Determination of hyperelastic properties for umbilical artery in preeclampsia from uniaxial extension tests.

OBJECTIVE: Preeclampsia often results in altered hemodynamics and structurally remodeled umbilical arteries in the fetus--alterations that may be associated with arterial stiffening. We therefore hypothesized that the mechanical function of preeclamptic (PE) umbilical arteries had increased stiffness compared to control. STUDY DESIGN: Umbilical arteries were collected from control (n=9) and PE (n=6) pregnancies without any other complications. Samples were tested uniaxially in axial and circumferential directions for the passive mechanics. The umbilical artery was modeled as a fiber reinforced hyperelastic material in both control and PE conditions. RESULTS: The PE arteries were stiffer than control arteries at stresses of 20-160 mmHg in the axial direction and 65-200 mmHg in the circumferential direction (P<0.05). The PE umbilical arteries exhibited a 58% and 48% increase in circumferential moduli at the systolic and diastolic blood pressure respectively compared to the controls (P<0.05). A hyperelastic model showed a substantial increase in both isotropic and anisotropic contribution in the mechanical behavior. Collectively, the changes observed correlated to a higher collagen fiber density in the PE group with increased hyperelastic material parameters (P<0.05). CONCLUSION: PE umbilical arteries demonstrated stiffer biomechanics compared to the controls due to the change in collagen fiber content. These altered biomechanical and structural changes provide a potential snapshot into systemic vasculature remodeling occurring in the newborn.