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abstract

38 - EFFECT OF MULTIPLE DELIVERIES ON BIOMECHANICAL PROPERTIES OF PELVIC ORGAN TISSUES

038

EFFECT OF MULTIPLE DELIVERIES ONBIOMECHANICAL PROPERTIES OF PELVIC ORGAN TISSUES

R. RYNKEVIC1, P. S.MARTINS 1, T. MASCARENHAS 2, A. A. FERNANDES 3;
1Faculdade de Engenharia da Univ.e do Porto, Porto,Portugal, 2Urogynecology Unit, Hosp. S.JOAO -Faculty OfMed. Univ Porto, Porto, Portugal, 3INEGI,Univ. of Porto,Porto, Portugal.

Introduction: The biomechanicalproperties of pelvic organ tissues undergo changes, during pregnancyand labour due to age and hormonal status factors among others [1].Around 50 % of parous women suffer from some degree of prolapse [2].The degree and nature of these processes are not fully characterized.However, biomechanical and histological assessment could provide aclearer understanding of physiologic tissue changes. Several studieshave been conducted to evaluate biomechanical properties of humanpelvic floor organs [2]. However, studies on freshly harvested humansamples are limited, mainly due to limited access and shortage ofmaterial. Animal models may in part overcome thislimitation.
Objective: The main goal of this study is todocument the effect of multiple deliveries on biomechanical andhistological properties of the ovine pelvic organ tissues, using avirgin sheep model as baseline. The advantage of the sheep model isthat its pelvic floor dimensions and structure are similar to that ofhumans [3]. Sheep also spontaneously develop prolapse in a number ofcases.
Methods: To determine the changes in biomechanicalproperties, pelvic organs from five virgin (mean weight: 46.00 ±1.00 kg, mean age: 11.00 ± 0.316 month) and five parous (after threedeliveries, mean weight: 60.00 ± 1.00 kg, mean age: 4 years ± 0.822month) Swifter sheep were harvested. Samples for uniaxial tensiontest were cut out from the freshly harvested tissues (vagina(distal), bladder, rectum, and uterus) with a punch in longitudinalaxis. Outcome measurements, describing the mechanical properties ofthe native tissue, were obtained from the stress-strain curve. Forhistological analysis, samples were stained with Miller's Elasticastaining to allow identification and quantification of individualstructures (collagen, elastin, smooth muscle content). Collagen,elastin, and smooth muscle fraction area were measured using ImageJprogram. Statistical analysis was performed in order to studypossible variations of pelvic organ tissues between virgin and paroussheep.
Results: No significant differences in mechanicalproperties of vagina and bladder of the virgin and parous sheep werefound (Table 1). However, vaginal wall tissue of virgin sheep wasstiffer than parous. Bladder and rectum of parous sheep were stifferthan of virgin. Significant difference was observed in the uterus;virgin sheep uterus was stiffer than parous (p<0.0001).Histological analysis agreed with the mechanical properties measured.Virgin sheep vagina and uterus were stiffer and contained morecollagen. Parous sheep bladder and rectum were stiffer; therefore,more collagen was expected and observed accordingly (Figure 1).Virgin sheep vagina, bladder and rectum were more compliant andcontained more elastin and smooth muscle. Parous sheep uterus wasmore compliant (p=0.0017), thicker (p <0.0001) and contained moreelastin (p=0.0489), and smooth muscle (p=0.0312).
Conclusions:A detailed comparative analysis of the biomechanical and histologicalproperties of pelvic organs tissues of both virgin and parous sheepwas performed. In this study, it was observed the impact ofrepetitive deliveries on the mechanical properties of pelvic organstissues; it was found that they do not recover to the originallevels. In addition, it was observed that elastin has a significantinfluence on the compliance of soft tissues and collagen is the maincontributor to strength. The histological analysis performed in thisstudy is in line with the mechanical behavior observed.
References:[1] Am J Obstet Gynecol, pp. 175:10-7, 1996.
[2] IntUrogynecol J, Vol. 25, p. 1547-1553, 2014
[3] PLoS One.Vol. 22, p. 9(8), 2014


Biomechanicalproperties of ovine pelvic floor organ tissues


Tissue

Young’smodulus at comfort zone (MPa)

Pvalue

Young’smodulus at stress zone (MPa)

Pvalue

Inflectionpoint

Pvalue

Strainat Ultimate stress

Pvalue

UltimateStrength (MPa)

Pvalue

Vagina

Virgin(5)

2.629
±0.528

0,5676

10.58± 2.575

0,7912

0.129± 0.014

0,5867

0.328± 0.017

0,3857

2.704± 0.239

0,1449

Parous(5)

2.000± 0.529

9.738± 1.697

0.118± 0.014

0.296± 0.030

2.111± 0.342

Bladder

Virgin(5)

0.034± 0.007

0,9184

0.218± 0.028

0,2029

0.575± 0.069

0,2586

1.783± 0.117

0,3183

0.132± 0.012

0,0838

Parous(5)

0.029± 0.009

0.138± 0.012

0.681± 0.052

1.727± 0.096

0.155± 0.026

Rectum

Virgin(5)

0.041± 0.004

0,0834

0.204± 0.019

0,0056**

0.940± 0.056

0,1451

1.497± 0.127

0,8627

0.201± 0.027

0,0473*

Parous(5)

0.056± 0.006

0.292± 0.022

0.841± 0.039

1.474± 0.062

0.254± 0.015

Uterus

Virgin(5)

0.379± 0.0262

<0.0001***

1.704± 0.129

<0.0001***

0.159± 0.012

0,0002***

0.366± 0.0151

0,0017**

0.441± 0.027

<0.0001***

Parous(5)

0.105± 0.0125

0.760± 0.097

0.294± 0.029

0.563± 0.05

0.288± 0.038