Abstract and Introduction
Background: The mechanisms of the microenergy acoustic pulse (MAP) therapy on restoring structure and function of pelvic floor muscles (PFM) after simulated birth injury are not well understood.
Methods: A total 24 female Sprague-Dawley rats were randomly grouped into sham control (sham), vaginal balloon dilation and ovariectomy (VBDO), VBDO + β-aminopropionitrile (BAPN, an irreversible LOX inhibitor), and VBDO + BAPN and treated with MAP (n=6 in each group). The MAP therapy was administered 2 times per week for 4 weeks with 1-week washout, the functional and histological studies were conducted in all 24 rats. The viscoelastic behavior of the PFM, including iliococcygeus (IC) and pubococcygeus (PC), was examined with a biomechanical assay. The structure of the PFM was assessed by immunofluorescence and Masson's trichrome staining.
Results: The leak point pressure (LPP) assay demonstrated that the MAP therapy group had higher LPPs compared to that of VBDO and BAPN groups. In the sham group, the muscular stiffness (K) of IC muscle was significantly higher than that of PC muscle while the pelvic floor muscle rebound activity (MRA) of PC muscle was stronger than that of IC muscle (291.26±45.33 and 241.18±14.23 N/cm2, respectively). Both VBDO and BAPN decreased the MRA and increased the K in both IC and PC. Histologic examination revealed increased fibrous tissue (collagen) and degeneration of muscle fibers in both VBDO and BAPN groups. MAP therapy significantly reduced the collagen content and improved the architecture of muscle fibers.
Conclusions: MAP appears to restore the structure and function of PFM by regenerating muscular fibers and improving biomechanical properties in an animal model of simulated birth injury.
Stress urinary incontinence (SUI) affects about 167 million women worldwide (a prevalence of 3.3%),[1,2] with 45.9% of women in the United States reporting symptoms of SUI. Furthermore, pelvic organ prolapse (POP) has an estimated prevalence of 3–6%, and as high as 50% when evaluated based on vaginal examination alone.[1,4] Non-surgical treatment options for SUI and POP include the exercises of pelvic floor muscle, electric stimulation, and creams with different hormones. While these conservative therapies are pretty safe, the durability and efficacy are limited. In the US, the mainstay of surgical treatment for SUI is the mid-urethral sling, but can also include autologous fascial pubovaginal slings, urethral bulking, or colposuspension. For symptomatic POP, surgical procedures include repair with native tissue, abdominal sacrocolpopexy, and transvaginal mesh. Currently, the surgeries with meshes for both SUI and POP are very effective, but mesh exposure, infection, severe pelvic pain, and the dyspareunia are complications in the clinic. In the United States alone, those clinical complications have resulted in more than 140,000 lawsuits, and the complete cessation of transvaginal mesh kits for POP has been issued in the USA, in Australia, and in UK. At the same time, from July 2018, the mesh surgeries for SUI were also stopped in UK.
Awareness of mesh-related complications, interest in applying regenerative medicine approaches to restore the structure and function of urethral sphincter and pelvic floor was increased.[6–10] Currently, the stem cell therapy for SUI is dominated,[11–13] as well as the tissue engineering associated with stem cells for POP. However, extensive investigation before its clinical application is needed. Very recently, using products related to stem cells and the tissue-resident stem/progenitor cells[15,16] to enhance the regeneration process is another research hot topic.[10,17–19]
The pathophysiology of pelvic floor disorders (PFDs) such as SUI and POP is still unclear, but it has been demonstrated that involves genetic susceptibility, connective tissue abnormal, hormone effects, obesity, pregnancy, hysterectomy, constipation, and advanced age. It has been demonstrated that pelvic floor muscle dysfunction is a key factor in the development of PFDs. However, as muscle physiologists tend to study the behavior of contracting muscles, this focus on muscle contraction means that the research on the mechanical properties of relaxing muscles has been relatively neglected. The passive properties of muscles play a central role in various physiological and pathophysiological processes[21,22] and merit more attention and research.[23,24]
Many studies using low-energy shock waves on other organs have been published.[25,26] However, there are limited studies on the mechanobiological effects of the microenergy acoustic pulses (MAP) which is a modified low-intensity shock wave with a different wave form, on the bladder, urethra, and pelvic floor muscles (PFM).[27–30] In current study, we propose to further elucidate the molecular mechanisms involved.
This study aims to measure the passive biomechanical properties of PFM because the biomechanical properties of PFM affect their stretching range and position. In this current study, a stress-relaxation test on fresh rat pelvic floor muscle tissue was conducted, and the effects of MAP therapy on the structure and function of PFM was assessed. The following article is presented in accordance with the ARRIVE reporting checklist (available at https://tau.amegroups.com/article/view/10.21037/tau-22-30/rc).
Transl Androl Urol. 2022;11(5):595-606. © 2022 AME Publishing Company