Computational study of pulsatile blood flow in prototype vessel geometries of coronary segments

Non-Newtonian Effects of Blood Flow on Hemodynamics in Pulmonary Stenosis: Numerical Simulation

This paper aims to explore the construction of an individualized pulmonary artery stenosis model based on computed tomography (CT) images. The stenosis model is simulated using a porous medium, and the numerical simulation is carried out by computational fluid dynamics (CFD) method to discuss non-Newtonian effects on hemodynamics. The hemodynamic parameters and quantitative pulmonary pressure ratio (QPPR) of the right pulmonary artery stenosis are obtained. The change curves of hemodynamic parameters show that the effects of non-Newtonian fluid are more significant than those of Newtonian fluid. Under the non-Newtonian condition, pressure and velocity drop more and faster when blood flow enters into the stenosis region. There is a high wall shear stress in the stenosis downstream. The margin of error between the QPPR value of the non-Newtonian fluid simulation and the clinical measurement value is not more than 10%. This work provides the evidence that the simulation of non-Newtonian fluid is closer to the reality when a porous medium model is used in a stenosis model. This contributes to assessing the severity of pulmonary stenosis behavior and is essential to guide disease treatment.

Influence of microvascular sutures on shear strain rate in realistic pulsatile flow

Arterial thrombus formation is directly related to the mechanical shear experienced by platelets within flow. High shear strain rates (SSRs) and large shear gradients cause platelet activation, aggregation and production of thrombus. This study, for the first time, investigates the influence of pulsatile flow on local haemodynamics within sutured microarterial anastomoses. We measured physiological arterial waveform velocities experimentally using Doppler ultrasound velocimetry, and a representative example was applied to a realistic sutured microarterial geometry. Computational geometries were created using measurements taken from sutured chicken femoral arteries. Arterial SSRs were predicted using computational fluid dynamics (CFD) software, to indicate the potential for platelet activation, deposition and thrombus formation. Predictions of steady and sinusoidal inputs were compared to analyse whether the addition of physiological pulse characteristics affects local intravascular flow characteristics. Simulations were designed to evaluate flow in pristine and hand-sutured microarterial anastomoses, each with a steady-state and sinusoidal pulse component. The presence of sutures increased SSR_max in the anastomotic region by factors of 2.1 and 2.3 in steady-state and pulsatile flows respectively, when compared to a pristine vessel. SSR values seen in these simulations are analogous to the presence of moderate arterial stenosis. Steady-state simulations, driven by a constant inflow velocity equal to the peak systolic velocity (PSV) of the measured pulsatile flow, underestimated SSRs by ∼ 9% in pristine, and ∼ 19% in sutured vessels compared with a realistic pulse. Sinusoidal flows, with equivalent frequency and amplitude to a measured arterial waveform, represent a slight improvement on steady-state simulations, but still SSRs are underestimated by 1-2%. We recommend using a measured arterial waveform, of the form presented here, for simulating pulsatile flows in vessels of this nature. Under realistic pulsatile flow, shear gradients across microvascular sutures are high, of the order ∼ 7.9 × 10⁶ m^-1 s^-1, which may also be associated with activation of platelets and formation of aggregates.

A NEW METHOD TO STUDY ATHEROSCLEROSIS AND ASSESS THE EFFECTIVENESS OF PERCUTANEOUS CORONARY INTERVENTION BY COMPUTATIONAL FLUID DYNAMICS SIMULATION

High-pitch spiral computed tomography coronary angiography (CTCA) is able to perform a whole-heart scan within one heartbeat, resulting in high-quality images with high spatial and temporal resolution. To investigate the performance of high-quality CTCA images, an anatomic stenosis evaluation by digital subtracted angiography (DSA) was compared to a functional stenosis evaluation by CTCA-derived fraction flow reserve (FFR). A total of 54 arterial segments with stenosis were collected from 23 patients, and three-dimensional (3D) geometrical models were reconstructed. The computational fluid dynamics (CFDs) analysis was used to calculate the pressure distributions and FFR values. The correlation between anatomic and functional evaluation factors was assessed with either the ratio of anatomic reduction or CTCA-derived FFR values at the corresponding anatomic locations. Pearson correlation analysis was performed, and a significant correlation was found relating to the diameter ([Formula: see text]) and the cross-sectional area ([Formula: see text]). A significant correlation was also found in the functional evaluation relating to the diameter ([Formula: see text]) and the cross-sectional area ([Formula: see text]). High-quality CT images greatly reduce the time needed for geometric reconstruction. Significant advances in the accuracy of the reconstruction have resulted in more accurate CFD analysis, which can help to improve clinical diagnoses. The results of this study show that the CFD method can be a feasible tool for the clinic diagnosis of stenosis and for determining whether a patient requires percutaneous coronary intervention (PCI).

