Ovine multiparity is associated with diminished vaginal muscularis, increased elastic fibres and vaginal wall weakness: implication for pelvic organ prolapse

Stuart Emmerson,Jacinta White,Natharnia Young,Aditya V Vashi,Jerome A Werkmeister,Miranda Davies-Tuck,Anna Rosamilia,John Arkwright,Sharon L Edwards,Kirstin Elgass,Caroline E Gargett,Camden Lo,Luke Parkinson

doi:10.1038/srep45709

Abstract

Pelvic Organ Prolapse (POP) is a major clinical burden affecting 25% of women, with vaginal delivery a major contributing factor. We hypothesised that increasing parity weakens the vagina by altering the extracellular matrix proteins and smooth muscle thereby leading to POP vulnerability. We used a modified POP-quantification (POP-Q) system and a novel pressure sensor to measure vaginal wall weakness in nulliparous, primiparous and multiparous ewes. These measurements were correlated with histological, biochemical and biomechanical properties of the ovine vagina. Primiparous and multiparous ewes had greater displacement of vaginal tissue compared to nulliparous at points Aa, Ap and Ba and lower pressure sensor measurements at points equivalent to Ap and Ba. Vaginal wall muscularis of multiparous ewes was thinner than nulliparous and had greater elastic fibre content. Collagen content was lower in primiparous than nulliparous ewes, but collagen organisation did not differ. Biomechanically, multiparous vaginal tissue was weaker and less stiff than nulliparous. Parity had a significant impact on the structure and function of the ovine vaginal wall, as the multiparous vaginal wall was weaker and had a thinner muscularis than nulliparous ewes. This correlated with “POP-Q” and pressure sensor measurements showing greater tissue laxity in multiparous compared to nulliparous ewes.

Highlights

To detect changes in vaginal wall pressures along the length of the anterior and posterior walls to better diagnose weakened regions that might be associated with POP15
Ovine vaginal wall displacement or tissue laxity was measured using a modified human POP-Q32 to provide a clinical measure of vaginal wall weakness[18]
Ovine vaginal wall weakness was measured with a novel pressure sensor device[15], which has eight fibre optic pressure sensors inserted 10 mm apart on each of the anterior and posterior blades of a modified speculum that enables the measurement of distributed pressure along both the posterior and anterior vaginal wall (Fig. 1B)

Summary

Introduction

To detect changes in vaginal wall pressures along the length of the anterior and posterior walls to better diagnose weakened regions that might be associated with POP15. The purpose of this study was (1) to analyse “POP-Q” and pressure sensor measurement differences in ovine vagina and (2) to correlate these data with the collagen, elastic fibre and smooth muscle content and biomechanical properties of ovine vaginal tissue to determine if a relationship exists between ECM and smooth muscle content of the vagina, its biomechanical properties and susceptibility to POP by parity. We hypothesised that with increasing parity, ECM proteins and smooth muscle content decreases and is associated with altered biomechanical properties of ovine vaginal tissue. These altered properties will relate to vaginal tissue weakness, reflected in abnormal “POP-Q” measurements and changes in pressure distribution along the ovine vaginal wall

Objectives

Results

Conclusion