Vessel Curvature Research Articles

Retinal vasculature classification using novel multifractal features

Retinal blood vessels have been implicated in a large number of diseases including diabetic retinopathy and cardiovascular diseases, which cause damages to retinal blood vessels. The availability of retinal vessel imaging provides an excellent opportunity for monitoring and diagnosis of retinal diseases, and automatic analysis of retinal vessels will help with the processes. However, state of the art vascular analysis methods such as counting the number of branches or measuring the curvature and diameter of individual vessels are unsuitable for the microvasculature. There has been published research using fractal analysis to calculate fractal dimensions of retinal blood vessels, but so far there has been no systematic research extracting discriminant features from retinal vessels for classifications. This paper introduces new methods for feature extraction from multifractal spectra of retinal vessels for classification. Two publicly available retinal vascular image databases are used for the experiments, and the proposed methods have produced accuracies of 85.5% and 77% for classification of healthy and diabetic retinal vasculatures. Experiments show that classification with multiple fractal features produces better rates compared with methods using a single fractal dimension value. In addition to this, experiments also show that classification accuracy can be affected by the accuracy of vessel segmentation algorithms.

Disturbed Laminar Blood Flow Vastly Augments Lipoprotein Retention in the Artery Wall: A Key Mechanism Distinguishing Susceptible From Resistant Sites.

Atherosclerosis develops initially at branch points and in areas of high vessel curvature. Moreover, experiments in hypercholesterolemic mice have shown that the introduction of disturbed flow in straight, atherosclerosis-resistant arterial segments turns them highly atherosclerosis susceptible. Several biomechanical mechanisms have been proposed, but none has been demonstrated. In the present study, we examined whether a causal link exists between disturbed laminar flow and the ability of the arterial wall to retain lipoproteins. Lipoprotein retention was detected at natural predilection sites of the murine thoracic aorta 18 hours after infusion of fluorescently labeled low-density lipoprotein. To test for causality between blood flow and the ability of these areas to retain lipoproteins, we manipulated blood flow in the straight segment of the common carotid artery using a constrictive collar. Disturbed laminar flow did not affect low-density lipoprotein influx, but increased the ability of the artery wall to bind low-density lipoprotein. Concordantly, disturbed laminar flow led to differential expression of genes associated with phenotypic modulation of vascular smooth muscle cells, increased expression of proteoglycan core proteins associated with lipoprotein retention, and of enzymes responsible for chondroitin sulfate glycosaminoglycan synthesis and sulfation. Blood flow regulates genes associated with vascular smooth muscle cell phenotypic modulation, as well as the expression and post-translational modification of lipoprotein-binding proteoglycan core proteins, and the introduction of disturbed laminar flow vastly augments the ability of a previously resistant, straight arterial segment to retain lipoproteins.

Numerical investigation of fluid–particle interactions for embolic stroke

Roughly one-third of all strokes are caused by an embolus traveling to a cerebral artery and blocking blood flow in the brain. The objective of this study is to gain a detailed understanding of the dynamics of embolic particles within arteries. Patient computed tomography image is used to construct a three-dimensional model of the carotid bifurcation. An idealized carotid bifurcation model of same vessel diameters was also constructed for comparison. Blood flow velocities and embolic particle trajectories are resolved using a coupled Euler–Lagrange approach. Blood is modeled as a Newtonian fluid, discretized using the finite volume method, with physiologically appropriate inflow and outflow boundary conditions. The embolus trajectory is modeled using Lagrangian particle equations accounting for embolus interaction with blood as well as vessel wall. Both one- and two-way fluid–particle coupling are considered, the latter being implemented using momentum sources augmented to the discretized flow equations. It was observed that for small-to-moderate particle sizes (relative to vessel diameters), the estimated particle distribution ratio—with and without the inclusion of two-way fluid–particle momentum exchange—were found to be similar. The maximum observed differences in distribution ratio with and without the coupling were found to be higher for the idealized bifurcation model. Additionally, the distribution was found to be reasonably matching the volumetric flow distribution for the idealized model, while a notable deviation from volumetric flow was observed in the anatomical model. It was also observed from an analysis of particle path lines that particle interaction with helical flow, characteristic of anatomical vasculature models, could play a prominent role in transport of embolic particle. The results indicate therefore that flow helicity could be an important hemodynamic indicator for analysis of embolus particle transport. Additionally, in the presence of helical flow, and vessel curvature, inclusion of two-way momentum exchange was found to have a secondary effect for transporting small to moderate embolus particles—and one-way coupling could be used as a reasonable approximation, thereby causing substantial savings in computational resources.

