Annular Support Research Articles

Calculation of Plates of Different Shapes Using Generalized Equations of the Finite Difference Method

Statement of the problem. The article reviewed nonaxisymmetric tasks for calculating slabs in shape of a circle sector, wedge and a slab formed by a connection of rectangular and circular areas. The solution is based on generalized equations of the finite differences method. The algorithm allows us to take into account finite discontinuities of the desired function, the right side of the original differential equations, as well as discontinuities of derivatives of these functions without accumulation of the grid and using points outside the contour. It resolves oneself into a system of differential algebraic equations generated for field and contour points. In this paper the initial differential equations and their numerical approximation are provided. Results. Calculations of a semicircle and a wedge under different boundary conditions are presented, as well as an uncut slab in the form of a semicircle with an annular support and a composite slab are consi-dered. The solution of the above problems has been carried out on the minimum possible computational grid, comparison with the available solutions has been provided, and static checks of the calculation have been carried out. Conclusions. Along with the most common numerical method for calculating buildings and structures, it is possible and quite effective to use these equations. It is proved by means of some examples that such an approximation has a number of advantages: the results allow us to talk about the sufficient accuracy of the solution with a small number of partitions; fundamental simplicity and universality of the method.

Multicentre experience with valve-sparing aortic root replacement by means of combined remodelling and external aortic ring annuloplasty in patients with Marfan syndrome.

The most recent valve-sparing root replacement technique combines the advantages of the reimplantation (David) and remodelling (Yacoub) techniques. The aortic root is reconstructed according to the remodelling technique, the aortic valve is repaired according to the principle of effective height, and an external ring provides annular support. The purpose of this study was to evaluate operative and mid-term outcomes using this technique in patients with Marfan syndrome. Adult patients with Marfan syndrome who had an indication for aortic root surgery according to European Society of Cardiology guidelines and were operated on using this new root replacement technique were retrospectively evaluated. Follow-up was obtained from standard outpatient visits and included echocardiography. The study group comprised 22 patients (mean age 36 years, 68% males). Mean follow-up was 7.5 years. There were no mortalities. Two patients required aortic valve replacement because of aortic regurgitation. In both patients, the aortic root was severely dilated (≥65 mm) preoperatively, with grade III aortic valve regurgitation and aortic valve cusps that were very fragile. Aortic regurgitation was grade ≤I on follow-up in 18 of the remaining 20 patients. Valve-sparing root replacement using remodelling combined with aortic-ring annuloplasty is safe in patients with Marfan syndrome. The mid-term outcome is promising in patients undergoing elective valve-sparing root replacement at recommended root diameters. However, in patients with extremely dilated aortic roots and already severe aortic regurgitation, the technique should be used cautiously as aortic cusps are fragile and might not be suitable for durable repair. UMCG Research registry #11208.

ANALYSIS OF THE METHODS FOR BENDING SMALL-SIZED DISKS ON A RING SUPPORT

A number of methods for testing bending of thin discs on an annular support designed to determine the tensile strength of brittle materials, are considered. The methods differ in the type of a loading indenter (with flat, spherical, or toroidal tips), support devices, and calculation equations for determination of the breaking stress. The results of testing samples on an annular support made of two model materials which differ in the degree of brittleness, i.e., cast iron and graphite, are presented. It is shown that the calculated strength of the tested materials depends on the character of the sample destruction and on the type of bending diagram. Cast iron samples were destructed under a significant plastic deformation (characteristic bending diagram passed through the maximum), and the tensile strength of the samples corresponded to the compressive strength of the material being several times higher than the tensile strength of the material. Graphite samples underwent brittle fracture (within the linear section of the bending diagram), and the calculated strength value was comparable to the tensile strength of the material. A conclusion is made that the use of the test method of thin disk samples on an annular support for determination of the tensile strength of the material is substantiated only in the case of absolutely brittle fracture of samples with a bending diagram similar to the fracture diagram of graphite samples. Disk samples made of aluminum oxide obtained by electro-pulse sintering were tested using two methods (with flat and spherical tips). In both cases, the bending diagram of aluminum oxide samples was similar to that of graphite samples, i.e., their destruction occurred at the initial linear section of the diagram and was absolutely brittle. The results of comparative testing of the samples made of aluminum oxide, taking into account the results of testing samples made of model materials (cast iron and graphite), showed that tests on the annular support of disks using a flat-tipped indenter are the most grounded. The samples should be made of brittle materials having a linear bending diagram up to the sample destruction.

