Numeričko rešavanje odnosa pravog i lažnog lumena akutne aortne disekcije

Abstract

Aorta, kao osnovni i najveći krvni sud u čoveku, neprekidno je izložena visokom pulzativnom pritisku i smičućim silama. Disekcija aorte predstavlja veoma ozbiljno i urgentno stanje, u kojem dolazi do cepanja i raslojavanja unutrašnjeg sloja aortnog zida, dok spoljnji sloj ostaje netaknut. Numeričke simulacije dinamičkog ponašanja fluida-krvi u aorti sa disekcijom mogu dosta pomoći lekarima, jer daju uvid u dalji razvoj bolesti. Osnovni metod koji je korišćen u ovom radu jeste metod konačnih elemenata (MKE). Brzine strujanja fluida, pritisaka i smičućih napona u čvorovima konačnih elemenata određuju se u karakterističnim tačkama pulzatornog strujanja krvi. U jednom delu rada, primenom komercijalnih softvera, izvršene su trodimenzionalne rekonstrukcije medicinskih snimaka, a potom, primenom softvera koji je razvijen u Istraživačko razvojnom centru za bioinženjering, sprovedeno je numeričko rešavanje odnosa pravog i lažnog lumena akutne aortne disekcije. Osnovni cilj teze je da se primenom numeričkih simulacija odrede pritisci, smičući naponi i brzine u pravom i lažnom lumenu čime se dobija jasna slika njihovog međusobnog odnosa. Virtuelnim simuliranjem efekta operacije (isecanjem uzlazne aorte i zamene tubus graftom) određuju se protoci kroz bočne opstruirane grane aorte zahvaćene disekcijom, što pokazuje kako hirurški zahvat zamene uzlazne aorte i prekidanje protoka lažnog lumena, ima uticaj na protok kroz grane aortnog luka i visceralne grane (grane abdominalne aorte). Određivanjem von Mizesovih napona u zidu lažnog lumena dobijaju se potencijalna mesta rupture aorte. Ovim putem se neinvazivnim pristupom određuje rizik od nastanka rupture aorte i daje prednost ovom metodu, umesto kriterijuma maksimalnog prečnika.

Aorta, as the main and the largest blood vessel in the human body, is constantly exposed to high pulse pressure and shear forces. Aortic dissection is a very serious condition and medical emergency, which leads to tearing and delamination of the inner layer of the aortic wall, while the outer layer remains intact. Numerical simulations of the dynamic behavior of fluid-blood in the aorta dissection can be of great help to doctors, because they provide insight into further development of the disease. The main method used in this paper is the finite element method (FEM). Fluid velocity, pressure and wall shear stress in nodes of finite elements are determined by specific points of the pulsatile blood flow. One section of the paper focuses on a three-dimensional reconstruction of medical images using a commercial software and in the next section, by using the software developed in the Research and Development Centre for Bioengineering, the numerical solution of relations between true and false lumens of acute aortic dissection is performed. The main objective of the thesis is to determine pressures, wall shear stress and velocity in the true and false lumen by applying numerical simulations, which gives a clear picture of their relationship. Virtual simulation of the effects of the operation (by cutting the ascending aorta and replacing it with the stent graft) determines the flow through the obstructed side branches of aortic dissection, which shows how the surgical intervention of replacing the ascending aorta and interrupting the flow in the false lumen has an impact on the flow through the branches of the aortic arch and the visceral branches (branches of the abdominal aorta). By determining von Mises stresses in the wall of the false lumen, potential points of rupture of the aorta are obtained. In this manner, the risk of rupture of the aorta is determined by using a non-invasive approach, giving this method an advantage over the maximum diameter criterion.