Cerebral circulation | EPFL Graph Search

Cerebral circulation is the movement of blood through a network of cerebral arteries and veins supplying the brain. The rate of cerebral blood flow in an adult human is typically 750 milliliters per minute, or about 15% of cardiac output. Arteries deliver oxygenated blood, glucose and other nutrients to the brain. Veins carry "used or spent" blood back to the heart, to remove carbon dioxide, lactic acid, and other metabolic products. The neurovascular unit regulates cerebral blood flow so that activated neurons can be supplied with energy in the right amount and at the right time. Because the brain would quickly suffer damage from any stoppage in blood supply, the cerebral circulatory system has safeguards including autoregulation of the blood vessels. The failure of these safeguards may result in a stroke. The volume of blood in circulation is called the cerebral blood flow. Sudden intense accelerations change the gravitational forces perceived by bodies and can se

Reduced order models for the simulation of pathological heart valves

Lidia Stepanova

Numerical modeling of the human cardiovascular system (CVS) represents an active branch of research which allows the medical specialists to advance in understanding of underlined processes of blood circulation and the heart work at any scale, moreover, it helps to analyze the potential problems which can arise in the CVS by modifying the parameters inside the mathematical models. Due to inability to capture in details the pressure and flow parameters without invasion into heart chambers, the process of diagnosing heart diseases can become very complicated, the limited data on atrial pressure and cardiogram results can give only overall representation of the heart condition and the exactness of the diagnosis is based mainly on experience of the doctor. Nevertheless, the development of numerical models of CVS helps to get better understanding on processes which can cause particular disease (reverse flow leakage in heart chambers, improper contraction of heart muscles due to infarction of tissue). Mathematical model allows the analysis of all physical values of the system during the heart beat as well as possibility to adjust individual parameters specific to each patient. Therefore, it becomes an efficient tool for doctors to diagnose properly the heart disease, to assign the necessary treatment and surgery, and to predict the effect of implanting cardiac-assist devices.

2013

One dimensional and multiscale models for blood flow circulation

The aim of this work is to provide mathematically sound and computationally effective tools for the numerical simulation of the interaction between fluid and structures as occurring, for instance, in the simulation of the human cardiovascular system. This problem is global, in the sense that local changes can modify the solution far away. From the point of view of computing and modelling this calls for the use of multiscale methods, where simplified models are used to treat the global problem leaving to more accurate models the local description. Moreover it is characterised by the appearance of pressure waves inside the vessels. In large arteries the vessel wall dynamics can be described by a thin elastic membrane model (Navier equation) while the fluid motion can be represented by the Navier-Stokes equations for incompressible Newtonian fluids. Unfortunately, given the high levels of details furnished by this model, its computational complexity is dramatically high. Therefore reduced models have been developed. In particular, one-dimensional models, originally introduced by Euler, seem to be appropriate for the study in the time-space domain of pressure wave propagation induced by the interaction between the fluid and the vessel wall in the arterial tree. These reduced models are obtained after integrating the Navier-Stokes equations over a vessel section, supposed to be circular, and assuming an algebraic wall law to describe the relationship between pressure and wall deformation. They can be used in place of the more complex three dimensional fluid-structure models or in cooperation with them (multiscale approach). The first part of this work deals with one dimensional models. A reduced 1D model taken from literature is presented and analysed. Some extensions of the basic model, in particular with respect to vessel wall law (generalised string model) and more complex geometries (bifurcated and curved arteries), are also considered. Numerical schemes are proposed and some numerical results are presented. In the second part of this thesis we focus on a multiscale model. We consider a 55 arterial tree, described by the 1D model, coupled with lumped parameter models for heart and capillaries. In particular, specific attention has been devoted to the coupling between the left ventricle and the arterial system, whose physiopathological relevance is well known. This mathematical model gives good results in numerical tests and is able to describe the relevant features of the pressure wave propagation and reflections within the arterial system.

EPFL2004

Development of a novel biomaterial for drug delivery

Anu Kodiyan

Gold nanoparticles (GNPs) are promising tools as drug delivery devices. However, upon intravenous injection, they aggregate and are rapidly eliminated from the systemic circulation by macrophages in the reticuloendothelial system, resulting in relatively short blood circulation time. To circumvent this problem, GNPs are typically coated with poly(ethylene) glycol (PEG). This modification significantly enhances the circulation time of the GNPs in vivo as well as the stability of the particles. However, PEG has limited possibilities of functionalization, as they only have free chemical groups available for conjugation to other molecules on their terminal ends. Alternatively, alginate-derived polymers may be good candidates as GNP stabilizing agents as they are biocompatible, have unique gel forming properties and the advantage that they can readily be conjugated to various therapeutic and targeting molecules since they contain numerous free chemical groups. In this project, a protocol for preparing thiolated alginate-derived polymers and for coating them on the surface of GNPs was established. These polymers were first characterized with analytical methods. Furthermore, physical properties of the GNPs coated with these polymers were analyzed. In vitro experiments were performed to examine the interactions between serum proteins and these GNPs, as well as the cell behavior (viability and uptake) in the presence of these GNPs. Finally, in vivo experiments were done to determine the pharmacokinetics and biodistribution of these GNPs. To verify if any toxicity was induced by the GNPs, histology studies were also done. For comparison, PEGylated and unmodified GNPs were analyzed as well. Results indicated that GNPs coated with alginate-derived polymers were uptaken by cells and had increased stability, reduced interactions with serum proteins and longer blood circulation time than unmodified GNPs. Hence, these particles pave the way for improved drug delivery systems.

2011

Development of a novel biomaterial for drug delivery

Anu Kodiyan

2011

One dimensional and multiscale models for blood flow circulation

EPFL2004