The effect of non-Newtonian blood flow on the value of wall shear stress (WSS) of an intracranial aneurysm was investigated using computational fluid dynamics. For cerebral arteries, blood is often assumed to behave as a Newtonian fluid, though the effects of non-Newtonian flow on the prediction of areas of low WSS associated with aneurysm rupture are not clear. Geometry was based on published data and a Newtonian model validated against experimental results. Newtonian, unrestricted non-Newtonian, and viscosity-limited non-Newtonian models were compared under pulsatile conditions. Peak WSS of the Newtonian model was 28.7 Pa, and the lowest value of peak WSS for the unrestricted non-Newtonian models was 16.5 Pa. Viscosity-limited non-Newtonian models predicted flow velocity and WSS similar to those predicted by the Newtonian model in high-shear-rate regions, though maximum areas of critically low WSS were up to 42 % smaller than those predicted by the Newtonian model. In conclusion, viscosity limits are required to prevent excessive thinning of non-Newtonian models and the effects of non-Newtonian viscosity are significant for blood flow within low-shear-rate regions of an intracranial aneurysm.
BackgroundPrevious studies have found that increasing plasma viscosity as whole blood viscosity decrease has beneficial effects in microvascular hemodynamics. As the heart couples with systemic vascular network, changes in plasma and blood viscosity during hemodilution determine vascular pressure drop and flow rate, which influence cardiac function. This study aimed to investigate how changes in plasma viscosity affect on cardiac function during acute isovolemic hemodilution.Materials and MethodsPlasma viscosity was modulated by hemodilution of 40% of blood volume with three different plasma expanders (PEs). Dextran 2000 kDa (Dx2M, 6.3 cP) and dextran 70 kDa (Dx70, 3.0 cP) were used as high and moderate viscogenic PEs, respectively. Polyethylene glycol conjugated with human serum albumin (PEG-HSA, 2.2 cP) was used as low viscogenic PE. The cardiac function was assessed using a miniaturized pressure-volume conductance catheter.ResultsAfter hemodilution, pressure dropped to 84%, 79%, and 78% of baseline for Dx2M, Dx70 and PEG-HSA, respectively. Cardiac output markedly increased for Dx2M and PEG-HSA. Dx2M significantly produced higher stroke work relative to baseline and compared to Dx70.ConclusionAcute hemodilution with PEG-HSA without increasing plasma viscosity provided beneficial effects on cardiac function compared to Dx70, and similar to those measured with Dx2M. Potentially negative effects of increasing peripheral vascular resistance due to the increase in plasma viscosity were prevented.
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