稳恒流下腹主动脉旁瘤超声多普勒血流信号的仿真分析

腹主动脉旁瘤超声多普勒血流信号的仿真研究,可以为采用超声多普勒技术检测腹主动脉旁瘤的形成、生长过程和估计动脉旁瘤瘤体大小提供指导。先通过有限元数值计算方法得到稳恒流下腹主动脉旁瘤区域内的血液流场分布,然后采用余弦叠加的合成方法仿真出相应的超声多普勒血流信号,最后对仿真信号进行频谱分析,计算其平均频率,并研究它与腹主动脉旁瘤瘤体大小的关系。结果表明：当动脉旁瘤较小时,平均频率的幅度变化较小;当动脉旁瘤较大时,平均频率的幅度变化较大。因此,采用平均频率的幅度变化可以在一定程度上估计动脉旁瘤的瘤体大小。     

INSERTION OF AN INTRAAORTIC BALLOON THROUGH A LIMB OF AN AORTOFEMORAL GRAFT AFTER AORTIC VALVE REPLACEMENT, DOUBLE CORONARY ARTERY BYPASS, AND RESECTION OF AN ABDOMINAL AORTIC ANEURYSM

This case report describes a useful and unusual route for insertion of an intraaortic balloon in 63-year-old man who was operated upon for calcific aortic stenosis, coronary atherosclerosis involving the left anterior descending and right coronary arteries, and a large abdominal aortic aneurysm. Aortic valve replacement was accomplished with a porcine heterograft prosthesis. Bypasses to the left anterior descending and right coronary arteries were constructed with reversed saphenous vein grafts, and the abdominal aneurysm was resected and repaired with a bifurcated woven Dacron vascular graft. An electively placed intraaortic balloon was inserted through the right limb of the aortic graft prosthesis and used to assist the patient during the immediate postoperative period. Uneventful recovery ensued.     

Metabolism of eicosanoids and their action on renal function during ischaemia and reperfusion: the effect of alprostadil

Eicosanoids, active metabolites of arachidonic acid (AA), play an important role in the regulation of renal haemodynamics and glomerular filtration. Our study verified the hypothesis on the positive action of exogenously administered PGE(1) on renal function during an operation with temporary ischaemia of the lower half of the body. Also the effect of alprostadil (prostaglandin E(1) analogue) administered during the operation of an abdominal aorta aneurysm on the postoperative systemic metabolism of AA and the glomerular filtration rate (GFR) was investigated. The study included 42 patients with a diagnosed abdominal aorta aneurysm who have been qualified for the operation of implantation of the aortic prosthesis. The patients were randomly assigned to two groups: the study group (I) receiving alprostadil and the control group (II) without alprostadil. The levels of hydroxyeicosatetraenoic acids (15-HETE, 12-HETE, 5-HETE) were determined by RP-HPLC and the level of thromboxane B(2) (TxB(2)) was determined by ELISA in the plasma of the blood drawn from vena cava superior immediately before aortic clamping (A) and 5 min after aortic declamping (B). The administration of PGE(1) affects the metabolism of 15-HETE in a manner dependent on the baseline value of GFR but does not significantly change the postoperative renal function. The metabolism of 15-HETE is affected by the baseline value of GFR1 and a longer period of ischaemia is correlated with lower concentrations of 5-HETE during reperfusion. The results of our studies indicate that TxB(2) influences the postoperative function of kidneys.     

Acute occlusion of an abdominal aortic aneurysm complicated by bilateral lower extremity venous thrombosis: A case report

Acute occlusion of an abdominal aortic aneurysm is a rare phenomenon. Its possible complications include distal spasm followed by arterial thrombosis, ischemia of the distal limbs, distal embolization, acidosis, hyperkalemia, and the development of venous thrombosis of the lower limbs. Surgical correction is often complicated by cardiac decompensation, renal failure, fatal pulmonary embolism, and metabolic derangements related to toxins released from the revascularized limb. Unless contraindicated, immediate systemic heparinization must be undertaken when the diagnosis is first suspected. We present a case of sudden occlusion of an abdominal aortic aneurysm complicated by venous thrombosis involving both lower extremities. After undergoing surgical revascularization, the patient sustained massive fatal pulmonary emboli. Prophylactic interruption of the inferior vena cava may be indicated in patients who present with this complication of abdominal aortic aneurysm.     