Non-Newtonian Blood Flow Simulation of Diastolic Phase in Bileaflet Mechanical Heart Valve Implanted in a Realistic Aortic Root Containing Coronary Arteries

Coronary arteries, which are branched from the sinuses, have tangible effects on the hemodynamic performance of the bileaflet mechanical heart valve (BMHV), especially in the diastolic phase. To better understand this issue, a computer model of ascending aorta including realistic sinus shapes and coronary arteries has been generated in this study in order to investigate the BMHV performance during diastole. Three-dimensional transient numerical analysis is conducted to simulate the diastolic blood flow through the hinges and in coronary arteries under the assumption of non-Newtonian behavior. Results indicate that as blood flows to the coronary arteries mainly during diastole, leakage flow from the hinge and other gaps will change considering the influence of coronary arteries. In addition, BMHV in the case of aortic replacement will increase blood flow rate into the coronary arteries about 100% as the mechanical valve resistance is higher than a native heart valve. Also, it will change the wall shear stress (WSS) distribution and increase coronary artery disease (CAD) potential. It is found out that although less leakage flow reduces the velocity magnitudes through the gaps, the shear stress acting on blood elements with non-Newtonian assumption will be detrimental in the hinge corner at the ventricular side. High WSS of 1800 Pa is observed at beginning of diastole at this region.

High shear stress induces atherosclerotic vulnerable plaque formation through angiogenesis

Rupture of atherosclerotic plaques causing thrombosis is the main cause of acute coronary syndrome and ischemic strokes. Inhibition of thrombosis is one of the important tasks developing biomedical materials such as intravascular stents and vascular grafts. Shear stress (SS) influences the formation and development of atherosclerosis. The current review focuses on the vulnerable plaques observed in the high shear stress (HSS) regions, which localizes at the proximal region of the plaque intruding into the lumen. The vascular outward remodelling occurs in the HSS region for vascular compensation and that angiogenesis is a critical factor for HSS which induces atherosclerotic vulnerable plaque formation. These results greatly challenge the established belief that low shear stress is important for expansive remodelling, which provides a new perspective for preventing the transition of stable plaques to high-risk atherosclerotic lesions.

Ivabradine: potential clinical applications in critically ill patients

It has been extensively demonstrated that an elevated heart rate is a modifiable, independent risk factor for cardiovascular events. A high heart rate increases myocardial oxygen consumption and reduces diastolic perfusion time. It can also increase ventricular diastolic pressures and induce ventricular arrhythmias. Critical care patients are prone to develop a stress induced cardiac impairment and consequently an increase in sympathetic tone. This in turn increases heart rate. In this setting, however, heart rate lowering might be difficult because the effects of inotropic drugs could be hindered by heart rate reducing drugs like beta-blockers. Ivabradine is a new selective antagonist of funny channels. It lowers heart rate, reducing the diastolic depolarization slope. Moreover, ivabradine is not active on sympathetic pathways, thus avoiding any interference with inotropic amines. We reviewed the literature available regarding heart rate control in critical care patients, focusing our interest on the use of ivabradine to assess the potential benefits of the drug in this particular setting.

Heart rate: a forgotten link in coronary artery disease?

A considerable body of evidence indicates that elevated resting heart rate is an independent, modifiable risk factor for cardiovascular events and mortality in patients with coronary artery disease. Elevated heart rate can produce adverse effects in several ways. Firstly, myocardial oxygen consumption is increased at high heart rates, but the time available for myocardial perfusion is reduced, increasing the likelihood of myocardial ischemia. Secondly, exposure of the large elastic arteries to cyclical stretch is increased at high heart rates. This effect can increase the rate at which components of the arterial wall deteriorate. Elastin fibers, which have an extremely slow rate of turnover in adult life, might be particularly vulnerable. Thirdly, elevated heart rate can predispose the myocardium to arrhythmias, and favor the development and progression of coronary atherosclerosis, by adversely affecting the balance between systolic and diastolic flow. Comparisons of the effects of the specific heart-rate-lowering drug ivabradine with those of β-blockers could help clarify the pathophysiological effects of elevated heart rate. Effective heart rate control among patients with coronary artery disease is uncommon in clinical practice, representing a missed therapeutic opportunity.

Physical and occupational therapy for children with rheumatic diseases

Total management of rheumatic disorders of children includes antiinflammatory drugs, active therapy, maintenance of ADLs, and attention to the psychosocial development of the child. This article focuses on the role that physical and occupational therapists play in the management of children with arthritis. The complexity of the problems of these children necessitates a multidisciplinary team approach, with professionals who are committed to helping the child lead as normal a life as possible. This objective can be accomplished only by teaching families and school personnel how to manage the child's daily therapeutic needs.