Research on Earth Excavation Technology under Annular Support of Deep Foundation Pit

Research on Earth Excavation Technology under Annular Support of Deep Foundation Pit

Valvuloplasty Without Prosthetic Ring or Band in Patients with Degenerative Mitral Regurgitation: Long-Term Results and Predictive Factors for Outcomes.

IntroductionMitral valvuloplasty including ring/band support is widely performed despite potential drawbacks of rings. Unsupported valvuloplasty is performed in only a few centers. This study aimed to report long-term outcomes of patients undergoing unsupported valvuloplasty for degenerative mitral regurgitation (MR) and to identify predictive factors for outcomes.MethodsThis is a retrospective cohort including patients undergoing mitral valve repair for degenerative MR from 2000 to 2018. The main techniques were Wooler annuloplasty and quadrangular resection. Kaplan-Meier curves and Cox regression models were used for statistical analysis.ResultsOne hundred fifty-eight patients were included (median age: 64.0 years). In-hospital mortality was 2.5%. Maximum follow-up was 19.6 years, with a median of 4.7 years (992 patient-years). Overall survival at 5, 10, and 15 years was 91.0% (95% confidence interval [CI]: 85.7-96.3), 87.6% (95% CI: 80.7-94.5), and 78.1% (95% CI: 65.9-90.3), respectively. The European System for Cardiac Operative Risk Evaluation (EuroSCORE) II was an independent predictor of late death (hazard ratio [HR] 1.42; P=0.016). Freedom from mitral reoperation at 5, 10, and 15 years was 88.1% (95% CI: 82.0-94.2), 82.4% (95% CI: 74.6-90.2), and 75.7% (95% CI: 64.1-87.3), respectively. Left atrial diameter > 56 mm was associated with late reintervention in univariate analysis (HR 1.06; P=0.049).ConclusionDegenerative MR can be successfully treated with repair techniques without annular support, thus avoiding the technical and logistical drawbacks of ring/band implantation while maintaining good long-term results. EuroSCORE II was a risk factor for late death, and larger left atrium was associated with late reoperation.

Determination of the Mechanical Properties of the Materials Produced by Electric Pulse Powder Consolidation

The field of applicability of bending of thin disks test on an annular support and the “Brazilian test” for short cylinders is discussed. These methods are used to determine the tensile strengths of the materials formed by electric pulse powder consolidation. These techniques of testing small samples make it possible to study the influence of technological factors on the strengths of the consolidated materials.

Valve sparing root replacement: an update.

Until the year 2000, the publications concerning aortic valve sparing (AVS) did not exceed 20 articles; in the following years almost 300 publications have appeared. Over 35 years from the introduction of valve sparing techniques and 500 years after the death of Leonardo da Vinci, this review highlights the significant steps in modern imaging techniques and the excellent clinical results in the field of reconstructive aortic root surgery. AVS operations underwent significant modifications over the last few years making it reproducible with satisfactory outcomes. The extraordinary potential of imaging opens new boundless horizons in the perspective of an increasingly patient-tailored surgical planning. The basic surgical concepts include the preservation and resuspension of the aortic valve in a near-normal environment (with the creation of functionally suited neo-aortic sinuses) and the re-establishment of a normal relationship of the aortic root components. Today is possible to perform a reimplantation procedure with the creation of neo-sinuses or a remodeling procedure with the addition of annular support. Both procedures can now guarantee an anatomical root reconstruction and an increased long-term durability. AVS operations have become established alternatives to Bentall procedures for patients with aortic root pathology, especially in young patients.

Comparison of two test methods for bending small disks on an annular support

Two methods of bending thin disks on an annular support are compared. The methods differ in the type of loading indenter and the equations that determine the strength of the material by the test results. The end surfaces of the indenter are flat cylindrical (indentor 1) or spherical (indentor 2). The methods were used to test identical disc samples from model materials: cast iron and graphite, as well as aluminum oxide samples obtained by spark-plasma sintering. The results of testing 24 disks of model materials and 10 disks of aluminum oxide on the ring support are presented. Bending diagrams of 12 disks of each model material on the annular support using two types of indentors indicate their different tensile strength. The calculated values of strength and their spread were higher when using indenter 2 than when using indenter 1. Thus, comparative tests have shown that the calculated strength of the tested materials depends on the nature of the failure of the samples and the type of bending diagram. The most reasonable were the test results obtained with the use of a flat-tipped indenter, which coincide with the characteristics of the strength of materials and the minimum spread of values.

