Department of Civil Engineering, Government Engineering College, Thrissur, Kerala, PIN:680009, India
The performance of the heart is considerably affected by the blocks formed because of the deposition of plaque inside the coronary artery. The blocks (stenosis) either in coronary artery or elsewhere force the heart to work harder for pumping the oxygenated blood to the heart muscles and blood vessels. This study analyses the flow through the stenosed coronary arteries via numerical modelling by using ANSYS FLUENT software. Three real cases with different asymmetric stenosis levels (i.e., block level 33%, 66% & 85%) are analysed by considering blood as a non-Newtonian fluid, and blood flow as pulsatile in nature. As the flow regime falls in transition to turbulent region, the transition Shear Stress Transport (SST) k-ω turbulence model is used to take care of the changeover stage from laminar to turbulent flow and vice versa. The results show large variation both in Wall Shear Stress (WSS) and pressure drop near the stenosis. Pressure drop becomes more significant at severe degrees of stenosis (66% and 85%) compared to the mild case (33%). The study throws light on the critical distribution of shear stress and pressure drop along the artery wall, which are considered as indicators of the commencement of heart disease and further growth of stenosis. An indicator, viz., Fractional Flow Reserve (FFR), which relates the percentage of stenosis to the pressure variations, can be used as an index to diagnose the severity of stenosis. All the three cases with different stenotic levels were analysed under hyperaemic conditions and found that even 45% stenosis case can go near to critical at hyperaemic flow conditions. The effect of severity due to vessel constriction can be estimated by comparing the simulated pressure drop and WSS before and after the stenosis, with the ones for a healthy artery. The present study developed a methodology to calculate FFR value for unknown percentage of stenosis based on the simulated results obtained from 33%, 66% and 85% stenosis. Thus, criticality of a patient with certain percentage stenosis can also be evaluated. This simulation technique can be recommended as a non-invasive diagnostic tool for the early detection of atherosclerosis.