Poster CC19 - Noninvasive optical imaging correlates to mechanical function in the posterior and anterior distal vaginal wall

Introduction: Pelvic organ prolapse (POP) is a multifaceted disease, with risk factors such as age and parity, that is characterized by the descent of the pelvic organs. Approximately 50% of women worldwide will develop POP stage two or higher; however, treatment is suboptimal with the United States reporting a surgical failure rate of 13% within two years of intervention and an estimated annual cost of $1 billion [1]. POP is caused by loss of pelvic floor integrity dictated by the extracellular matrix (ECM), and develops with increased frequency in the anterior vaginal compartment (34%) as compared to the posterior vaginal compartment (18%) [2]. Smooth muscle area fraction and longitudinal extensibility under uniaxial tension decrease in human vaginal tissue with POP; however, the correlation between biochemical and mechanical properties is not fully understood as indicated by conflicting reports [3,4]. Similarly, the physiological changes in the anterior and posterior vagina walls over time are largely under-researched. The lack of noninvasive assessments impedes the study of POP as biopsies are limited to the upper vaginal cuff and risk additional disease progression. Raman spectroscopy (RS) is a non-destructive optical technique sensitive to chemical composition that generates a molecular fingerprint from scattered incident light. The objective of this study was to leverage RS for vaginal wall assessment and determine the correlation between tissue extensibility and composition.

Materials and

Methods: Specimens without visually observed prolapse were resected from the anterior and posterior distal vaginal walls (Fig. 1A-B) of five cadavers (56-65 years old). Benchtop compositional evaluations were conducted with a probe-based near infrared RS system in twenty unique regions of interest (Fig. 1C). Spectra from a database of pure samples, including vaginal components that directly dictate structural integrity such as collagen, smooth muscle actin, and glycogen were input into a mathematical model to extract scores associated with each compound’s presence in the tissue. These scores were then displayed in a heatmap and benchmarked against histological analysis for validation (Fig. 1E).

The specimens were then subjected to equibiaxial planar tensile testing to quantify vaginal extensibility (Fig. 1D). The device stretched the tissue from a preload of 10mN to a target stress of 50kPa simultaneously in the circumferential and longitudinal directions. The tissue was subjected to 25 preconditioning cycles to acquire a consistent, repeatable, and mathematically interpretable measurement. After a ten-minute equilibration, another six cycles were performed, and the peak Green-Lagrangian strain map in the longitudinal direction during the last unloading cycle was analyzed using MATLAB [5].

Wilcoxon signed rank tests were performed on the acquired data to test the hypothesis that mechanical and compositional properties of the anterior and posterior vaginal walls differ in each patient. Heatmaps of the calculated optical signatures and the peak longitudinal strain were generated for each tissue in a centralized region of interest for two-dimensional correlation analysis (Fig. 1F).

Results, Conclusions, and Discussions: First, paired analysis evaluated if vaginal extensibility and ECM optical signatures differed in the anterior wall compared to the posterior walls of each cadaver (Fig. 1G). For all five cadavers, vaginal extensibility (p < 0.0001) and ECM component signatures (p < 0.01) differed between the anterior and posterior walls. Additionally, in four cadavers, vaginal extensibility was higher in the anterior wall compared to the posterior, similar to the reported behavior of non-POP human tissue [6]. The fifth cadaver exhibited opposing results, which may be due to mild prolapse not captured during visual evaluation [6]. Actin and collagen contributions displayed an inverse relationship in each pair except for cadaver one where a significant lipid contribution was observed. Both collagen and smooth muscle content dictate vaginal stability, and POP progression is characterized by loss of actin and collagen remodeling [7,8]. Compositional differences in the anterior and posterior walls likely contribute to the higher rate of anterior wall POP. Next, two-dimensional analyses identified statistically significant correlations between longitudinal extensibility and composition in four cadavers; however, cadaver two did not display significant associations.

RS is an optical technique that can quantify the composition of the vaginal canal without a biopsy. Successful correlation of the changes between vaginal extensibility and noninvasive biochemical composition in paired anterior and posterior distal wall samples solidifies the clinical potential of the presented workflow. The association of extensibility and optical composition represents a unique opportunity to assist in informing medical decisions, detecting disease, and monitoring treatment. Due to the restricted supply of age-matched cadaver tissues, their variability in health status, and the study’s small group size, there is some uncertainty on the association between the ECM component concentration and the longitudinal tissue extensibility. Additionally, the increased risk of pelvic floor disorders and physiological changes in reproductive organs with age may contribute to the observed variability [9].

Future analysis of patient biopsies from the upper vaginal cuff using the established workflow will mitigate these limitations and increase overall understanding. These preliminary findings and the proposed protocol highlight the utility of RS to track tissue quality and strength without exacerbating disease progression or tissue dysfunction.

Acknowledgements (Optional):

References:
[1] Wu, J. M., et al., Obstet. Gynecol. (2014).
[2] Hendrix, S. L., et al., Am. J. Obstet. Gynecol. (2002).
[3] Boreham, M. K., et al., Am. J. Obstet. Gynecol. (2002).
[4] Lei, L., et al., Int. Urogynecol. J. (2007).
[5] Yang, J., et al., Exp. Mech. (2018).
[6] Martins, P., et al, Gynecol. Obstet. Inves. (2013).
[7] Vulic, M., et al., Eur. J. Obstet. Gynecol. Reprod. Biol. (2011).
[8] Boreham, M. K., et al., Am. J. Obstet. Gynecol. (2002).
[9] Winkler, I., et al., Cell (2024).

Funding:
UTD CoBRA (KSM; MFR)
UT Rising STARs Award (IJP)
AHA Second Century Early Faculty Independence Award (IJP)