Numerical simulation of pulsatile turbulent flow in tapering stenosed arteries

The Resulting Effect of Flow Pulsations on Calibration Constant of Acoustic Path in Ultrasonic Flowmeters

The present paper compares, for the first time, the regimes of a pulsating turbulent flow in a smooth pipe in terms of 0.001 ≤ ω⁺ ≤ 0.0346 and 0.16 ≤ β ≤ 0.63 at Re ≈ 7000 with the uncertainty in estimating the flow rate by an ultrasonic flowmeter. It was revealed that the classification of pulsating flow regimes according to the dimensionless angular frequency ω⁺ does not have a direct relation with the K parameter equal to the ratio of the phase-average calibration constant in pulsating flow to the corresponding value in steady flow. The results of data processing showed that K depends on the relative amplitude of pulsations β and the position of the chord of the ultrasonic beam trajectory (L/R is distance L from the pipe center to the chord to the pipe radius R). In the coordinates β and L/R, there is a rather wide area where the uncertainty in flow rate estimation of pulsating flows should not exceed 0.5%. An increase in β or L/R leads to an increase in measurement uncertainty, which in the limiting case β, L/R → 1 can reach 5% or more. Favorable and unfavorable areas of the pipe section were identified when scanning pulsating flows and the effectiveness of using multi-path scanning schemes was estimated to reduce the resulting effect of flow pulsations on flow measurement uncertainty.

Elevated electrochemical impedance in the endoluminal regions with high shear stress: implication for assessing lipid-rich atherosclerotic lesions

BACKGROUND

Identifying metabolically active atherosclerotic lesions remains an unmet clinical challenge during coronary intervention. Electrochemical impedance (EIS) increased in response to oxidized low density lipoprotein (oxLDL)-laden lesions. We hereby assessed whether integrating EIS with intravascular ultrasound (IVUS) and shear stress (ISS) provided a new strategy to assess oxLDL-laden lesions in the fat-fed New Zealand White (NZW) rabbits.

METHODS AND RESULTS

A micro-heat transfer sensor was deployed to acquire the ISS profiles at baseline and post high-fat diet (HD) in the NZW rabbits (n=8). After 9 weeks of HD, serum oxLDL levels (mg/dL) increased by 140 fold, accompanied by a 1.5-fold increase in kinematic viscosity (cP) in the HD group. Time-averaged ISS (ISSave) in the thoracic aorta also increased in the HD group (baseline: 17.61±0.24 vs. 9 weeks: 25.22±0.95dyne/cm(2), n=4), but remained unchanged in the normal diet group (baseline: 22.85±0.53dyn/cm(2) vs. 9 weeks: 22.37±0.57dyne/cm(2), n=4). High-frequency intravascular ultrasound (IVUS) revealed atherosclerotic lesions in the regions with augmented ISSave, and concentric bipolar microelectrodes demonstrated elevated EIS signals, which were correlated with prominent anti-oxLDL immuno-staining (oxLDL-free regions: 497±55Ω, n=8 vs. oxLDL-rich lesions: 679±125Ω, n=12, P<0.05). The equivalent circuit model for tissue resistance between the lesion-free and ox-LDL-rich lesions further validated the experimental EIS signals.

CONCLUSIONS

By applying electrochemical impedance in conjunction with shear stress and high-frequency ultrasound sensors, we provided a new strategy to identify oxLDL-laden lesions. The study demonstrated the feasibility of integrating EIS, ISS, and IVUS for a catheter-based approach to assess mechanically unstable plaque.

Large eddy simulation of a stenosed artery using a femoral artery pulsatile flow profile

Computational fluid dynamics simulation of stenosed arteries allows the analysis of quantities including wall shear stress, velocity, and pressure; detailed in vivo measurement is difficult yet the analysis of the fluid dynamics related to stenosis is important in understanding the likely causes and ongoing effects on the integrity of the vessel. In this study, a three-dimensional Large Eddy Simulation is conducted of a 50% occluded vessel, with a typical femoral artery profile used as the transient inlet conditions. The fluid is assumed to be homogenous, Newtonian and incompressible and the walls are assumed rigid. The stenosis is axisymmetric, however the three-dimensional study allows for a flow field that is not axisymmetric and results show significant three-dimensionality. High values of wall shear stress and oscillatory values of wall shear stress (varying in both space time) are observed. The results of the study give insight into the time-varying flow structures for a mildly stenosed artery and indicate that three-dimensional simulations may be important to gain a complete understanding of the flow field.