Effect of red blood cell concentration on the blood flow in patient-specific aneurysms

Purpose: Because plasma and red blood cells are the predominant components of human blood, their abundance and deficiency can arise serious consequences related to cerebral aneurysms. The effect of variations in the hematocrit level on the blood flow was studied in two cerebral aneurysms. Method: A three-dimensional computational fluid dynamics study being capable of handling multi-phase nature of blood flow was performed to examine the effect of hematocrit variation in two patient-specific aneurysms. The Euler–Euler method and the Carreau–Yasuda viscosity models were used for the simulations. Blood inflow jet penetration depth, flow patterns in the impingement zone, complexity of flow in the aneurysm sac region and wall shear stress-based parameters are investigated at different hematocrit levels. Results: The results showed that the maximum inflow jet penetration was achieved at the lowest hematocrit level. This was accompanied with strong flow impingements at the narrow corners deep inside the aneurysm sac and undesired complex flow patterns extending from the entrance to the aneurysm dome. Conclusions: The decrease in hematocrit level changed the characteristics of the velocity profile inside the dome from a single- to a double-peak distribution, which increased the likelihood of a daughter aneurysm formation. Furthermore, the time averaged wall shear stress and oscillatory shear index indicators showed that lowering the hematocrit values could change an initially low-risk case into a very high rupture risk situation.