Abstract
BackgroundThis study describes a new method for determining site-specific vascular shear stress using dynamic measures of shear rate and blood viscosity (BV) in the carotid arteries, and examines characteristics of carotid arterial shear stress among patients with lacunar infarction.MethodsVascular shear stress measurements were conducted in 37 patients (17 lacunar infarction patients and 20 control subjects) using duplex ultrasonography. Vessel wall diameters and velocities were measured in each arterial segment at peak-systolic (PS) and end-diastolic (ED) phases, for calculation of PS/ED shear rates. PS/ED shear stresses [dyne/cm2] were determined with PS/ED shear rates and shear-rate dependent BV values. For comparison, both values of hematocrit-derived BV and BV measurements at 300 s-1 were used for calculation of shear stress.ResultsAll cardiovascular disease (CVD) risk factors including BV values were similar between the two groups. In both common carotid arteries, PS and ED shear stresses were significantly lower in the patients with lacunar infarction than in controls in multivariate models that included age, sex, and other major CVD risk factors. PS and ED shear stresses using the shear rate specific BV were 4.5% lower and 7.3% higher than those using the two other BVs, respectively.ConclusionLacunar infarction was associated with reduced carotid arterial shear stress. The use of estimated BV for calculating carotid arterial shear stress provides more accurate assessment of the hemodynamic contribution of shear stress than previous models that have arbitrarily assigned a constant value to this dynamic flow property.
Highlights
This study describes a new method for determining site-specific vascular shear stress using dynamic measures of shear rate and blood viscosity (BV) in the carotid arteries, and examines characteristics of carotid arterial shear stress among patients with lacunar infarction
All the PS and ED shear rates at the both-sided common carotid artery (CCA) were significantly lower in the patients with lacunar infarction than the controls
There was no significant difference of the PS and ED shear stresses at the both CCAs according to the laterality of lacunar infarction
Summary
This study describes a new method for determining site-specific vascular shear stress using dynamic measures of shear rate and blood viscosity (BV) in the carotid arteries, and examines characteristics of carotid arterial shear stress among patients with lacunar infarction. The vascular system can generally be viewed as a closed system, constraining a series of biochemical processes and mechanical stresses that are regulated by various homeostatic mechanisms [1] From this theoretical perspective, if mechanical stresses such as wall shear stresses and tensile stresses are not properly dispersed, an artery may sustain injury. Blood viscosity is higher at low shear rates (γ_ ) and is reduced as shear rate increases [4] This shear rate dependent aspect of blood viscosity (BV, μ) has presented challenges to the accurate calculation of vascular wall shear stress, the frictional force per unit area acting tangentially to the arterial wall. The non-Newtonian characteristics of blood have been assumed in some previous studies, BV over ranges of shear rates have not been measured directly, but the laws of viscosity were applied empirically [9,10]
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