Tensile strength of materials obtained by electric pulse consolidation of powders

The article investigates the possibility of determining the resistance to fracture of materials obtained from powders by electric pulse consolidation method using the test method for bending thin disks on an annular support and testing short cylinders according to the “Brazilian test”. Techniques are verified by testing small-sized thin disks and short cylinders made of gray cast iron and graphite. It is revealed a difference in the nature of the destruction of cast iron samples (plastic failure) and samples of graphite (brittle fracture). The good correspondence of the characters of destruction of graphite samples and samples produced from powders by the electric pulse consolidation is shown. The influence of various additives and manufacturing technology of materials on the resistance of the material to brittle fracture is revealed. The optimal modes of high voltage consolidation a heavy alloy based on the results of tests of short cylinders according to the “Brazilian test” scheme were obtained. The effect of the thickness of the cylinders on the strength of aluminum oxide Al2O3 is investigated.

Determination of tensile strength of brittle materials by bending thin discs on the annular support

It is proposed to use the test of bending small thin disk specimens simply supported along the contour, to determine the resistance of material to tensile strain. The results of computer analysis of stress-strain state and test a thin disk specimens made of brittle materials are cast iron and graphite as a possible model, and directly samples made by electric pulse methods are presented. It is shown the effect of size of specimens on the resistance to their destruction and different character of deformation and destruction of cast iron and graphite samples. The possibility of application of thin disc samples for the determination the resistance to tensile strain of the composite ceramics based on SiAlON with various additives Y2O3, SiC, and TiN is confirmed.

Deep circumferential annuloplasty as an adjunct to repair regurgitant bicuspid aortic valves with a dilated annulus

BackgroundFailure to address the functional aortic annulus during bicuspid aortic valve (BAV) repair has led to early repair failures. The pathology of regurgitant BAV involves annular dilatation, which is more pronounced anteriorly and deep toward the muscular interventricular septum. In this study, we assessed the results of BAV repair using a strategy of deep circumferential annular support involving the septum in patients with a dilated annulus (>26 mm) and moderate to severe aortic regurgitation (AR). MethodsBetween February 1999 and June 2015, 100 patients with regurgitant (≥2+) BAV and a dilated ventriculoaortic junction (VAJ) (≥26 mm) underwent repair with an adjunctive circumferential annuloplasty (reimplantation procedure or ring). External root dissection to accommodate the annuloplasty was carried deep onto the anterior aspect of the interventricular septum. Follow up was complete in 96 patients, with a median follow-up of 31 months and a total of 362 patient-years. Cox regression analysis was used to predict recurrence of AR. ResultsThe mean VAJ diameter was 30 ± 4 mm. Seventy-nine patients exhibited delayed prolapse of the anterior leaflet (conjoined right and left cusps in Siever type 1 or anterior cusp in Siever type 0), and 93 patients underwent reimplantation. In the entire study group, there were no in-hospital deaths, and only 1 patient had 2+ AR on discharge. There was 1 late noncardiac death. At 8 years, freedom from AR ≥2+ was 96.4% and freedom from reoperation was 96.8%. Higher preoperative AR grade, small graft size, and use of a ring were predictive of recurrent AR. ConclusionsRegurgitant BAVs with a dilated annulus display anterior cusp prolapse toward the septum. A deep circumferential annuloplasty may help maintain repair durability.

Perspective: valve sparing root repair: tips and tricks.

The remodeling and the reimplantation procedures were described more than 25years ago with the aim of sparing otherwise normal aortic valves in the presence of a root aneurysm. Important achievements in this discipline have occurred over the past decade including development and refinement of valve preserving aortic root replacement techniques, development of a classification system for aortic insufficiency, and development of surgical approaches to cusp disease with varying cusp anatomy. The main advantage of the reimplantation is the resulting annular support, and the disadvantages are the unfavorable hemodynamics and relatively longer procedural time. Conversely, the main advantages of remodeling are the physiological hemodynamics and the shorter procedural time, and the disadvantage is the lack of annular support. With technical advances and modifications, however, the differences between these two procedures have narrowed. Today preference for a reimplantation procedure is based on the perception of a better reproducibility of the surgical procedure, an increased procedural safety due to the characteristic hemostatic feature of this surgical approach, the possibility of achieving favorable hemodynamics, and a much larger amount of data present in the literature on long-term results.