Analytical modeling of drug dynamics induced by eluting stents in the coronary multi-layered curved domain

Pharmacokinetics induced by drug eluting stents (DES) in coronary walls is modeled by means of a one-dimensional multi-layered model, accounting for vessel curvature and non-homogeneous properties of the arterial tissues. The model includes diffusion mechanisms, advection effects related to plasma filtration through the walls, and bio-chemical drug reactions. A non-classical Sturm–Liouville problem with discontinuous coefficients is derived, whose closed-form analytical solution is obtained via an eigenfunction expansion. Soundness and consistency of the proposed approach are shown by numerical computations based on possible clinical treatments involving both hydrophilic and hydrophobic drugs. The influence of the main model parameters on drug delivery mechanisms is analyzed, highlighting the effects induced by vessel curvature and yielding comparative indications and useful insights into the concurring mechanisms governing the pharmacokinetics.

Microcatheter Shaping for Intracranial Aneurysm Coiling Using the 3-Dimensional Printing Rapid Prototyping Technology: Preliminary Result in the First 10 Consecutive Cases

An optimal microcatheter is necessary for successful coiling of an intracranial aneurysm. The optimal shape may be predetermined before the endovascular surgery via the use of a 3-dimensional (3D) printing rapid prototyping technology. We report a preliminary series of intracranial aneurysms treated with a microcatheter shape determined by the patient's anatomy and configuration of the aneurysm, which was fabricated with a 3D printer aneurysm model. A solid aneurysm model was fabricated with a 3D printer based on the data acquired from the 3D rotational angiogram. A hollow aneurysm model with an identical vessel and aneurysm lumen to the actual anatomy was constructed with use of the solid model as a mold. With use of the solid model, a microcatheter shaping mandrel was formed to identically line the 3D curvature of the parent vessel and the long axis of the aneurysm. With use of the mandrel, a test microcatheter was shaped and validated for the accuracy with the hollow model. All the planning processes were undertaken at least 1 day before treatment. The preshaped mandrel was then applied in the endovascular procedure. Ten consecutive intracranial aneurysms were coiled with the pre-planned shape of the microcatheter and evaluated for the clinical and anatomical outcomes and microcatheter accuracy and stability. All of pre-planned microcatheters matched the vessel and aneurysm anatomy. Seven required no microguidewire assistance in catheterizing the aneurysm whereas 3 required guiding of a microguidewire. All of the microcatheters accurately aligned the long axis of the aneurysm. The pre-planned microcatheter shapes demonstrated stability in all except in 1 large aneurysm case. When a 3D printing rapid type prototyping technology is used, a patient-specific and optimal microcatheter shape may be determined preoperatively.

Distribution of tissue characteristics of coronary plaques evaluated by integrated backscatter intravascular ultrasound: Differences between the inner and outer vessel curvature

