Behavior Of Vessel Wall Research Articles

Integrated assessment of temporal, structural and spatial parameters of dynamic retinal vessel behaviour in diabetes mellitus type 1

AbstractVascular risk factors contribute to the development of diabetes mellitus. Dynamic retinal vessel analysis is usually defined as non‐invasive clinical observation of the reaction of retinal vessels to a physiological stimulus. The data which is thus generated may be further analysed with respect to dynamic time‐dependent and spatial vessel behaviour. We assume that assessment of different aspects of retinal vessel dynamics highlights different peculiarities of the underlying disease and allow for specific and sensitive characterization of vascular pathology. This concept of multimodal analysis of pathologic retinal vessel behaviour was performed for the example of diabetes mellitus type 1 (DM1). 35 untreated DM1 patients with no or non‐proliferative retinopathy and 35 age and gender matched medically healthy volunteers were examined by Dynamic Vessel Analyser (DVA, IMEDOS, Jena, Germany). Different aspects of dynamic retinal vessel behaviour were evaluated. Together with the examination of retinal vessel reaction to flickering light unstimulated vessel wall behaviour and pulse wave propagation were assessed using mathematical signal analysis. Additionally differences in amplitude and frequency of spatial vessel diameter changes along the measured vessel segments were analysed to assess the microstructure of retinal vascular blood columns. Significant differences in several structural and functional parameters of retinal vessels in diabetes mellitus type 1 were found. Particularly retinal vessel dilation in response to flickering light was diminished both in arteries as well as in veins and delayed in arteries; longitudinal sections of retinal arteries in DM1 patients without retinopathy possessed more mid frequency roughness (one oscillation in ~250 ÷ 416 μm) than longitudinal sections of patients with retinopathy; both retinal venous pulsations (period <1.5 s) and vasomotions (period ≥1.5 s) showed higher rate of periodicity in DM1 than in the control group. These results might indicate alterations in vascular endothelial function, smooth musculature and retinal vessel wall rigidity in diabetes mellitus, leading to altered perfusion and vascular regulation following metabolic demand in the central microcirculation. Dynamic vessel analysis includes valuable information beyond conventional DVA evaluation of temporal vessel reaction to flicker. This allows for detailed individual characterization of vascular damage and further understanding of underlying disease pathology.

Dynamic retinal vessel analysis in Alzheimer's disease

AbstractVascular risk factors contribute to the development of Alzheimer's disease. Retinal vessels are similar to cerebral vessels in their structure and function. Dynamic retinal vessel analysis is usually defined as non‐invasive clinical observation of the reaction of retinal vessels to a physiological stimulus. The data which is thus generated may be further analysed with respect to dynamic time‐dependent and spatial vessel behaviour. We apply this principle of integrated analysis of pathologic dynamic retinal vessel behaviour in order to reveal microvascular alterations in the retina in Alzheimer's disease dementia. Four different aspects of dynamic retinal vessel behaviour were evaluated: together with the assessment of retinal vessel reaction to flickering light unstimulated vessel wall behaviour and pulse wave propagation were assessed using mathematical signal analysis. Additionally differences in amplitude and frequency of spatial vessel diameter changes along the measured vessel segments were analysed to assess the microstructure of retinal vascular blood columns. Significant differences in several structural and functional parameters of retinal vessels in Alzheimer's disease dementia were found. The results might indicate alterations in neuro‐vascular coupling, vascular endothelial function, smooth musculature and retinal vessel wall rigidity in this disease, leading to altered perfusion and vascular regulation following metabolic demand in the central microcirculation.

Creep deformation and damage behavior of reactor pressure vessel under core meltdown scenario

The Fukushima accident shows that In-Vessel Retention (IVR) of molten core debris has not been appropriately assessed, and a certain pressure (upto 8.0 MPa) still exists inside the reactor pressure vessel (RPV). Generally, the pressure was supposed to be successfully released, and the externally cooled lower head wall mainly experienced the temperature difference which may be more than 1000 °C. Therefore, in order to make the IVR succeed, it is necessary to investigate the creep behavior and damage distribution of the RPV under complex thermal-mechanical loadings. Accordingly, considering the unlikely core meltdown scenario as a severe accident condition, the failure site and time have to be predicted for a safety assessment purpose. Due to heavy thick wall of the RPV, the high temperature gradient inevitably results in various failure modes, i.e., plastic failure and creep failure. In disclosing it, the finite element model (FEM) has been developed for simulating the failure processes and the visco-plastic behavior of vessel wall. In accounting for the most dangerous situation, the critical heat flux (CHF) loading is applied on the RPV as a limit boundary. Subsequently, some failure modes has been found as local melting, plastic damage and creep damage by FEM. Furthermore, it is found that the RPV failure varies with the internal pressures. For the situation of low pressure and high temperature, the failure dominated by creep takes place at the hot focus site. With the further increase of pressure, the thinnest wall thickness is weakest for maintaining the RPV integrity, the damage of which initiates at the outside of RPV by plasticity. Besides, the multiaxial state of stress is found to accelerate the damage evolution on the thinnest site, and the uniaxial failure criterion underestimate the damage accumulation.

Biomechanical analysis of the splenic avulsion mechanism.