Durability of Aortic Valve Cusp Repair With and Without Annular Support

To determine the value of aortic valve repair rather than replacement for valve dysfunction, we assessed late outcomes of various repair techniques in the contemporary era. From January 2001 to January 2011, aortic valve repair was planned in 1,124 patients. Techniques involved commissural figure-of-8 suspension sutures (n= 63 [6.2%]), cusp repair with commissuroplasty (n=481 [48%]), debridement (n= 174 [17%]), free-margin plication (n= 271 [27%]) or resection (n= 75) or both, or annulus repair with resuspension (n= 230 [23%]), rootreimplantation (n= 252 [25%]), or remodeling (n=35[3.5%]). Planned repair was aborted for replacement in 115 patients (10%); risk factors included greater severity of aortic regurgitation (AR; p= 0.0002) and valve calcification (p < 0.0001). In-hospital outcomes for the remaining 1,009 patients included death (12 [1.2%]), stroke (13 [1.3%]), and reoperation for valve dysfunction (14 [1.4%]). Freedom from aortic valve reoperation at 1, 5, and 10 years was 97%, 93%, and 90%, respectively. Figure-of-8 suspension sutures, valve resuspension, and root repair and replacement were least likely to require reoperation; cusp repair with commissural sutures, plication, and commissuroplasty was most likely (p < 0.05). Survival at 1, 5, and 10 years was 96%, 92%, and 83%. Immediate postoperative AR grade was none-mild (94%), moderate (5%), and severe (1%). At 10 years after repair, AR grade was none (20%), mild (33%), moderate (26%), and severe (21%). Patients undergoing root procedures were less likely to have higher-grade postoperative AR (p < 0.0001). Valve repair is effective and durable for treating aortic valve dysfunction. Greater severity of AR preoperatively is associated with higher likelihood of repair failure. Commissural figure-of-8 suspension sutures and repair with annular support have the best long-term durability.

Valve-sparing aortic root surgery. CON: remodeling.

The two major valve-sparing root replacement procedures, aortic valve reimplantation (reimplantation) and aortic root remodeling (remodeling), have advantages and disadvantages, which are reviewed herein. The main advantage of reimplantation is the resulting annular support, and the disadvantages are the unfavorable hemodynamics and relatively long procedure time. The main advantages of remodeling are the physiological hemodynamics and decreased procedure time, and the disadvantage is the lack of annular support. With technical advances and modifications, however, the differences between these two procedures have narrowed. Application of a graft with sinuses for reimplantation improves the hemodynamics, and addition of annuloplasty to remodeling provides the necessary annular support. Nevertheless, remodeling has some advantages because less root dissection is required and the procedure time is shorter and hemodynamically favorable. Thus, remodeling may be the procedure of choice for high-risk patients (such as those with acute aortic dissection, of advanced age, with reduced ventricular function, or undergoing a concomitant operation). Remodeling may also be best for young athletes because of the hemodynamic advantage. Regardless of the advantages and disadvantages, both procedures provide excellent clinical results in terms of late valve durability. Surgeons should be familiar with both techniques and properly match patients to the appropriate treatment.

The dynamic excitation of a granular chain: Contact mechanics finite element analysis and experimental validation.

There is currently interest in transmitting acoustic signals along granular chains to produce waveforms of relevance to biomedical ultrasound applications. The study of such a transduction mechanism is greatly aided by the use of validated theoretical models. In view of this, a finite element analysis is presented in this paper. The dynamics of a granular chain of six, 1 mm diameter chrome steel spherical beads, was excited at one end using a sinusoidal displacement signal at 73 kHz, and terminated by a rigid support. Output from this model was compared with the solution provided by the equivalent discrete dynamics model, and good agreement obtained. An experimental configuration involving the same chain, but terminated by an annular support made of a liquid photopolymer resin was also simulated and the velocity of the last sphere obtained through simulation was compared with laser vibrometer measurement, with good agreement. This model was then extended whereby the granular chain was coupled to an acoustic medium with the properties of water, via a thin vitreous carbon cylinder. Finite element predictions of the acoustic pressure indicate that, for a 73 kHz excitation frequency, harmonic rich acoustic pulses with harmonic content close to 1 MHz are predicted.

The choice of mitral annuloplastic ring-beyond "surgeon's preference".

Annuloplasty is a fundamental component in mitral valve repair. According to Carpentier’s original concepts, an annuloplastic ring is essential for the following three reasons: (I) to restore the size and shape of the native annulus; (II) to prevent future annular dilatation; and (III) to provide functional annular support. Logically, Carpentier designed his annuloplastic ring to remodel the annulus into the shape it takes in the systolic phase (1). Because the entire mitral valvular structure experiences the highest stress during this phase, this particular configuration may restore maximal leaflet coaptation (1). Over the past two decades, although the choice of annuloplastic ring has been the focus of extensive investigation and debate, to date it still largely remains a matter of “surgeon’s preference” rather than an evidence-based selection. In fact, only a handful of prospective randomized clinical trials had ever been conducted and existing knowledge on this particular subject is far from conclusive (2).