BackgroundThe purpose of the present study was to evaluate the tissue characteristics of plaques with moderate or mild stenosis in the inner and outer curvature of the left anterior descending artery (LAD) using integrated backscatter intravascular ultrasound. MethodsWe evaluated 66 plaques with moderate stenosis (plaque burden >50% but ≤75%) and 49 plaques with mild stenosis (plaque burden >30% but ≤50%) in 66 patients undergoing percutaneous intervention to the LAD. All plaques were >10mm away from any side branch or previously implanted stents. We divided vessel cross-sections into four quadrants (inner curvature, outer curvature, clockwise lateral side, and counterclockwise lateral side) using the septal branch as a landmark for the inner curvature. We averaged relative lipid area, relative fibrous area, and relative calcified area in minimal lumen area (MLA), three cross-sections proximal to the site of MLA, and three cross-sections distal to the site of MLA. ResultsIn plaques with moderate stenosis, the relative lipid area in the inner curvature was significantly greater than in the outer curvature and lateral sides, whereas there was no significant difference in plaques with mild stenosis. ConclusionThe present study provides new findings that lipid pool is clustered in the inner curvature and fibrous tissue is clustered in the outer curvature of plaques with moderate stenosis in non-branching LAD lesions.

The Curved MCA: Influence of Vessel Anatomy on Recanalization Results of Mechanical Thrombectomy after Acute Ischemic Stroke.

Vessel anatomy is assumed to influence results of endovascular mechanical thrombectomy using stent retrievers. The purpose of this study was to analyze the influence of vessel curvature on recanalization results in patients with acute ischemic stroke caused by large-vessel occlusion. In 159 patients (70 ± 12.8 years of age; 79 women) treated for acute ischemic stroke after carotid T and/or MCA occlusion by using stent retrievers, the following angles were measured in standard anteroposterior angiograms to describe vessel anatomy: first, between the terminal ICA segment and the most downward curved M1 segment conterminous to the proximal face of the thrombus (ICA/M1 angle); second, between the most proximal M1 segment and the segment immediately conterminous to the thrombus (M1/M1 angle); and additionally, in patients with distal M1/proximal M2 occlusion, the angle of the last curvature proximal of the thrombus (M1/M2 angle). Angles of patients with-versus-without successful recanalization were compared. Patients without successful recanalization (TICI 0-2a) showed significantly larger ICA/M1 angles (mean, 110°± 23.8° versus 69°± 28.7°, P < .001) and significantly larger M1/M1 angles (56°± 29.2° versus 29°± 26.6°, P = .001) than patients with successful recanalization (TICI 2b/3). In patients without successful recanalization after a distal M1 or proximal M2 occlusion, the M1/M2 angle was significantly larger than that in patients with successful recanalization (117° ± 34.3° versus 67° ± 29.5°, P = .006). This retrospective analysis showed that mechanical thrombectomy in the anterior circulation was significantly less often successful in patients with large vessel angles. Therefore, vessel curvature significantly influences the results of mechanical thrombectomy with stent retrievers for treatment of acute ischemic stroke. Further work is needed to understand the underlying causality.

Short-term outcome of laparoscopic greater curvature plication – a new gastric restrictive technique for morbidly obese patients

Introduction: Gastric restrictive procedures as a surgical option for treatment of morbid obesity include either gastric resection, such as vertical sleeve gastrectomy, or the use of a prosthetic device, such as adjustable gastric banding. Objectives: The present study aimed to report the results of laparoscopic greater curvature plication (LGCP) as a new gastric restrictive procedure without the need for gastric resection by staple or the use of prosthesis. Materials and methods: This was a prospective study, which included 32 patients (19 female and 13 male) who underwent LGCP between May 2012 and June 2013 with a mean body mass index of 41.75±3.8kg/m2 and mean age of 32.5±8.6 years. Via a five-trocar port technique, dissection of the greater omentum from the greater curvature and ligation of short gastric vessels were carried out, followed by plication of the greater curvature by two rows of sutures over a 32-Fr bougie to ensure a patent lumen. Follow up of total weight loss and excess weight loss (EWL) for all cases were recorded at 1, 3, 6 and 12 months. Results: All procedures were carried out laparoscopically without the need for conversion. There were no intraoperative complications detected. Mean operative time was 83±7.5 minutes and mean hospital stay was 36.4±6.1hours. Post-operative nausea, vomiting and sialorrhea occurred in 7 patients (21.9%), 5 patients (15.6%) and 10 patients (31.25%), respectively, which disappeared within 1– 2 weeks. Mean EWL after 1, 3, 6 and 12 months was 19.5%, 30.5%, 47% and 59%, respectively. There is no weight gain recorded to date in any of the patients. Conclusions: LGCP is a new gastric restrictive technique that is both safe and effective. However, long-term follow-up and large prospective randomized controlled studies are still needed. Acknowledgements: Special thanks to the doctors who provided the chance and guidance to participate in this study.

