On the variation in maternal birth canal in vivo viscoelastic properties and their effect on the predicted length of active second stage and levator ani tears.

The pubovisceral muscles (PVM) help form the distal maternal birth canal. It is not known why 13% of vaginal deliveries end in PVM tears, so insights are needed to better prevent them because their sequelae can lead to pelvic organ prolapse later in life. In this paper we provide the first quantification of the variation in in vivo viscoelastic properties of the intact distal birth canal in healthy nulliparous women using Fung's Quasilinear Viscoelastic Theory and a secondary analysis of data from a clinical trial of constant force birth canal dilation to 8 cm diameter in the first stage of labor in 26 nullipara. We hypothesized that no significant inter-individual variation would be found in the long time constant, τ2, which characterizes how long it takes the birth canal to be dilated by the fetal head. That hypothesis was rejected because τ2 values ranged 20-fold above and below the median value. These data were input to a biomechanical model to calculate how such variations affect the predicted length of the active second stage of labor as well as PVM tear risk. The results show there was a 100-fold change in the predicted length of active second stage for the shortest and longest τ2 values, with a noticeable increase for τ2 values over 1000 s. The correlation coefficent between predicted and observed second stage durations was 0.51. We conclude that τ2 is a strong theoretical contributor to the time a mother has to push in order to deliver a fetal head larger than her birth canal, and a weak predictor of PVM tear risk.

A constitutive model description of the in vivo material properties of lower birth canal tissue during the first stage of labor.

Remarkable changes must occur in the pelvic floor muscles and tissues comprising the birth canal to allow vaginal delivery. Despite these preparatory adaptations, approximately 13% of women who deliver vaginally for the first time (nulliparas) sustain tears near the origin of the pubovisceral muscle (PVM) which can result in pelvic organ prolapse later in life. To investigate why these tears occur, it is necessary to quantify the viscoelastic behavior of the term pregnant human birth canal. The goal of this study was to quantify the in vivo material properties of the human birth canal, in situ, during the first stage of labor and compare them to published animal data. The results show that pregnant human, ovine and squirrel monkey birth canal tissue can be characterized by the same set of constitutive relations; the interspecies differences were primarily explained by the long time constant, τ2, with its values of 555s, 1110s, and 2777s, respectively. Quantification of these viscoelastic properties should allow for improved accuracy of computer models aimed at understanding birth-related injuries.

Plexiform schwannoma: an unusual clitoral mass.

Acquired clitoral enlargement is a rare condition resulting from a variety of etiologies, including tumors and excess androgens. Few cases of nonmalignant schwannoma, a benign tumor of the peripheral nerve sheath, have been reported in the literature as causes of clitoral enlargement in patients without known neurofibromatosis. These painless, slow-growing tumors rarely recur once excised. We present the initial investigation of a patient with a large clitoral schwannoma and subsequent treatment with partial vulvectomy. The workup, including advanced pelvic imaging for diagnosis and surgical planning, as well as removal of the clitoral tumor with preservation of functional tissue and restoration of normal vulvar anatomy despite a large excision, is demonstrated.

A Geometric Capacity-Demand Analysis of Maternal Levator Muscle Stretch Required for Vaginal Delivery.

Because levator ani (LA) muscle injuries occur in approximately 13% of all vaginal births, insights are needed to better prevent them. In Part I of this paper, we conducted an analysis of the bony and soft tissue factors contributing to the geometric "capacity" of the maternal pelvis and pelvic floor to deliver a fetal head without incurring stretch injury of the maternal soft tissue. In Part II, we quantified the range in demand, represented by the variation in fetal head size and shape, placed on the maternal pelvic floor. In Part III, we analyzed the capacity-to-demand geometric ratio, g, in order to determine whether a mother can deliver a head of given size without stretch injury. The results of a Part I sensitivity analysis showed that initial soft tissue loop length (SL) had the greatest effect on maternal capacity, followed by the length of the soft tissue loop above the inferior pubic rami at ultimate crowning, then subpubic arch angle (SPAA) and head size, and finally the levator origin separation distance. We found the more caudal origin of the puborectal portion of the levator muscle helps to protect it from the stretch injuries commonly observed in the pubovisceral portion. Part II fetal head molding index (MI) and fetal head size revealed fetal head circumference values ranging from 253 to 351 mm, which would increase up to 11 mm upon face presentation. The Part III capacity-demand analysis of g revealed that, based on geometry alone, the 10th percentile maternal capacity predicted injury for all head sizes, the 25th percentile maternal capacity could deliver half of all head sizes, while the 50th percentile maternal capacity could deliver a head of any size without injury. If ultrasound imaging could be operationalized to make measurements of ratio g, it might be used to usefully inform women on their level of risk for levator injury during vaginal birth.

Vascular smooth muscle cell functional contractility depends on extracellular mechanical properties.

Vascular smooth muscle cells' primary function is to maintain vascular homeostasis through active contraction and relaxation. In diseases such as hypertension and atherosclerosis, this function is inhibited concurrent to changes in the mechanical environment surrounding vascular smooth muscle cells. It is well established that cell function and extracellular mechanics are interconnected; variations in substrate modulus affect cell migration, proliferation, and differentiation. To date, it is unknown how the evolving extracellular mechanical environment of vascular smooth muscle cells affects their contractile function. Here, we have built upon previous vascular muscular thin film technology to develop a variable-modulus vascular muscular thin film that measures vascular tissue functional contractility on substrates with a range of pathological and physiological moduli. Using this modified vascular muscular thin film, we found that vascular smooth muscle cells generated greater stress on substrates with higher moduli compared to substrates with lower moduli. We then measured protein markers typically thought to indicate a contractile phenotype in vascular smooth muscle cells and found that phenotype is unaffected by substrate modulus. These data suggest that mechanical properties of vascular smooth muscle cells' extracellular environment directly influence their functional behavior and do so without inducing phenotype switching.