Identification of biomechanical properties in vivo in human uterine cervix

Abstract

Background and aims: The course and outcome of pregnancy is closely correlated to change of biomechanical properties of the uterine cervix. The aim of this study was to build a non-linear, fiber reinforced mechanical model of the cervix for estimation of mechanical characteristics of the cervix in early- and term-pregnant women based on recordings of in vivo pressure and diameter by means of the Functional Luminal Imaging Probe (FLIP) technology.

Materials and methods: Five early- and six term-pregnant women were examined with a FLIP probe. The bag on the probe was inserted into the cervical canal for concomitant measurement of diameters at 16 serial locations along the canal and the bag pressure. The bag was inflated to a maximum volume of 50 ml. A three-fiber-families model including isotropic elastin-dominated matrix and anisotropic collagen was introduced to describe the mechanical behavior of the cervical canal. The unknown geometric and mechanical parameters were calculated on the basis of the mid-cervical diameters and the intraluminal pressures during the inflation.

Results: The wall thickness in the unloaded state (zero pressure applied) and mechanical properties of the matrix material (c) and collagens (c1, c2) were estimated with good fits of the calculated intraluminal pressures to the FLIP recordings during the cervical canal distension. No significant difference in the wall thickness was found between the early- and term-pregnant women (10.3 ± 0.8mm vs. 11.7 ± 2.2mm, p=0.30). The cervical matrix material and the collagen in the early-pregnant women were much stiffer than that in the term-pregnant women (p<0.05).

Conclusions: The cervical mechanical properties can be obtained from recorded pressure and diameter data in vivo via the established mechanical model. Matrix material and collagens of the cervix wall were remodeled during pregnancy. The mechanical model can be applied to other tubular visceral organs where concomitant measures of pressure and diameter can be obtained for better understanding diseases and their evolution or treatment.

Keywords: FLIP; In vivo; Mechanical model; Uterine cervix.