Deployment of stent grafts in curved aneurysmal arteries: toward a predictive numerical tool.

The mechanical behavior of aortic stent grafts plays an important role in the success of endovascular surgery for aneurysms. In this study, finite element analysis was carried out to simulate the expansion of five marketed stent graft iliac limbs and to evaluate quantitatively their mechanical performances. The deployment was modeled in a simplified manner according to the following steps: (i) stent graft crimping and insertion in the delivery sheath, (ii) removal of the sheath and stent graft deployment in the aneurysm, and (iii) application of arterial pressure. In the most curved aneurysm and for some devices, a decrease of stent graft cross-sectional area up to 57% was found at the location of some kinks. Apposition defects onto the arterial wall were also clearly evidenced and quantified. Aneurysm inner curve presented significantly more apposition defects than outer curve. The feasibility of finite element analysis to simulate deployment of marketed stent grafts in curved aneurysm models was demonstrated. The study of the influence of aneurysm tortuosity on stent graft mechanical behavior shows that increasing vessel curvature leads to stent graft kinks and inadequate apposition against the arterial wall. Such simulation approach opens a very promising way toward surgical planning tools able to predict intra and/or post-operative short-term stent graft complications.

The pREset Stent Retriever for Endovascular Treatment of Stroke Caused by MCA Occlusion: Safety and Clinical Outcome.

PurposeThe purpose of this study was to analyze the safety and efficacy of the pREset device, a stent retriever system, for endovascular mechanical thrombectomy (MT) in acute ischemic stroke (AIS) after middle cerebral artery (MCA) occlusion.MethodsRetrospectively, 48 consecutive patients (mean age ± standard deviation, 71.0 ± 11.9 years; 24 women) treated for acute MCA occlusion using pREset solely or in combination with other MT devices were identified. Recanalization success was evaluated using the modified thrombolysis in cerebral infarction score (TICI), and complications were detected by 24-h follow-up computed tomography or magnetic resonance imaging. MCA anatomy was assessed in angiograms. Clinical outcome was evaluated with National Institutes of Health Stroke Scale (NIHSS) score at admission and discharge, and modified Rankin scale (mRS) score at discharge and follow-up.ResultsSuccessful recanalization (TICI 2b/3) was achieved in 39 patients (81.3 %). Rate of procedure-related complications was 8.3 %. In four patients, a subarachnoid hemorrhage occurred (8.3 %), and parenchymal hematoma was detected in four patients (8.3 %). None of those events was associated with clinical deterioration. MCA curvature significantly influenced recanalization success (P < 0.005).Successful recanalization correlated significantly with lower NIHSS scores and favorable clinical outcome (mRS score 0–2) at discharge (P < 0.05). Mortality within 90 days was significantly lower in patients with TICI 2b/3 (P < 0.005).ConclusionsHigh recanalization rates, low complication rates, and a significantly improved outcome after successful recanalization strongly suggest that MT with pREset is an adequate therapy for AIS after MCA occlusion. Vessel curvature is a significant determining factor for recanalization success.

Synergy between shear-induced migration and secondary flows on red blood cells transport in arteries: considerations on oxygen transport.

