal-Wallis test evaluated statistical significance. Pearson's or Spearman's test determined correlations with prolapse grade. Axial contractility decreased with fibulin-5 deficiency and POP (p < 0.001), negatively correlated with prolapse grade (ρ = - 0.80; p < 0.001), and positively correlated with muscularis elastin area fraction (ρ = - 0.78; p = 0.004). Circumferential (ρ = 0.71; p < 0.001) and axial (ρ = 0.69; p < 0.001) vaginal wall stresses positively correlated with prolapse grade. These findings demonstrated that fibulin-5 deficiency and prolapse progression decreased vaginal contractility and increased vaginal wall stress. Future work is needed to better understand the processes that contribute to prolapse progression in order to guide diagnostic, preventative, and treatment strategies.

Comparison of Biaxial Biomechanical Properties of Post-menopausal Human Prolapsed and Non-prolapsed Uterosacral Ligament

Uterosacral ligaments (USLs) provide structural support to the female pelvic floor, and a loss of USL structural integrity or biomechanical function may induce pelvic organ prolapse (POP). Alterations in extracellular matrix composition and organization dictate USL mechanical function. Changes in USL microstructure and corresponding mechanical properties, however, are not fully understood, nor is it understood how microstructure and mechanics change with onset and progression of POP. This is due, in part, as USL properties are primarily characterized along a single direction (uniaxial test), whereas the USL is loaded in multiple directions simultaneously within the body. Biaxial testing permits the acquisition of biomechanical data from two axes simultaneously, and thus simulates a more physiologic assessment compared to the traditional uniaxial testing. Therefore, the objective of this study was to quantify the biaxial biomechanical properties and histological composition of the USL in post-menopausal women with and without POP at various stages. Potential correlations between tissue microstructural composition and mechanical function were also examined. Tangential modulus was lower and peak stretch higher in POP III/IV compared to non-POP and POP I/II in the main in vivo loading direction; however, no significant differences in mechanical properties were observed in the perpendicular loading direction. Collagen content positively correlated to tangential modulus in the main in vivo loading direction (r = 0.5, p = 0.02) and negatively correlated with the peak stretch in both the main in vivo (r = -0.5, p = 0.02) and perpendicular loading directions (r = -0.3, p = 0.05). However, no statistically significant differences in USL composition were observed, which may be due to the small sample size and high variability of small sections of human tissues. These results provide first step towards understanding what microstructural and mechanical changes may occur in the USL with POP onset and progression. Such information may provide important future insights into the development of new surgical reconstruction techniques and graft materials for POP treatment.

Smooth muscle regional contribution to vaginal wall function

Pelvic organ prolapse is characterized as the descent of the pelvic organs into the vaginal canal. In the USA, there is a 12% lifetime risk for requiring surgical intervention. Although vaginal childbirth is a well-established risk factor for prolapse, the underlying mechanisms are not fully understood. Decreased smooth muscle organization, composition and maximum muscle tone are characteristics of prolapsed vaginal tissue. Maximum muscle tone of the vaginal wall was previously investigated in the circumferential or axial direction under uniaxial loading; however, the vaginal wall is subjected to multiaxial loads. Further, the contribution of vaginal smooth muscle basal (resting) tone to mechanical function remains undetermined. The objectives of this study were to determine the contribution of smooth muscle basal and maximum tone to the regional biaxial mechanical behaviour of the murine vagina. Vaginal tissue from C57BL/6 mice was subjected to extension-inflation protocols (n = 10) with and without basal smooth muscle tone. Maximum tone was induced with KCl under various circumferential (n = 5) and axial (n = 5) loading conditions. The microstructure was visualized with multiphoton microscopy (n = 1), multiaxial histology (n = 4) and multiaxial immunohistochemistry (n = 4). Smooth muscle basal tone decreased material stiffness and increased anisotropy. In addition, maximum vaginal tone was decreased with increasing intraluminal pressures. This study demonstrated that vaginal muscle tone contributed to the biaxial mechanical response of murine vaginal tissue. This may be important in further elucidating the underlying mechanisms of prolapse, in order to improve current preventative and treatment strategies.

