Computational fluid dynamics (CFD) in vascular system dynamics and blood flows

Vascular diseases are the diseases related to the circulatory system in human, which is blamed for the deaths of millions every year.

Despite incredible progress made in the past decades in understanding the causes of these diseases and hence their treatment, the medical science still suffers from the lack of fundamental understanding of the root of the creation and development of these diseases. Biomedical Engineering (BE) is a branch of engineering which experimentally and numerically deals with studying medical problems either related to the living parts or medical devices. One of the most interesting applications of BE is associated with the computational modeling in the vascular system though the state-of-the-art methods in the modeling face real challenges for accurate predictions for biological systems as one can expect for ordinary materials.

Our group has been involved in CFD modeling of species transport and blood flow in arteries since 2005. Dr. Mahsa Dabagh is the first graduated doctor (2008) from our group who is now the primary researcher and supervisor of our doctoral students. Dr. Paritosh Vasava graduated in Dec. 2011 is our expert in the reconstruction of arteries from CT images and transferring them into proper CAD format for simulations in FLUENT. M.Sc. Zuned Mansuri is currently pursuing his PhD studies to investigate what happens in stented coronary arteries. This work is supported by the Academy of Finland via a 4-years term project (2008-2011) and also the CFD graduate school in Finland.

Starting initially with ideal geometry of aorta, we studied the flow features during pulsatile flow. This study is published in P. Vasava, P. Jalali, M. Dabagh, P.J. Kolari, Computational and Mathematical Methods in Medicine, Vol. 2012, Article ID 861837, 13 pages.

 

Figure 1. Snapshot of flow in the mid cross section of idealized aorta.

 

We have developed fully automatic way to extract the geometry of aorta with all branches (Fig. 2a) from CT scans of abdominal part of body. The resultant geometry is meshed as shown in Fig. 2b and 2c.

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Figure 2. (a) Extracted human aorta from CT scans by fully automatic techniques. (b) Lower and (c) upper views of the meshed geometry of aorta. Responsible students are Paritosh Vasava and Mahmoud Mortazavi.

Pulsatile blood flow is simulated using CFD to obtain the distribution of shear stresses on the wall of aorta (Fig. 3). This figure depicts how the wall shear stress (WSS) distribution changes between two instants in the cardiac cycle. Places with lower WSS are known to be more vulnerable for the development of atherosclerosis. For complete description of the work you can refer to the PhD thesis of Paritosh Vasava.

 

Figure 3. Distribution of WSS in two instants of the cardiac cycle in pulsatile flow. Responsible student is Paritosh Vasava.

 

 

The WSS is one of the important factors that changes the arrangement and correspondingly the function of Endothelial Cells (EC), which cover the innermost layer of all kind of vessels called Endothelium. The low-density lipoprotein (LDL) macromolecules can pass through certain passages (leaky junctions) of endothelium. The penetration of LDL through these passages is investigated by Dr. Mahsa Dabagh (Dabagh et al., American Journal of Physiology: Heart & Circulatory Physiology 297: H983-H996 (2009)).

 


Figure 4. Geometric representation of the model for the local penetration of LDL through its main passage (leaky junction) on endothelium into into and across different layers of arterial wall.

Dr. Mahsa Dabagh also worked (Dabagh et al., Medical Engineering & Physics 31: 816-824 (2009); Dabagh et al., Journal of Porous Media 12(3), 201-212 (2009)) on models of transmural flow across the media layer to understand how the shear stress is distributed on smooth muscle cells (SMCs) which stimulates their migration to the intima layer followed by their transition to foam cells and hardening the intima layer (atherosclerotic plaques).

 

Figure 5. Schematic representation and the computational domain for the simulations of transmural flow across the media layer to find out about the shear stress on the surface of SMCs as a stimulus for their migration to intima.

Full description of this research can be found in the PhD thesis of Mahsa Dabagh.