Shear-induced migration of red blood cells (RBCs) is a well-known phenomenon characterizing blood flow in the small vessels (micrometre to millimetre size) of the cardiovascular system. In large vessels, like the abdominal aorta and the carotid artery (millimetre to centimetre size), the extent of this migration and its interaction with secondary flows has not been fully elucidated. RBC migration exerts its influence primarily on platelet concentration, oxygen transport and oxygen availability at the luminal surface, which could influence vessel wall disease processes in and adjacent to the intima. Phillips' shear-induced particle migration model, coupled to the Quemada viscosity model, was employed to simulate the macroscopic behaviour of RBCs in four patient-specific geometries: a normal abdominal aorta, an abdominal aortic aneurysm (AAA), a normal carotid bifurcation and a stenotic carotid bifurcation. Simulations show a migration of RBCs from the near-wall region with a lowering of wall haematocrit (volume fraction of RBCs) on the posterior side of the normal aorta and on the lateral-external side of the iliac arteries. A marked migration is observed on the outer wall of the carotid sinus, along the common carotid artery and in the carotid stenosis. No significant migration is observed in the AAA. The spatial and temporal patterns of wall haematocrit are correlated with the near-wall shear layer and with the secondary flows induced by the vessel curvature. In particular, secondary flows accentuate the initial lowering in RBC near-wall concentration by convecting RBCs from the inner curvature side to the outer curvature side. The results reinforce data in literature showing a decrease in oxygen partial pressure on the inner curvature wall of the carotid sinus induced by the presence of secondary flows. The lowering of wall haematocrit is postulated to induce a decrease in oxygen availability at the luminal surface through a diminished concentration of oxyhaemoglobin, hence contributing, with the reported lowered oxygen partial pressure, to local hypoxia.

Curvature effect on hemodynamic conditions at the inner bend of the carotid siphon and its relation to aneurysm formation

Although high-impact hemodynamic forces are thought to lead to cerebral aneurysmal change, little is known about the aneurysm formation on the inner aspect of vascular bends such as the internal carotid artery (ICA) siphon where wall shear stress (WSS) is expected to be low. This study evaluates the effect of vessel curvature and hemodynamics on aneurysm formation along the inner carotid siphon. Catheter 3D-rotational angiographic volumes of 35 ICA (10 aneurysms, 25 controls) were evaluated in 3D for radius of curvature and peak curvature of the siphon bend, followed by univariate statistical analysis. Computational fluid dynamic (CFD) simulations were performed on patient-derived models after aneurysm removal and on synthetic variants of increasing curvature. Peak focal siphon curvature was significantly higher in aneurysm bearing ICAs (0.36±0.045 vs. 0.30±0.048mm−1, p=0.003), with no difference in global radius of curvature (p=0.36). In CFD simulations, increasing parametric curvature tightness (from 5 to 3mm radius) resulted in dramatic increase of WSS and WSS gradient magnitude (WSSG) on the inner wall of the bend. In patient-derived data, the location of aneurysms coincided with regions of low WSS (<4Pa) flanked by high WSS and WSSG peaks. WSS peaks correlated with the aneurysm neck. In contrast, control siphon bends displayed low, almost constant, WSS and WSSG profiles with little spatial variation. High bend curvature induces dynamically fluctuating high proximal WSS and WSSG followed by regions of flow stasis and recirculation, leading to local conditions known to induce destructive vessel wall remodeling and aneurysmal initiation.

SPECTRAL NUMERICAL SIMULATION OF MAGNETO-PHYSIOLOGICAL LAMINAR DEAN FLOW

A computational simulation of magnetohydrodynamic laminar blood flow under pressure gradient through a curved bio-vessel, with circular cross-section is presented. Electrical conductivity and other properties of the biofluid (blood) are assumed to be invariant. A Newtonian viscous flow (Navier–Stokes magnetohydrodynamic) model is employed which is appropriate for large diameter blood vessels, as confirmed in a number of experimental studies. Rheological effects are therefore neglected as these are generally only significant in smaller diameter vessels. Employing a toroidal coordinate system, the steady-state, three-dimensional mass and momentum conservation equations are developed. With appropriate transformations, the transport model is non-dimensionalized and further simplified to a pair of axial and secondary flow momenta equations with the aid of a stream function. The resulting non-linear boundary value problem is solved with an efficient, spectral collocation algorithm, subject to physically appropriate boundary conditions. The influence of magnetic body force parameter, Dean number and vessel curvature on the flow characteristics is examined in detail. For high magnetic parameter and Dean number and low curvature, the axial flow is observed to be displaced toward the center of the vessel with corresponding low fluid particle vorticity strengths. Visualization is achieved with the MAPLE software. The simulations are relevant to cardiovascular biomagnetic flow control.