Biaxial biomechanical properties of the nonpregnant murine cervix and uterus

From a biomechanical perspective, female reproductive health is an understudied area of research. There is an incomplete understanding of the complex function and interaction between the cervix and uterus. This, in part, is due to the limited research into multiaxial biomechanical functions and geometry of these organs. Knowledge of the biomechanical function and interaction between these organs may elucidate etiologies of conditions such as preterm birth. Therefore, the objective of this study was to quantify the multiaxial biomechanical properties of the murine cervix and uterus using a biaxial testing set-up. To accomplish this, an inflation-extension testing protocol (n = 15) was leveraged to quantify biaxial biomechanical properties while preserving native matrix interactions and geometry. Ultrasound imaging and histology (n = 10) were performed to evaluate regional geometry and microstructure, respectively. Histological analysis identified a statistically significant greater collagen content and significantly smaller smooth muscle content in the cervix as compared to the uterus. No statistically significant differences in elastic fibers were identified. Analysis of bilinear fits revealed a significantly stiffer response from the circumferentially orientated ECM fibers compared to axially orientated fibers in both organs. Bilinear fits and a two-fiber family constitutive model showed that the cervix was significantly less distensible than the uterus. We submit that the regional biaxial information reported in this study aids in establishing an appropriate reference configuration for mathematical models of the uterine-cervical complex. Thus, may aid future work to elucidate the biomechanical mechanisms leading to cervical or uterine conditions.

Effects of elastase digestion on the murine vaginal wall biaxial mechanical response

Although the underlying mechanisms of pelvic organ prolapse (POP) remain unknown, disruption of elastic fiber metabolism within the vaginal wall extracellular matrix has been highly implicated. It has been hypothesized that elastic fiber fragmentation correlates to decreased structural integrity and increased risk of prolapse; however, the mechanisms by which elastic fiber damage may contribute to prolapse are poorly understood. Further, the role of elastic fibers in normal vaginal wall mechanics has not been fully ascertained. Therefore, the objective of this study is to investigate the contribution of elastic fibers to murine vaginal wall mechanics. Vaginal tissue from C57BL/6 female mice were mechanically tested using biaxial extension-inflation protocols before and after intraluminal exposure to elastase. Elastase digestion induced marked changes in the vaginal geometry, and biaxial mechanical properties, suggesting that elastic fibers may play an important role in vaginal wall mechanical function. Additionally, a constitutive model that considered two diagonal families of collagen fibers with a slight preference towards the circumferential direction described the data reasonably well before and after digestion. The present findings may be important to determine the underlying structural and mechanical mechanisms of POP, and aid in the development of growth and remodeling models for improved assessment and prediction of changes in structure-function relationships with prolapse development. Keywords: vaginal wall, women's health, mechanical testing, pelvic floor disorders, elastic fibers Disclosures: none.

Cervical pathways for racial disparities in preterm births: the Preterm Prediction Study

Purpose: Racial disparities in preterm birth have been long recognized, but the social and biological mechanisms for these differences are unclear. Our analysis had three goals: (1) to determine the relation between race and other social risk factors and cervical structure; (2) to determine whether social factors mediate the relation between race and cervical structure; and (3) to determine whether racial disparities in preterm birth (PTB) are mediated through changes in cervical structure observed earlier in pregnancy. Materials and methods: Data from the Maternal Fetal Medicine Unit network Preterm Prediction Study were used to examine the relation between race and other social factors and cervical properties throughout pregnancy in 2920 black and white women. Outcomes included cervical length and dilation; cervical score (cervical length-internal dilation); and whether membranes protruded at 22-24 and 26-29 weeks. Race, education, income, insurance type, and marital status were examined as predictors of the outcomes using linear and logistic regression, adjusting for age, BMI, parity, and smoking. Mediation analysis was used to examine whether (a) any social factors explained racial differences in cervical properties, and (b) whether cervical properties mediated racial differences in risk for preterm birth. Results: Shorter cervical length, especially at a subject's first visit, was associated with black race (adjusted beta -1.56 mm, p < .01) and lower income (adjusted beta -1.48, p =.05). External dilation was not associated with social factors, while internal dilation was associated with black race and lower education. Black race and marital status were associated with lower cervical score. There was no evidence of mediation of the racial effect on cervical properties by any social factor. Shorter cervical length, dilation, and score were all associated with preterm birth (p < .01). Mediation analysis indicated that each of these mediated the effect of race, but explained a small proportion of the total effect (15-25%). Conclusions: Race, and, to a lesser extent, other social factors are correlated with adverse cervical properties. This pathway could explain a proportion of the racial disparity in preterm birth.