Vascular wall flow-induced forces in a progressively enlarged aneurysm model

The current study is focused on the numerical investigation of the flow field induced by the unsteady flow in the vicinity of an abdominal aortic aneurysm model. The computational fluid dynamics code used is based on the finite volume method, and it has already been used in various bioflow studies. For modelling the rheological behaviour of blood, the Quemada non-Newtonian model is employed, which is suitable for simulating the two-phase character of blood namely a suspension of blood cells in plasma. For examining its non-Newtonian effects a comparison with a corresponding Newtonian flow is carried out. Furthermore, the investigation is focused on the distribution of the flow-induced forces on the interior wall of the aneurysm and in order to study the development of the distribution with the gradual enlargement of the aneurysm, three different degrees of aneurysm-growth have been assumed. Finally and for examining the effect of the distribution on the aneurysm growth, a comparison is made between the pressure and wall shear-stress distributions at the wall for each growth-degree.     

Vascular wall flow-induced forces in a progressively enlarged aneurysm model

The current study is focused on the numerical investigation of the flow field induced by the unsteady flow in the vicinity of an abdominal aortic aneurysm model. The computational fluid dynamics code used is based on the finite volume method, and it has already been used in various bioflow studies. For modelling the rheological behaviour of blood, the Quemada non-Newtonian model is employed, which is suitable for simulating the two-phase character of blood namely a suspension of blood cells in plasma. For examining its non-Newtonian effects a comparison with a corresponding Newtonian flow is carried out. Furthermore, the investigation is focused on the distribution of the flow-induced forces on the interior wall of the aneurysm and in order to study the development of the distribution with the gradual enlargement of the aneurysm, three different degrees of aneurysm-growth have been assumed. Finally and for examining the effect of the distribution on the aneurysm growth, a comparison is made between the pressure and wall shear-stress distributions at the wall for each growth-degree.     

Patient-specific initial wall stress in abdominal aortic aneurysms with a backward incremental method

Patient-specific wall stress simulations on abdominal aortic aneurysms may provide a better criterion for surgical intervention than the currently used maximum transverse diameter. In these simulations, it is common practice to compute the peak wall stress by applying the full systolic pressure directly on the aneurysm geometry as it appears in medical images. Since this approach does not account for the fact that the measured geometry is already experiencing a substantial load, it may lead to an incorrect systolic aneurysm shape. We have developed an approach to compute the wall stress on the true diastolic geometry at a given pressure with a backward incremental method. The method has been evaluated with a neo-Hookean material law for several simple test problems. The results show that the method can predict an unloaded configuration if the loaded geometry and the load applied are known. The effect of incorporating the initial diastolic stress has been assessed by using three patient-specific geometries acquired with cardiac triggered MR. The comparison shows that the commonly used approach leads to an unrealistically smooth systolic geometry and therefore provides an underestimation for the peak wall stress. Our backward incremental modelling approach overcomes these issues and provides a more plausible estimate for the systolic aneurysm volume and a significantly different estimate for the peak wall stress. When the approach is applied with a more complex material law which has been proposed specifically for abdominal aortic aneurysm similar effects are observed and the same conclusion can be drawn.     

