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///2018 Abstract Details
2018 Abstract Details2019-08-02T15:57:01-05:00

Geometric And Hemodynamic Characterization of Uterine Spiral Arteries

Abstract Number: S3A-6
Abstract Type: Original Research

Yehuda Ginosar BSc MBBS1 ; D Michael Nelson MD PhD2; Mair Zamir PhD3

Background: A critical component of the uteroplacental circulation is the spiral artery. During the course of normal pregnancy, "spiral" arteries are transformed into dilated, high-flow, low-pressure vessels, predominantly due to invasion of trophoblasts from the developing placenta, but also due to a reduction in the number of loops per unit length (pitch), as the gravid uterus grows in size. Impaired "spiral" artery transformation is implicated in preeclampsia, intrauterine growth restriction (IUGR) and prematurity. We present a geometric and hemodynamic exploration of the possible role of spiral geometry in these events, in the context of uteroplacental blood flow in pregnancy.

Methods: We examine the effects of curvature by comparing the flow in three vessels penetrating the same depth of tissue: (i) straight, (ii) helical, and (iii) spiral (Fig 1a). We caution that the term "spiral" is often used interchangeably in the literature to mean spiral or helical. We explore both geometric effects of curvature (any deviation from the linear adds to vessel length and hence to resistance) and the centrifugal effects of curvature (where resistance increases because of secondary flow eddies). The latter of these effects is embodied in a variant of the Dean number

D=√(2r/R) ((Gr^3 ρ)/μ^2 )

where r is the radius of the vessel, R is the local radius of curvature of the coil, G is the pressure gradient driving the flow, ρ is blood density, and µ is blood viscosity.

Results: The geometric (length) effect of curvature is more significant than the centrifugal effect in much of the spiral artery. The geometric effect of curvature is lower for the spiral artery than for the helical artery, as the unwound length of vessel is shorter (Fig 1b). The curvature effects are determined by the Dean number, which is zero in the straight artery, and constant (non-zero) in the helical artery. In the spiral artery, the Dean number increases precipitously to the point of becoming (mathematically) infinite as the radius of curvature of the spiral diminishes to zero towards the intervillous space (Fig 1c).

Conclusions: Mathematical modelling of "spiral" artery blood flow may be useful in understanding uteroplacental blood flow in normal and pathological pregnancy.

SOAP 2018