Advanced Human Hemodynamic Modelling and Valuation using MRI imaging

Proper functioning of brain critically depends on cerebral blood inflow and outflow. Moreover, the venous contribution in auto-regulation function and maintaining pressure and blood flow balance in body organs such as brain has been highlighted. Auto-regulating mechanism and cerebral circulation are influenced by many biophysical factors such as aging, posture and gravitational pressure change, and vessel stenosis. Therefore, it is important to gain a satisfactory understanding of physiological and biomechanical properties of the venous system and the interaction between intra- and extracranial compartments under different physiological conditions. For what concerns congenital vascular disease is one of the known leading causes of death in paediatric age. Despite the importance of paediatric haemodynamics, large investigations have been devoted to the evaluation of circulation in adults. The novelties of this study consist in the development of a well calibrated mathematical model of cardiovascular circulation in paediatric subjects as well as adults, simulating the full range posture change effects on hemodynamic physiology from head down tilt to supine and upright, predicting the flow rate change in main neck arteries and veins in microgravity environment, and the IJV asymmetric stenosis (followed by head rotation) effects on the head and neck hemodynamic alteration. The model consists of two parts that simulates the arterial (1D) and brain and venous (0D) vascular tree. The cardiovascular system is built as a network of hydraulic resistances and capacitances to properly model physiological parameters like total peripheral resistance, and to calculate vascular pressure and the related flow rate at any branch of the tree. This dissertation presents the results of the scientific work developed in collaboration with the paediatric hospital of Sant Joan de Déu ,Spain. A data set was provided including information about human vessels network anatomy, blood rheology (blood velocity and flow), vessel status, venous biomechanics factors (inner pressure and wall shear stress) and also volunteers characteristics (age, respiratory rate, bloop pressure and clinical reason of their MRI scan). The model presented here was tuned by using two different MRI datasets. We benefited from the use of 2D and 4D PC-MRI techniques. Results show that the model is able to reproduce the physiological behavior of IJVs and other collateral veins, with average values in good agreement with experimental data of supine paediatric and adult subjects. Physiological age-related parameters were used to adjust left ventricle pressure pulse and cerebral blood flow for paediatrics. Every simulated data fell inside the standard error from the corresponding average experimental value. The model outcomes indicated about 88% correlation with MRI data. Concerning the head rotation effects simulation, the conductance of left IJV was decreased to model the imposed stenosis influenced by torsion-compression force. MR image acquisition and numerical simulation were performed in two situations: the neutral and 80 degree left head rotation. Flow rate and wall shear stress analysis within IJVs demonstrated a strong interindividual dependency. Concerning the posture change and microgravity study, the model in line with literature confirmed the role of peripheral veins in regional blood redistribution during posture change from supine to upright and microgravity environment as hypothesized in literature. Therefore, model outcomes are in excellent agreement with experimental average flows and literature. The methods presented can be used to predict the response of the hemodynamic system in many other physiological and pathological conditions in both paediatric and adult cases. It also provides a virtual laboratory to examine the consequence of a wide range of orthostatic stresses on haemodynamics.