D3: Tissue Mechanics

QUANTIFICATION OF WALL SHEAR STRESS IN HUMAN FETAL UMBILICAL VESSELS: AN IN VIVO STUDY


Shier Nee Saw1, Dawn Chia1, Citra Nurfarah Zaini Mattar1,2, Arijit Biswas1,2, Choon Hwai Yap1


1National University of Singapore, Singapore;
2National University Health System, Singapore


Introductions:
It is widely known that endothelial cells (ECs) are highly responsive to shear stress and is important in regulating vascular growth and remodeling. Umbilical vascular ECs are also popular cell sources in mechanobiology studies, but detailed measurements of their native WSS environment is not comprehensively done. Understanding the native environment of umbilical ECs can provide clues for treatment of diseases such as intrauterine growth restriction where flow resistance in the placenta is high. 

Methods:
This study included 28 pregnant women who underwent routine growth scan from 32nd to 33rd week gestational age in NUH, Singapore. Blood velocities were quantified through pulsed- wave Doppler and cross-sectional vascular areas were quantified through 3D reconstruction from 3D B-mode ultrasound images. Poiseuille’s equation was used to compute WSS in umbilical veins (UV) while iterative scheme of Compuutational Fluids Dynamics (CFD) simulations was adopted in computing the WSS in umbilical arteries (UA). Effect of bending of the umbilical cord was also investigated using CFD. 

Results and Discussions:
Ultrasound measurements showed that there is no correlation between blood flow velocities and diameters in both UAs and UV. CFD studies showed that UA’s WSS had negative correlation with its diameter, but it was not statistically significant; UV’s WSS demonstrated a stronger and statistically significant negative correlation with the vessel diameter, suggesting that UV and UA might utilize different cues for vascular remodeling. In a straight vessel like the UV, bending caused elevation of WSS and vascular resistance, but it did not affect the helical-shaped UA much.

Conclusions:
There are essential differences in hemodynamics environments of the UA and UV. UA helical geometry provides a more stable hemodynamics condition compared to straight bend geometry, allowing UA to sense hemodynamics flow rates without being interfered by cord bending. 

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