Browsing by Author "Huntington, Alyssa Joan"

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    Anisotropy of Passive and Active Rat Vagina under Biaxial Loading
    Huntington, Alyssa Joan (Virginia Tech, 2018-06-11)
    Pelvic organ prolapse, the decent of the pelvic organs from their normal anatomical position, is a common condition among women that is associated with mechanical alterations of the vaginal wall. In order to characterize the complex mechanical behavior of the vagina, we performed planar biaxial tests of vaginal specimens in both the passive (relaxed) and active (contracted) states. Specimens were isolated from virgin, female Long-Evans rats (n=16) and simultaneously stretched along the longitudinal direction (LD) and circumferential direction (CD) of the vagina. Tissue contraction was induced by electric field stimulation (EFS) at incrementally increasing values of stretch and, subsequently, by KCl. On average, the vagina was stiffer in the CD than in the LD (p<0.001). The mean maximum EFS-induced active stress was significantly higher in the CD than in the LD (p<0.001). On the contrary, the mean KCl-induced active stress was lower in the CD than in the LD (p<0.01). When comparing the mean maximum EFS-induced active stress to the mean KCl-induced active stress, no differences were found in the CD (p=0.404) but, in the LD, the mean active stress was much higher in response to the KCl stimulation (p<0.001). Collectively, these results demonstrate that the anisotropic behavior of the vaginal tissue is determined not only by the collagen and smooth muscle fiber organization but also by the innervation. The findings of this study may contribute to the development of more effective treatments for pelvic organ prolapse.
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    Functional and Morphological Characteristics of Smooth Muscle in the Rat Vagina
    Huntington, Alyssa Joan (Virginia Tech, 2021-06-15)
    The vagina is an essential organ of the female reproductive system that has been largely understudied in the field of biomechanics. The ability of the vagina to contract gives rise to a set of active mechanical properties that contribute to the complex function of this organ in-vivo. After briefly reviewing experimental studies on the active properties of the vagina, including the differences in contractility with respect to anatomic regions and orientations, neural pathways, life events, pelvic floor disorders, and surgical mesh treatment, we present our novel experimental studies that aim toward filling existing knowledge gaps on vaginal tissue morphology and contractile function of the vagina. First, we quantified the large heterogeneous deformations that the vagina experiences during contractions for the first time. For this study, vaginal specimens were subjected to isometric planar biaxial tests, during which they were induced to contract via KCl at four applied equi-biaxial stretches. The digital image correlation method was used to perform full-field strain analysis during each contraction. The vagina was found to have anisotropic contractile behavior, generating higher forces and experiencing higher magnitude strains along the longitudinal direction (LD) than along the circumferential direction (CD) during contractions. Then, we performed the first detailed quantification of the distribution and alignment of vaginal smooth muscle and nerves throughout the vagina. Toward this goal, vaginas from adult female rats were subjected to a tissue clearing and immunohistochemistry protocol. Tissue clearing increased the transparency of the specimens such that organs could be imaged without sectioning, thus preserving the 3D architecture of the tissue. This analysis revealed a bimodal distribution of muscle alignment angles, with a significantly higher proportion of muscle oriented along the LD than along the CD of the organ. The morphologic and functional properties of the smooth muscle within the healthy vagina need to be fully investigated so that detrimental alterations in vaginal contractility, such as those caused by pelvic floor disorders and current treatment strategies, can be prevented.