Long Telomeres in Blood Leukocytes Are Associated with a High Risk of Ascending Aortic Aneurysm

Ascending aortic aneurysm is a connective tissue disorder. Even though multiple novel gene mutations have been identified, risk profiling and diagnosis before rupture still represent a challenge. There are studies demonstrating shorter telomere lengths in the blood leukocytes of abdominal aortic aneurysm patients. The aim of this study was to measure whether relative telomere lengths are changed in the blood leukocytes of ascending aortic aneurysm patients. We also studied the expression of telomerase in aortic tissue samples of ascending aortic aneurysms. Relative lengths of leukocyte telomeres were determined from blood samples of patients with ascending aortic aneurysms and compared with healthy controls. Telomerase expression, both at the level of mRNA and protein, was quantified from the aortic tissue samples. Mean relative telomere length was significantly longer in ascending aortic aneurysm blood samples compared with controls (T/S ratio 0.87 vs. 0.61, p<0.001). Expressions of telomerase mRNA and protein were elevated in the aortic aneurysm samples (p<0.05 and p<0.01). Our study reveals a significant difference in the mean length of blood leukocyte telomeres in ascending aortic aneurysm and controls. Furthermore, expression of telomerase, the main compensating factor for telomere loss, is elevated at both the mRNA and protein level in the samples of aneurysmal aorta. Further studies will be needed to confirm if this change in telomere length can serve as a tool for assessing the risk of ascending aortic aneurysm.     

A New Murine Model of Endovascular Aortic Aneurysm Repair

Endovascular aneurysm exclusion is a validated technique to prevent aneurysm rupture. Long-term results highlight technique limitations and new aspects of Abdominal aortic aneurysm (AAA) pathophysiology. There is no abdominal aortic aneurysm endograft exclusion model cheap and reproducible, which would allow deep investigations of AAA before and after treatment. We hereby describe how to induce, and then to exclude with a covered coronary stentgraft an abdominal aortic aneurysm in a rat. The well known elastase induced AAA model was first reported in 1990¹ in a rat, then described in mice². Elastin degradation leads to dilation of the aorta with inflammatory infiltration of the abdominal wall and intra luminal thrombus, matching with human AAA. Endovascular exclusion with small covered stentgraft is then performed, excluding any interactions between circulating blood and the aneurysm thrombus. Appropriate exclusion and stentgraft patency is confirmed before euthanasia by an angiography thought the left carotid artery. Partial control of elastase diffusion makes aneurysm shape different for each animal. It is difficult to create an aneurysm, which will allow an appropriate length of aorta below the aneurysm for an easy stentgraft introduction, and with adequate proximal and distal neck to prevent endoleaks. Lots of failure can result to stentgraft introduction which sometimes lead to aorta tear with pain and troubles to stitch it, and endothelial damage with post op aorta thrombosis. Giving aspirin to rats before stentgraft implantation decreases failure rate without major hemorrhage. Clamping time activates neutrophils, endothelium and platelets, and may interfere with biological analysis.     

Extracellular-Purine Metabolism in Blood Vessels (Part I). Extracellular-Purine Level in Blood of Patients with Abdominal Aortic Aneurysm

Adenosine and adenosine derivatives are the main regulators of purinoceptors (P1 and P2) mediated hemostasis and blood pressure. Since impaired hemostasis and high blood pressure lead to atherosclerosis and to the development of aneurysm, in this study we tested and compared the concentration of extracellular purines (e-purines) in the blood in of patients having abdominal aortic aneurysm with that from healthy volunteers. Whereas adenine nucleosides and nucleotides level in human blood plasma was analysed using reverse phase high performance liquid chromatography (HPLC), cholesterol concentration was estimated by an enzymatic assay. We did not find any correlation between e-purines concentration and the age of healthy volunteers. Furthermore, the sum level of e-purines (ATP, ADP, AMP, adenosine, and inosine) in the control group did not exceed 70 μM, while it was nearly two-fold higher in the blood of patients having abdominal aortic aneurysm, (123 μM). In a special case of people with Leriche Syndrome, a disease characterized by deep atherosclerotic changes, the e-purines level had further increased. Additionally, we also report typical atherosclerotic changes in the aorta using histological assays as well as total cholesterol rise. The significant rise in cholesterol concentration in the blood of the patients with abdominal aortas aneurysm, compared with the control groups, was not unique since 23% of the healthy people also exceeded the normal level of cholesterol. Therefore, our results strongly indicate that the estimation of e-purines concentration in the blood may serve as another indicator of atherosclerosis and warrant further consideration as a futuristic diagnostic tool.     