Effect of structural remodeling (retraction and recoil) of the pipeline embolization device on aneurysm occlusion rate.

During endovascular treatment of unruptured aneurysms with the Pipeline Embolization Device, an oversized device is often selected to achieve better wall apposition; however, this device oversizing could be related to overelongation and possible delayed enlargement of the stented region. The purpose of this study is to investigate the relationship between oversize and treatment outcome. The DynaCT images of 14 aneurysms treated by a single Pipeline Embolization Device were retrospectively analyzed. 3D images of the deployed device were compared with those acquired at the 6-month follow-up for qualitative and quantitative evaluation. The diameter and length of the Pipeline Embolization Device were measured at both time points and compared for determination of the device changes. Structural changes of the device have been observed, and it was found that the Pipeline Embolization Device influences the vessel curvature in some cases. On average, it increases its diameter by 0.23 mm and decreases its length by 2.88 mm within 6 months of initial deployment. Excessive elongation beyond its nominal length is correlated with a lower aneurysm occlusion rate at the 6-month follow-up. Not only does a Pipeline Embolization Device reconstruct the aneurysm and parent artery, but its entire structure goes through a gradual remodeling process. The relative deformation between the device and the artery indicates suboptimal wall apposition. Device oversizing does not have a direct effect on shortening or recoil. The aneurysm occlusion rate, however, is lowered by overelongation of the Pipeline Embolization Device.

Human coronary plaque wall thickness correlated positively with flow shear stress and negatively with plaque wall stress: an IVUS-based fluid-structure interaction multi-patient study

BackgroundAtherosclerotic plaque progression and rupture are believed to be associated with mechanical stress conditions. In this paper, patient-specific in vivo intravascular ultrasound (IVUS) coronary plaque image data were used to construct computational models with fluid-structure interaction (FSI) and cyclic bending to investigate correlations between plaque wall thickness and both flow shear stress and plaque wall stress conditions.MethodsIVUS data were acquired from 10 patients after voluntary informed consent. The X-ray angiogram was obtained prior to the pullback of the IVUS catheter to determine the location of the coronary artery stenosis, vessel curvature and cardiac motion. Cyclic bending was specified in the model representing the effect by heart contraction. 3D anisotropic FSI models were constructed and solved to obtain flow shear stress (FSS) and plaque wall stress (PWS) values. FSS and PWS values were obtained for statistical analysis. Correlations with p < 0.05 were deemed significant.ResultsNine out of the 10 patients showed positive correlation between wall thickness and flow shear stress. The mean Pearson correlation r-value was 0.278 ± 0.181. Similarly, 9 out of the 10 patients showed negative correlation between wall thickness and plaque wall stress. The mean Pearson correlation r-value was -0.530 ± 0.210.ConclusionOur results showed that plaque vessel wall thickness correlated positively with FSS and negatively with PWS. The patient-specific IVUS-based modeling approach has the potential to be used to investigate and identify possible mechanisms governing plaque progression and rupture and assist in diagnosis and intervention procedures. This represents a new direction of research. Further investigations using more patient follow-up data are warranted.

High curvature of the internal carotid artery is associated with the presence of intracranial aneurysms

ObjectiveAneurysm formation in locations not involving vascular bifurcations has not been thoroughly analyzed. This study evaluated the relationship between the degree of vessel curvature and the presence of intracranial sidewall...

