Computational Modelling of Arterial Wall Dynamics and Hemodynamics for Simulation of Early Vascular Ageing

Clinical Background: The elastic nature of blood vessel walls is an evolutionary adaptation that ensures the smooth transition of the pulsatile blood flow generated by the heart into a steady flow essential at the cellular level. This cushioning function of the larger arteries in our body is primarily composed of two components: (a) a structural stiffness component, determined by the relative composition of elastin and collagen fibers in the medial layer of the vessel wall, which imparts a pressure-dependent hyperelastic property, and (b) a functional stiffness component, determined by the response of smooth muscle cells to endothelial stimulation and autonomic nervous system control, which dynamically adjusts vascular tone to enable the body to adapt the vessel wall's elasticity to meet varied physiological demands.

Structural stiffness changes occur gradually over the years, leading to increased vascular stiffness and subsequently elevated blood pressure, while impaired functional stiffness often accompanies—and even precedes—structural stiffness. Both components are early indicators of vascular dysfunction

therefore, a reliable, accurate, and non-invasive assessment can detect subclinical vascular disease years before conventional risk markers (blood pressure, blood sugar, lipid profile, etc.) get deranged.

However, accurate assessment of these non-linear, pressure-dependent material properties using non-invasive methods requires the simultaneous acquisition of transmural pressure, blood flow velocities, and arterial distention waveforms, which is feasible only in research settings. Moreover, the pressure dependency of intrinsic material properties complicates the measurement, as each individual's blood pressure will be different and varies at the time of measurement, preventing a standardized estimation of these properties. Therefore, it is imperative to develop novel methods for performing reliable, non-invasive assessments of the intrinsic material properties of vessel walls at standardized or controlled ranges of transmural blood pressures.

Proposed Work: In this project, we propose to set up a computational fluid-structure interaction (FSI) model of the large arteries (aorta and carotid artery) to study vessel wall dynamics and hemodynamics. The arterial wall will be modeled as a heterogeneous, multilayered structure with non-linear, hyperelastic material properties that emulate the transmural pressure-dependent incremental elastic modulus behavior observed in real arteries. We will model the pulsatile blood flow and simulate pulse wave propagation through a hyperelastic arterial wall to examine the effect of varying transmural pressure on the local pulse wave velocity estimated across an arterial section. Additionally, we will simulate the incremental pulse wave velocity phenomenon, which results in higher pulse propagation velocities near the systole phase of the cardiac cycle, a consequence of the hyperelastic wall properties.

Furthermore, we will emulate accelerated/early vascular aging (EVA) and subclinical vascular disease by modeling various elastin-collagen ratios within the vessel wall structure, altering the hyperelastic stress-strain relationship of the wall material. We will study the effects of EVA on vessel wall and hemodynamic parameters, such as wall motion patterns, distension waveforms, local pulse wave velocity, pulse contour markers, and reflected wave transit time, estimated from both the pressure pulse wave and arterial distension pulse waveform.

The FSI model developed in this project will serve as a ground-truth generator, simulating non-invasively measurable diameter, pressure, and flow waveform shapes under various disease conditions. This research will thus enable the development of novel, non-invasive sensing methods for the reliable assessment of blood vessel wall material property changes A/Prof.d with aging and disease.

Computational modelling and simulation would be performed at Deakin University, while experimental verification of the models using arterial flow phantoms and excised bovine artery samples excited using physiological flow pumps, along with invasively measured pressure and flow waveforms, would be performed at Advanced Cardiovascular Technologies (ACT) Lab at IIT Madras.