Biaxial Mechanical Assessment of the Murine Vaginal Wall Using Extension-Inflation Testing

Progress toward understanding the underlying mechanisms of pelvic organ prolapse (POP) is limited, in part, due to a lack of information on the biomechanical properties and microstructural composition of the vaginal wall. Compromised vaginal wall integrity is thought to contribute to pelvic floor disorders; however, normal structure-function relationships within the vaginal wall are not fully understood. In addition to the information produced from uniaxial testing, biaxial extension-inflation tests performed over a range of physiological values could provide additional insights into vaginal wall mechanical behavior (i.e., axial coupling and anisotropy), while preserving in vivo tissue geometry. Thus, we present experimental methods of assessing murine vaginal wall biaxial mechanical properties using extension-inflation protocols. Geometrically intact vaginal samples taken from 16 female C57BL/6 mice underwent pressure-diameter and force-length preconditioning and testing within a pressure-myograph device. A bilinear curve fit was applied to the local stress-stretch data to quantify the transition stress and stretch as well as the toe- and linear-region moduli. The murine vaginal wall demonstrated a nonlinear response resembling that of other soft tissues, and evaluation of bilinear curve fits suggests that the vagina exhibits pseudoelasticity, axial coupling, and anisotropy. The protocols developed herein permit quantification of biaxial tissue properties. These methods can be utilized in future studies in order to assess evolving structure-function relationships with respect to aging, the onset of prolapse, and response to potential clinical interventions.

Racial and social predictors of longitudinal cervical measures: the Cervical Ultrasound Study

OBJECTIVE

To evaluate whether the racial and socioeconomic disparities are present in adverse cervical parameters, and, if so, when such disparities develop.

STUDY DESIGN

A prospective cohort study was conducted. 175 women with a prior preterm birth had up to four endovaginal ultrasounds between gestational weeks 16 and 24 (Cervical Ultrasound Trial of the MFMU). Each sociodemographic factor (race/ethnicity, marital status, insurance funding and education) was examined as a predictor of short cervix or U/funnel shape, using multiple logistic and linear regression. Changes in the cervical length and shape across pregnancy and after pressure were also examined.

RESULTS

The strongest associations were seen between race and government-funded insurance and short cervix and U shape per funneling (race and length <25 mm per funnel: adjusted odds ratio (OR) 5.52, 2.24 to 13.63; government-funded insurance and length <30 mm per funnel: adjusted OR 3.10, 1.34 to 7.15). Changes in cervical length were not associated with sociodemographics.

CONCLUSION

African-American race and, to a lesser extent, insurance funder, are associated with cervical length and shapes that have been associated with preterm birth, and those properties are present largely early in pregnancy.

Increased morbidity in combined abdominal sacrocolpopexy and abdominoplasty procedures

INTRODUCTION AND HYPOTHESIS

This study was performed to determine whether abdominoplasty combined with abdominal sacrocolpopexy (ASC + A) increases perioperative morbidity compared with ASC alone. We hypothesized that patients undergoing combined procedures would have increased complications.

METHODS

This was a multicenter, retrospective cohort study of all women undergoing ASC + A from 2002 to 2010 at Washington Hospital Center and Johns Hopkins University. We selected two women undergoing ASC alone for comparison with each ASC + A patient. Baseline demographics, surgical data, length of hospitalization, and perioperative complications were recorded. The primary outcome was any major complication within 6 weeks of surgery, including intraoperative complications, pulmonary embolism (PE), deep venous thrombosis (DVT), cardiac compromise, intensive care unit (ICU) admission, reoperation, and readmission. Surgical data and minor complications were also compared.

RESULTS

Twenty-six ASC + A patients and 52 ASC patients were identified. There were no significant differences in baseline characteristics between groups. Patients with ASC + A had longer operating times (337 vs 261 min, p < 0.01), more intravenous fluid administration intraoperatively (4,665 vs 3181 ml, p < 0.01), and longer hospital stays (3.7 vs 2.7 days, p < 0.01). Major complications occurred in 23 % of the ASC + A group compared with 12 % of the ASC group (p = 0.20). The ASC + A group had greater declines in hematocrit levels and higher rates of PE, ICU admission, and blood transfusion, all of which were statistically significant.

CONCLUSIONS

ASC + A increases length of stay and perioperative complications, such as PE, ICU admission, and blood transfusion, compared with ASC alone. Surgeons should consider recommending interval abdominoplasty due to increased morbidity risk with a combined procedure.

