Maturation Fetus Ascending Aorta Elastic Properties: Circumferential Strain and Longitudinal Strain by Velocity Vector Imaging.

Xin Zhong,Minghui Liu,Dan Zhou,Yuanchen Luo,Ran Xu,Jiawei Zhou,Shi Zeng

doi:10.3389/fcvm.2022.840494

Abstract

ObjectiveThis study aimed to assess the circumferential and longitudinal strain of the fetal ascending aortic (AA) wall and establish a gestational age-associated longitudinal reference for aortic wall strain during the second half of pregnancy.MethodsSingleton fetuses with gestational age (GA) at 20 + 0 to 24 + 6 weeks were prospectively collected from a low-risk population. Global circumferential strain (GCS) and mean longitudinal strain (MLS) of the ascending aorta were measured serially at 4-week intervals using the velocity vector imaging (VVI) technique. Fractional polynomials were conducted to obtain the best-fitting curves between GA and AA strains. GA-specific reference percentiles of GCS and MLS were established by multilevel modeling.ResultsA total of 223 fetuses with a total of 1,127 serial observations were enrolled. GCS presented a second-degree fractional polynomial smoothing regression along GA (R2 = 0.635, P < 0.05). Fetal aortic GCS remained unchanged at ~27.29% (20.36–35.6%) before 31 weeks and increased significantly from 31.36% (26.38–37.12%) at 31 weeks to 43.29% (30.5–56.78%) at term. MLS presented a third-degree fractional polynomial smoothing regression along GA (R2 = 0.465, P < 0.05). MLS remained steady at ~10.03% (3.28–17.62%) between 20 and 31 weeks and then increased significantly from 12.68% (7.42–20.1%) at 32 weeks to 17.5% (9.67–25.34%) at term. The GCS was significantly higher than the MLS in the ascending aorta wall (p < 0.001).ConclusionThe fetal ascending aorta wall demonstrates obviously greater circumferential strain than longitudinal strain. Both strains remained steady before the late trimester and then gradually increased until delivery, suggesting progressive maturation of aortic elasticity mechanics.

Highlights

The elastic lamella, consisting of elastic fibers interspersed with vascular smooth muscle cells (SMCs), provides the essential elastic properties of the aortic wall, which allow the aorta to reversibly stretch and recoil [2]
The assessment of fetal Ascending aortic (AA) strain was attempted in 238 singleton fetuses
Fetal aortic Global circumferential strain (GCS) remained unchanged at ∼27.29% (20.36–35.6%) before 31 weeks and increased significantly from 31.36% (26.38–37.12%) at 31 weeks to 43.29% (30.5–56.78%) at term (p < 0.001)

Summary

Introduction

The aorta is a conduit to carry blood away from the heart to the peripheral arteries It exhibits an impedance matching function [1]: it can expand in systole after absorbing most of the left ventricular contraction energy and recoil during diastole to guarantee continuous blood flow throughout the cardiac cycle. The elastic lamella, consisting of elastic fibers interspersed with vascular smooth muscle cells (SMCs), provides the essential elastic properties of the aortic wall, which allow the aorta to reversibly stretch and recoil [2]. They are formed within a narrow time during humans’ lifespan beginning in mid-gestation, maximum accumulation in the perinatal period, further rapid decline, and ending in adolescence [3–6]. These parameters cannot directly evaluate the mechanical elastic properties of the aortic wall under cyclic stress and pressure

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