The spleen is a frequently injured abdominal organ in road accidents, with an injury frequency close to 30%. The splenic avulsion exhibit a significant ratio of morbidity. It is clinically described as the complete failure of the pancreatico-splenic ligament (PSL) which is composed of splenic vessels and connective tissues. What are the biomechanical mechanisms involved with spleen avulsion? Is it possible to quantify tolerance levels of PSL structure? The current work combines both experimental and finite element (FE) investigations to determine the splenic avulsion process. Tensile tests on 13 PSL samples were performed up to failure. The experimental results provide reference data for model validation and showed a failure process starting at a peak force of 70±34 N combined with a peak strain of 105±26%. In an attempt to identify possible vessel ruptures within the PSL, a FE model of the PSL was developed including both vessels and connective tissues. The vessel wall behaviour up to failure was reproduced using an Ogden law and calibrated by inverse analysis according to literature data. The connective tissues function was modelled by a cohesion-loss interface. Once model correlation to experimental results was achieved, numerical simulation revealed that haemorrhage could occur even before the maximum peak is reached. Indeed, the first vessel ruptures were recorded at a strain of 92% at the upper lobe vein.

The edge vascular response following implantation of the Absorb everolimus-eluting bioresorbable vascular scaffold and the XIENCE V metallic everolimus-eluting stent. First serial follow-up assessment at six months and two years: insights from the first-in-man ABSORB Cohort B and SPIRIT II trials

To assess serially the edge vascular response (EVR) of a bioresorbable vascular scaffold (BVS) compared to a metallic everolimus-eluting stent (EES). Non-serial evaluations of the Absorb BVS at one year have previously demonstrated proximal edge constrictive remodelling and distal edge changes in plaque composition with increase of the percent fibro-fatty (FF) tissue component. The 5 mm proximal and distal segments adjacent to the implanted devices were investigated serially with intravascular ultrasound (IVUS), post procedure, at six months and at two years, from the ABSORB Cohort B1 (n=45) and the SPIRIT II (n=113) trials. Twenty-two proximal and twenty-four distal edge segments were available for analysis in the ABSORB Cohort B1 trial. In the SPIRIT II trial, thirty-three proximal and forty-six distal edge segments were analysed. At the 5-mm proximal edge, the vessels treated with an Absorb BVS from post procedure to two years demonstrated a lumen loss (LL) of 6.68% (-17.33; 2.08) (p=0.027) with a trend toward plaque area increase of 7.55% (-4.68; 27.11) (p=0.06). At the 5-mm distal edge no major changes were evident at either time point. At the 5-mm proximal edge the vessels treated with a XIENCE V EES from post procedure to two years did not show any signs of LL, only plaque area decrease of 6.90% (-17.86; 4.23) (p=0.035). At the distal edge no major changes were evident with regard to either lumen area or vessel remodelling at the same time point. The IVUS-based serial evaluation of the EVR up to two years following implantation of a bioresorbable everolimus-eluting scaffold shows a statistically significant proximal edge LL; however, this finding did not seem to have any clinical implications in the serial assessment. The upcoming imaging follow-up of the Absorb BVS at three years is anticipated to provide further information regarding the vessel wall behaviour at the edges.

Dynamic assessment of carotid plaque motion

Assessment of dynamic plaque behaviour may help identify vulnerable carotid plaque before rupture and hence has potential clinical value for screening patients at risk of stroke. The aim of this study was to develop non-invasive ultrasound methods for quantifying dynamic plaque and vessel wall behaviour and assess their potential clinical utility. Ultrasound data from the carotid arteries of one normal subject and four patients with atherosclerotic disease were acquired using a 10 MHz linear array transducer recording raw RF/IQ data at a frame rate up to 80 Hz for 3–6 seconds. Image reconstruction and processing was performed using Matlab. Speckle tracking techniques were developed to characterize: (1) intraplaque deformation; and (2) plaque surface and vessel wall motion. Speckle tracking techniques were able to measure the range of intraplaque tissue deformation (–1.3 to 1.7 mm), plaque surface displacement (0.2–0.7 mm) and vessel wall radial strain (0.02–0.13) throughout the cardiac cycle. The feasibility of using an intraplaque deformation parameter, based on the deformation of a square template, is demonstrated. Speckle tracking techniques can be used to assess dynamic carotid plaque behaviour. Further work is required to evaluate how best to quantify biomechanical behaviour to help predict plaque rupture and hence improve risk stratification models for stroke.

401 複雑性の科学による血管壁不安定挙動の非侵襲診断(学生賞III)

401 複雑性の科学による血管壁不安定挙動の非侵襲診断(学生賞III)

Modelling of flow and wall behaviour in a mildly stenosed tube

In the present computational analysis, pulsatile flow and vessel wall behaviour in a simplified model of a stenosed vessel were investigated. Geometry of a 45% axisymmetrically stenosed (by area) cylindrical tube and a sinusoidal inflow waveform were simulated, with the fluid being assumed to be incompressible and Newtonian. The vessel wall was treated as a thick-walled, incompressible and isotropic material with uniform mechanical properties across the normal as well as the constricted segment. The study of fluid flow and wall motion was initially carried out separately using two commercial codes CFX4.2 and ABAQUS7 respectively. Their combined effects and interactions were later investigated through an iteratively coupled algorithm. Model validations on the rigid-wall fluid and static no-flow solid models were satisfactory, with Root Mean Square deviations of around 7% in centreline axial velocity between the prediction and measurement values for the rigid wall stenosis model, and 5% in circumferential stress for a cylindrical tube model under static loading when compared with the analytical solution. Results on velocity profiles, wall shear stress, intramural strain and stress for the rigid and compliant cases were all presented. Comparison between the rigid and compliant models revealed that, the flow separation layer distal to the stenosis was thicker and longer, and wall shear stress was slightly lower in the compliant model by less than 7.2%. Results obtained from the static wall model (with uniform pressure loading) and coupled fluid/wall interaction modelling of pulsatile flow showed qualitatively similar wall strain and stress patterns but considerable differences in magnitude. The radial and axial stresses were reduced by 31 and 8%, while the circumferential stress was increased by 13% due to the presence of pulsatile flow. Under the flow and structural conditions investigated, the effects of wall compliance were small, and did not change the flow and solid behaviours qualitatively in this case.