Computational model of the fetal cardiovascular system with aortic coarctation

Tutors: Bart Bijnens, Inma Villanueva. Treball de fi de grau en BiomèdicaAortic coarctation (AoC) is a challenging congenital heart disease (CHD) to diagnose prenatally, accounting for 6-8% of all CHDs. It involves the narrowing of a segment of the aortic arch, typically affecting the aortic isthmus. Prenatal diagnosis of AoC is difficult due to the presence of the fetal shunt called ductus arteriosus (DA), which bypasses the defect in fetal circulation. During fetal life, the body adapts to coarctation by establishing mechanisms for adequate oxygen and nutrient delivery as well as pressure regulation to prevent adverse remodelling. However, following birth, a multitude of hemodynamic effects can arise as a result of ductal closure. The primary indicator of AoC is ventricular disproportion, characterized by left-to-right blood flow redistribution resulting in an imbalance with dominant right ventricles. Nonetheless, false-positive diagnoses can occur due to physiological right dominance in the third trimester. The lack of clear prenatal diagnosis criteria for AoC arises from the inconsistency of associated signs. Thus, achieving an accurate prenatal diagnosis of AoC continues to pose a significant challenge. Given the above, this study aimed to develop a closed 0D computational model of the fetal cardiovascular system to improve the understanding of AoC. Particularly, it aimed to simulate the hemodynamic changes in the fetal circulation considering different scenarios of AoC. To that end, we used a closed 0D model that was further extended in order to add more detail and obtain a circuit more consistent with the real anatomical configuration of the fetal system. Then, a thorough parametric analysis was carried out to adjust the parameters of the extended lumped circuit and replicate the behavior of a healthy fetus described in the literature. Finally, multiple scenarios of aortic coaction were simulated considering different degrees of narrowing, ventricular disproportion and increment in the radius of the DA. The obtained results demonstrate the capacity of the extended closed 0D lumped circuit to mimic the hemodynamic behavior of a healthy fetus. Moreover, it has been found that, in the context of AoC, it is imperative for the body to combine the narrowing of aortic segments and the ventricular disproportion, to ensure proper blood delivery, regulate wall stress and wall shear stress in the upper body and most importantly, the brain and the left ventricle. Thus, this study has identified the specific conditions under which physiological ranges are achieved in the context of AoC. Finally, it has been demonstrated that while DA plays a crucial role in blood flow redistribution toward the lower body, it does not experience any increase in its radius