Teaching subcuticular suturing to medical students: video versus expert instructor feedback

OBJECTIVE

Given limitations in surgical educational resources, more efficient teaching methods are needed. We sought to evaluate 3 strategies for improving skills in subcuticular suturing-practice with an instructional video, practice with expert instructor supervision, and independent practice.

DESIGN

Fifty-eight medical students volunteered for this research. Students viewed a video on subcuticular suturing then completed a pretest requiring closure of an incision in a plastic model. Students were randomized among 3 groups: practice with an instructional video (group A), practice with supervision by an expert instructor (group B), and independent practice (group C). After instruction, students completed a posttest, then a retention test 1 week later. Their performances were video recorded and evaluated using a validated scoring instrument composed of global and task-specific subscales.

RESULTS

Performances measured using both subscales improved significantly from pretest to post-test only for group B. However, when comparing student performances between pretest and retention posttest, significant improvements on both subscales were seen only in group A.

CONCLUSION

These results suggest that practice with an instructional video is an effective method for acquiring skill in subcuticular suturing.

Sexual complaints, pelvic floor symptoms, and sexual distress in women over forty

INTRODUCTION

The American Psychiatric Association recommends considering sexually related personal distress when assessing female sexual dysfunction. Currently, there is little data regarding the impact of sexual complaints on sexual distress.

AIM

To investigate the association between sexual complaints and perceived sexual distress in a population of ambulatory adult women.

METHODS

Using the short forms of the Personal Experiences Questionnaire and Pelvic Organ Prolapse/Urinary Incontinence Sexual Function Questionnaire, we assessed sexual complaints among 305 women seeking outpatient gynecologic care. Depressive symptoms were quantified using the Center for Epidemiologic Studies Depression (CESD) score. Sexual distress was measured using the Female Sexual Distress Scale (FSDS). Using multivariable logistic regression, we compared sexual complaints between distressed and nondistressed women.

MAIN OUTCOME MEASURES

Sexual distress, defined by FSDS score ≥15.

RESULTS

FSDS scores were available for 292/305 participants. Seventy-six (26%) scores reflected distress. Distressed women were more likely to be younger (55.2±1.0 years vs. 56.7±0.8 years, P=0.017); have higher CESD scores (16.6 vs. 9.5, P=0.001); and report decreased arousal (56.8% vs. 25.1%, P=0.001), infrequent orgasm (54% vs. 28.8%, P=0.001), and dyspareunia (39.7% vs. 10.6%, P=0.001). Women with sexual distress were also more likely to report sexual difficulty related to pelvic floor symptoms, including urinary incontinence with sexual activity (9% vs. 1.3%, P=0.005), sexual avoidance due to vaginal prolapse (13.9% vs. 1%, P=0.001), or sexual activity restriction due to fear of urinary incontinence (14.9% vs. 0.5%, P=0.001). After multivariate analysis, sexual distress was significantly associated with dyspareunia (odds ratio [OR] 3.11, P=0.008) and depression score (OR 1.05, P=0.006), and inversely associated with feelings of arousal during sex (OR 0.19, P=0.001).

CONCLUSION

Our results indicate that sexually related personal distress is significantly associated with dyspareunia, depressive symptoms, and decreased arousal during sexual activity. This contributes to our understanding of how sexual complaints may adversely affect women's quality of life.

Anatomic outcomes of abdominal sacrocolpopexy with or without paravaginal repair

INTRODUCTION AND HYPOTHESIS

We sought to compare rates of recurrent cystocele following sacrocolpopexy with and without paravaginal repair (PVR).

METHODS

This retrospective cohort study compared outcomes for patients undergoing sacrocolpopexy with (group A) and without (group B) concomitant PVR. Defining anterior failure as point Ba > or = -1 cm, we compared anatomic outcomes and reoperation rates for recurrence of cystocele.

RESULTS

One hundred seventy patients undergoing sacrocolpopexy had anterior wall prolapse at or beyond the hymen before surgery (62 in group A and 108 in group B). Ten (16.1%) patients in group A and 29 (26.9%) in group B experienced anterior wall prolapse to or beyond -1 cm (p = 0.13, power 0.38). Among these groups, one (1.6%) and five (4.6%) underwent reoperation for cystocele recurrence (p=0.42, power <0.3).

CONCLUSIONS

Despite the trend toward improved clinical outcomes, we were unable to detect a statistically significant difference with inclusion of PVR with sacrocolpopexy.