Investigation of material modeling in fluid–structure interaction analysis of an idealized three-layered abdominal aorta: aneurysm initiation and fully developed aneurysms

Different material models for an idealized three-layered abdominal aorta are compared using computational techniques to study aneurysm initiation and fully developed aneurysms. The computational model includes fluid–structure interaction (FSI) between the blood vessel and the blood. In order to model aneurysm initiation, the medial region was degenerated to mimic the medial loss occurring in the inception of an aneurysm. Various cases are considered in order to understand their effects on the initiation of an abdominal aortic aneurysm. The layers of the blood vessel were modeled using either linear elastic materials or Mooney–Rivlin (otherwise known as hyperelastic) type materials. The degenerated medial region was also modeled in either linear elastic or hyperelastic-type materials and assumed to be in the shape of an arc with a thin width or a circular ring with different widths. The blood viscosity effect was also considered in the initiation mechanism. In addition, dynamic analysis of the blood vessel was performed without interaction with the blood flow by applying time-dependent pressure inside the lumen in a three-layered abdominal aorta. The stresses, strains, and displacements were compared for a healthy aorta, an initiated aneurysm and a fully developed aneurysm. The study shows that the material modeling of the vessel has a sizable effect on aneurysm initiation and fully developed aneurysms. Different material modeling of degeneration regions also affects the stress–strain response of aneurysm initiation. Additionally, the structural analysis without considering FSI (called noFSI) overestimates the peak von Mises stress by 52% at the interfaces of the layers.     

Modeling of the aorta artery aneurysms and renal artery stenosis using cardiovascular electronic system

Background  

The aortic aneurysm is a dilatation of the aortic wall which occurs in the saccular and fusiform types. The aortic aneurysms can rupture, if left untreated. The renal stenosis occurs when the flow of blood from the arteries leading to the kidneys is constricted by atherosclerotic plaque. This narrowing may lead to the renal failure. Previous works have shown that, modelling is a useful tool for understanding of cardiovascular system functioning and pathophysiology of the system. The present study is concerned with the modelling of aortic aneurysms and renal artery stenosis using the cardiovascular electronic system.     

Cathepsin A activity of a parietal thrombus of an abdominal aortic aneurysm

We evaluated the cathepsin A activity of a parietal thrombus of an abdominal aortic aneurysm. We compared this activity to that of a retracted blood clot homogenate. Cathepsin A of aneurysm parietal thrombus homogenate and blood clot homogenate showed the highest activity on Z-Phe-Ala. It was lower on Z-Phe-Phe, Z-Glu-Tyr, Z-Glu-Phe, Z-Gly-Phe, and the lowest activity was on Z-Gly-Ala. We conclude that cathepsin A's activity on a parietal thrombus of an aneurysm is much higher than blood clot cathepsin A activity.     

Fluid-structure interaction in abdominal aortic aneurysms: effects of asymmetry and wall thickness

Background  

Abdominal aortic aneurysm (AAA) is a prevalent disease which is of significant concern because of the morbidity associated with the continuing expansion of the abdominal aorta and its ultimate rupture. The transient interaction between blood flow and the wall contributes to wall stress which, if it exceeds the failure strength of the dilated arterial wall, will lead to aneurysm rupture. Utilizing a computational approach, the biomechanical environment of virtual AAAs can be evaluated to study the affects of asymmetry and wall thickness on this stress, two parameters that contribute to increased risk of aneurysm rupture.     