Simulation of oxygen transfer in stented arteries and correlation with in‐stent restenosis

Computational models are used to study the combined effect of biomechanical and biochemical factors on coronary in-stent restenosis, which is a postoperative remodeling and regrowth pathology of the stented arteries. More precisely, we address numerical simulations, on the basis of Navier-Stokes and mass transport equations, to study the role of perturbed wall shear stresses and reduced oxygen concentration in a geometrical model reconstructed from a real porcine artery treated with a stent. Joining in vivo and in silico tools of investigation has multiple benefits in this case. On one hand, the geometry of the arterial wall and of the stent closely correspond to a real implanted configuration. On the other hand, the inspection of histological tissue samples informs us on the location and intensity of in-stent restenosis. As a result, we are able to correlate geometrical factors, such as the axial variation of the artery diameter and its curvature; the numerical quantification of biochemical stimuli, such as wall shear stresses; and the availability of oxygen to the inner layers of the artery, with the appearance of in-stent restenosis. This study shows that the perturbation of the vessel curvature could induce hemodynamic conditions that stimulate undesired arterial remodeling.

Accuracy and Reproducibility of a Novel Dynamic Volume Flow Measurement Method

In clinical practice, blood volume flow (BVF) is typically calculated assuming a perfect parabolic and axisymmetric velocity distribution. This simple approach cannot account for the complex flow configurations that are produced by vessel curvatures, pulsatility and diameter changes and, therefore, results in a poor estimation. Application of the Womersley model allows compensation for the flow distortion caused by pulsatility and, with some adjustment, the effects of slight curvatures, but several problems remain unanswered. Two- and three-dimensional approaches can acquire the actual velocity field over the whole vessel section, but are typically affected by a limited temporal resolution. The multigate technique allows acquisition of the actual velocity profile over a line intersecting the vessel lumen and, when coupled with a suitable wall-tracking method, can offer the ideal trade-off among attainable accuracy, temporal resolution and required calculation power. In this article, we describe a BVF measurement method based on the multigate spectral Doppler and a B-mode edge detector algorithm for wall-position tracking. The method has been extensively tested on the research platform ULA-OP, with more than 1700 phantom measurements at flow rates between 60 and 750 mL/min, steering angles between 10° and 22° and constant, sinusoidal or pulsed flow trends. In the averaged BVF measurement, we found an underestimation of about −5% and a coefficient of variability (CV) less than 6%. In instantaneous measurements (e.g., systolic peak) the CV was in the range 2%–8.5%. These results were confirmed by a preliminary test on the common carotid artery of 10 volunteers (CV = 2%–11%).

Sol ön inen koroner arterde akordiyon fenomeni

Accordion phenomenon , during routine angioplasty procedure, is produced by mechanical alteration of the geometry and curvature of a tortuous vessel by stiff PCI wire, resulting in invagination and shortening of the vessel wall. It has been described in all coronary arteries and left internal mammary artery graft but left anterior descending is very rare. Given the possible serious alternative diagnoses there cognition of the accordion effect is important and may prevent unnecessary interventions.

Viscoelasticity of blood and viscoelastic blood analogues for use in polydymethylsiloxane in vitro models of the circulatory system.

The non-Newtonian properties of blood are of great importance since they are closely related with incident cardiovascular diseases. A good understanding of the hemodynamics through the main vessels of the human circulatory system is thus fundamental in the detection and especially in the treatment of these diseases. Very often such studies take place in vitro for convenience and better flow control and these generally require blood analogue solutions that not only adequately mimic the viscoelastic properties of blood but also minimize undesirable optical distortions arising from vessel curvature that could interfere in flow visualizations or particle image velocimetry measurements. In this work, we present the viscoelastic moduli of whole human blood obtained by means of passive microrheology experiments. These results and existing shear and extensional rheological data for whole human blood in the literature enabled us to develop solutions with rheological behavior analogous to real whole blood and with a refractive index suited for PDMS (polydymethylsiloxane) micro- and milli-channels. In addition, these blood analogues can be modified in order to obtain a larger range of refractive indices from 1.38 to 1.43 to match the refractive index of several materials other than PDMS.