Study of TBM cutterhead fatigue crack propagation life based on multi-degree of freedom coupling system dynamics

Cutterhead is the core component of TBM tunneling equipment, which endures strong, multi-point distributed impact loads when the TBM tunnels, owing to the extreme surrounding rock environment of high hardness, high temperature and high quartz content. For this reason, the cutterhead works in an extremely severe vibration environment, which leads to engineering fault by a large area crack damage before the service life. Hence, the study on life prediction of TBM cutterhead under the impact loads is a core part of cutterhead design. This paper combines with the technology of system dynamics, linear elastic fracture mechanics and cumulative theory of fatigue damage, for the first time, proposes a method of fatigue crack propagation life prediction for the large and complex structures. In this paper, the TBM cutterhead of an actual project is taken as an example, to predict the fatigue crack propagation life of cutterhead piece and analyze the influences of plate thicknesses on fatigue life, then a new improved scheme of cutterhead structure is presented. The results show that the fatigue crack propagation life of actual cutterhead is 26.6km, which is able to meet the requirement of 20km service life. Moreover, the upper cover plate thickness has the greatest influence on cutterhead fatigue crack propagation life, with the thickness increasing 10%, the life increases nearly by 1.24 times. Then, the other influencing factors are as follows: thickness of the main support plate, thickness of the annular support plate and thickness of the support plate, whereas the influence of the lower cover plate thickness on fatigue life is minimal. Furthermore, the plate thickness limit sizes meeting the life requirement are obtained, and a new structure modified scheme of cutterhead is proposed. Compared with the original scheme, the new cutterhead scheme meets the requirements of structural strength and service life with 8.08% weight decrease, which achieves life determination design and lightweight design. The proposed method of fatigue crack propagation life prediction is feasible in the design and application stage of TBM cutterhead, besides, it is flexible enough and can also be applied in damage strength assessment, dynamic parameters optimization and establishment of nondestructive inspection cycle for the other large and complex structure, and takes on stronger project value and generality.

Mitral Annuloplasty Using A Biodegradable Annuloplasty Ring

With the advent of several valve repair techniques, mitral valve repair is now preferred over mitral valve replacement as the treatment of choice for several mitral pathologic conditions. Because annular dilation is a vital component in most cases of chronic mitral regurgitation (MR), annular support is necessary to provide adequate repair and optimum long-term results.1 Annular reinforcement permits shrinking of the dilated annulus, allowing adequate coaptation of the valve leaflets, thereby preventing recurrent dilation.

Study on Nondestructive Testing Method of Vertical Prestressed Reinforcement Tension in Box Girder

The diagonal cracks in the web of box girder bridge which caused by excessive loss of vertical prestressed tensioning force are particularly common. In order to effectively detect the real force of the vertical prestressed rebars. Take the exposed section of the vertical prestressed rebar as an analysis entity, and take the rebar as a rigid body; the anchoring segment is simulated by an annular outrigger and an annular elastic support. When vertical pretress tension changes, the stiffness of elastic support and the vibration frequency also change accordingly, the change of the value of tensile force can be reflected by the vibration frequency. Combined with the model test data, the nonlinear elastic parameter model between the finish .deformed rebar vertical tensioning force T and the space elastic support stiffness K is established. The validity of the method was checked by extension test. The study indicate that this method is accurate, fast and convenient for engineering applications, can effectively improve the construction quality.

Cirugía reparadora de la insuficiencia aórtica

IntroductionWe present our initial experience with isolated aortic valve repair or remodeling operation (Yacoub) in patients with aortic root dilatation. Short and mid-term follow-up data are reported. MethodsFrom 2009 to 2011, 25 patients underwent surgery. Yacoub remodeling surgery was carried out in 9 cases with root dilatation: anuloaortic ectasia in 8 cases, Beals Syndrome in one case. Coroneo® ring was implanted in 6 of these and subaortic Schäfers suture in 3. In the 16 cases isolated valve insufficency was the only pathology found (4 bicuspid cases). Echocardiogram was also carried out in the immediate postoperative period as well as one, six, 12 and 24 months after surgery. ResultsHospital mortality was 4% (1/25). Mean age was 44. Mean ischemic time was 54minutes for isolated valve repair and 139minutes for aortic root remodeling. Two patients were reoperated upon due to severe aortic regurgitation. Control echocardiograms showed satisfactory repair in 21 cases with minimum residual insufficiency and moderate regurgitation in 2 cases. ConclusionsOur technique of choice for aortic valve repair is the central plication being an intuitive and reproducible technique. In aortic regurgitation associated with aortic root dilatation the technique of choice is the Yacoub remodeling with Coroneo® ring, providing lasting annular support.