腔内修复术与传统开腹手术对腹主动脉瘤的治疗效果对比

目的:探讨腔内修复术与传统开腹手术在腹主动脉瘤患者治疗中的效果。方法:收集我院就诊或住院治疗的40例腹主动脉瘤患者,根据手术方式不同,将所选研究对象分为OR组和EVAR组,每组20例。OR组患者行传统开腹手术,EVAR组患者行腔内修复术。观察并比较两组患者术中出血量、输血量、手术时间、住院天数以及并发症的发生率。结果:与OR组患者相比,EVAR组患者手术出血量、输血量较少,手术时间、住院天数、ICU住院天数较短,患者围手术期的并发症发生率较低,但患者的远期并发症发生率较高(P0.05)。结论:腔内修复术与传统开腹手术相比,在手术的出血量以及患者的恢复时间等方面具有较为明显的优点,但远期的并发症发生率较高,对临床有指导意义。     

Fluid-structure interaction effects on sac-blood pressure and wall stress in a stented aneurysm

An aneurysm is a local artery ballooning greater than 50% of its nominal diameter with a risk of sudden rupture. Minimally invasive repair can be achieved by inserting surgically a stent-graft, called an endovascular graft (EVG), which is either straight tubular curved tubular or bifurcating. However post-procedural complications may arise because of elevated stagnant blood pressure in the cavity, i.e., the sac formed by the EVG and the weakened aneurysm wall In order to investigate the underlying mechanisms leading to elevated sac-pressures and hence to potentially dangerous wall stress levels and aneurysm rupture, a transient 3-D stented abdominal aortic aneurysm model and a coupled fluid-structure interaction solver were employed. Simulation results indicate that, even without the presence of endoleaks (blood flowing into the cavity), elevated sac pressure can occur due to complex fluid-structure interactions between the luminal blood flow, EVG wall, intra-sac stagnant blood, including an intra-luminal thrombus, and the aneurysm wall. Nevertheless, the impact of sac-blood volume changes due to leakage on the sac pressure and aneurysm wall stress was analyzed as well. While blood flow conditions, EVG and aneurysm geometries as well as wall mechanical properties play important roles in both sac pressure and wall stress generation, it is always the maximum wall stress that is one of the most critical parameters in aneurysm rupture prediction. All simulation results are in agreement with experimental data and clinical observations.     

The effect of asymmetry in abdominal aortic aneurysms under physiologically realistic pulsatile flow conditions

In the abdominal segment of the human aorta under a patient's average resting conditions, pulsatile blood flow exhibits complex laminar patterns with secondary flows induced by adjacent branches and irregular vessel geometries. The flow dynamics becomes more complex when there is a pathological condition that causes changes in the normal structural composition of the vessel wall, for example, in the presence of an aneurysm. This work examines the hemodynamics of pulsatile blood flow in hypothetical three-dimensional models of abdominal aortic aneurysms (AAAs). Numerical predictions of blood flow patterns and hemodynamic stresses in AAAs are performed in single-aneurysm, asymmetric, rigid wall models using the finite element method. We characterize pulsatile flow dynamics in AAAs for average resting conditions by means of identifying regions of disturbed flow and quantifying the disturbance by evaluating flow-induced stresses at the aneurysm wall, specifically wall pressure and wall shear stress. Physiologically realistic abdominal aortic blood flow is simulated under pulsatile conditions for the range of time-average Reynolds numbers 50 < or = Rem < or = 300, corresponding to a range of peak Reynolds numbers 262.5 < or = Repeak < or = 1575. The vortex dynamics induced by pulsatile flow in AAAs is depicted by a sequence of four different flow phases in one period of the cardiac pulse. Peak wall shear stress and peak wall pressure are reported as a function of the time-average Reynolds number and aneurysm asymmetry. The effect of asymmetry in hypothetically shaped AAAs is to increase the maximum wall shear stress at peak flow and to induce the appearance of secondary flows in late diastole.     

