Faculdade de Engenharia da Universidade do Porto, Rua Dr. Roberto Frias, s/n, 4200 Porto, Portugal; INEGI - Instituto de Ciência e Inovação em Engenharia Mecânica e Engenharia Industrial, Rua Dr. Roberto Frias, 400, 4200 Porto, Portugal.
Faculdade de Engenharia da Universidade do Porto, Rua Dr. Roberto Frias, s/n, 4200 Porto, Portugal.
J Mech Behav Biomed Mater. 2018 Dec;88:120-126. doi: 10.1016/j.jmbbm.2018.08.011. Epub 2018 Aug 11.
Injuries sustained by the pelvic floor muscles during childbirth are one of the major risk factors for the development of pelvic floor dysfunctions. The ability to predict the loss of the tissue integrity and the most affected regions prior to the childbirth would represent a compelling difference in choosing the appropriate management of labour. Previous biomechanical studies, using the finite element method, were able to simulate a vaginal delivery and analyse the mechanical effects on the pelvic floor muscles during the passage of the foetus. Complementing these studies, the aim of this work is to improve the characterization of the pelvic floor muscles, by using an anisotropic visco-hyperelastic constitutive model, including a continuum mechanics damage model. Viscoelasticity is a key feature to obtain more realistic results since biological tissues present relaxation effects that allow larger deformations without damage. This work analyses the reaction forces and the loss of tissue integrity sustained by the pelvic floor and evaluates the effects of different durations of labour. A delaying pushing technique of rest and descend is also studied in this work. The results obtained showed that the reaction forces vary with the duration of labour, with higher force levels associated with higher stretch rates. The pubovisceral muscle is the most affected of the levator ani, presenting an affected region of approximately 30%. The relaxation properties of the tissue contribute to diminish the damage levels, supporting the theory of delayed pushing applied in the second stage of labour.
分娩时盆底肌肉损伤是盆底功能障碍发展的主要危险因素之一。在分娩前预测组织完整性的丧失和最受影响的区域将代表选择合适的分娩管理的显著差异。以前的生物力学研究使用有限元法模拟阴道分娩，并分析胎儿通过时盆底肌肉的力学效应。为了补充这些研究，这项工作的目的是通过使用各向异性粘弹性本构模型，包括连续介质力学损伤模型，来改善对盆底肌肉的特征描述。粘弹性是获得更真实结果的关键特征，因为生物组织具有松弛效应，允许更大的变形而不会损坏。这项工作分析了盆底承受的反作用力和组织完整性的丧失，并评估了不同分娩时间的影响。在这项工作中还研究了延迟推挤休息和下降的技术。结果表明，反作用力随分娩时间而变化，与较高的拉伸率相关的力水平较高。耻骨直肠肌是提肛肌中最受影响的，其受影响区域约为 30%。组织的松弛特性有助于降低损伤水平，支持第二产程中应用的延迟推挤理论。