Analysis of biomechanical factors affecting stent-graft migration in an abdominal aortic aneurysm model

Focusing on a representative abdominal aortic aneurysm (AAA) with a bifurcating stent-graft (SG), a fluid-structure interaction (FSI) solver with user-supplied programs has been employed to solve for blood flow, AAA/SG deformation, sac pressure and wall stresses, as well as the downward forces acting on the SG. Simulation results indicate that implanting a SG can significantly reduce sac pressure, mechanical stress, pulsatile wall motion, and maximum diameter change in AAAs; hence, it may restore normal blood flow and prevent AAA rupture effectively. The transient SG drag force is similar in trend as the cardiac pressure. Its magnitude depends on multi-factors including blood flow conditions, as well as SG and aneurysm geometries. Specifically, AAA neck angle, iliac bifurcation angle, neck aorta-to-iliac diameter ratio, SG size, and blood waveform play important roles in generating a fluid flow force potentially leading to SG migration. It was found that the drag force can exceed 5N for an AAA with a large neck or iliac angle, wide aortic neck and narrow iliac arteries, large SG size, and/or abnormal blood waveform. Thus, the fixation of self-expandable or balloon-expandable SG contact may be inadequate to withstand the forces of blood flowing through the implant and hence means of extra fixation should be considered. A comprehensive FSI analysis of the coupled SG-AAA dynamics provides physical insight for evaluating the luminal hemodynamics, and maximum AAA-stresses as well as biomechanical factors leading potentially to SG migration.     

Secondary aortoenteric fistula

Secondary aortoenteric fistula (SAF) is an uncommon but very important complication of abdominal aortic reconstruction. The complication often occurs months to years after aortic surgery. The clinical manifestation of the aortoenteric fistula is always upper gastrointestinal bleeding. Treatment of the disease is early surgical intervention. If operative treatment is not performed promptly, the mortality is high. A case of secondary aortoduodenal fistula found 6 years after aortic reconstructive surgery, with the clinical presentation of upper gastrointestinal bleeding, is presented. On Immediate exploratory laparotomy, the proximal part of abdominal aorta was clamped. Duodenorrhaphy and aortic reconstruction with patch graft at the proximal suture line of aortic prosthesis was performed. Fortunately there was no pus, so tissue culture was not done. The intervention was concluded with an omentoplasty to protect the patch graft and to separate it from duodenorrhaphy. The patient did well after the surgical management. Because of the increasing number of elective aortic aneurysm repairs in the aging population, it is likely that more patients with secondary aortoenteric fistula will present to the clinical physicians in the future. So, a high index of suspicion is necessary for prompt diagnosis and treatment of this life-threatening event.     

The Helsinki Rat Microsurgical Sidewall Aneurysm Model

Experimental saccular aneurysm models are necessary for testing novel surgical and endovascular treatment options and devices before they are introduced into clinical practice. Furthermore, experimental models are needed to elucidate the complex aneurysm biology leading to rupture of saccular aneurysms.Several different kinds of experimental models for saccular aneurysms have been established in different species. Many of them, however, require special skills, expensive equipment, or special environments, which limits their widespread use. A simple, robust, and inexpensive experimental model is needed as a standardized tool that can be used in a standardized manner in various institutions.The microsurgical rat abdominal aortic sidewall aneurysm model combines the possibility to study both novel endovascular treatment strategies and the molecular basis of aneurysm biology in a standardized and inexpensive manner. Standardized grafts by means of shape, size, and geometry are harvested from a donor rat''s descending thoracic aorta and then transplanted to a syngenic recipient rat. The aneurysms are sutured end-to-side with continuous or interrupted 9-0 nylon sutures to the infrarenal abdominal aorta.We present step-by-step procedural instructions, information on necessary equipment, and discuss important anatomical and surgical details for successful microsurgical creation of an abdominal aortic sidewall aneurysm in the rat.