The very existence of several methods (6, 13, 16, 20, 26, 41) to analyze left ventricular wall motion from contrast angiograms indicates that no exact, generally accepted procedure is available to track fixed points along the endocardial wall. In animals, specific sites of the endocardium can easily be followed with endocardially implanted metal clips (5, 32, 44) and roentgen cinematography. For obvious reasons, endocardial markers have not been inserted in humans, although midwall motion (9) and epicardial wall motion (3, 15, 31) have been studied in human hearts with surgically implanted metal markers. However, major differences exist in extent and direction of movements of neighboring endocardial, midwall and epicardial sites as the wall thickens (44, 64). Therefore, none of these methods can provide an accurate description of endocardial wall motion. Recently, we described and evaluated a method to assess left ventricular endocardial wall motion in humans from the pathways of anatomic landmarks recognizable on the endocardial border. For delineation of the endocardial border in the contrast angiogram, an automated high resolution outlining system (60) was employed. In the detected left ventricular contour, small landmarks are available that can be followed throughout the cardiac cycle by analysis of consecutive frames of the cineangiogram. The hypothesis that these landmarks represent specific anatomic sites has been validated by placing minute "harpoons" in the endocardium of piglets.
The axial behaviour and design of hot-finished high strength steel tubular elements with internal prestressing cables, representing the chord members in prestressed trusses, are examined in this paper. A comprehensive programme of experiments and numerical modelling was performed, the results of which were combined to develop resistance expressions for the design of prestressed high strength steel members. A total of 12 tensile and 10 compressive member tests were carried out, with the key variables examined being the steel grade (S460 and S690), the initial prestress level and the presence of grout. Numerical models were developed to replicate the structural response of the compressive member tests and subsequently used to generate parametric results, where the member slenderness, size of prestressing cable, applied prestress level, steel grade (S460 or S690), and grout condition (grouted and non-grouted), were varied. The presence of cables was shown to enhance the tensile capacity of the members, while the addition of prestress resulted in extended elastic range. In compression, the effect of prestress was detrimental, and a modified Perry-Robertson method, developed in [1], was extended to hot-finished high strength steel members.
Kink banding, common to many structures in nature and engineering, has several distinctive features---notably highly nonlinear snap-back instability leading to localization and sequential lock-up. The proposed friction model, although simplified, introduces these defining characteristics without obscuring them by including other effects of lesser immediate significance. In the absence of small imperfections or disturbances, linearized theory suggests that in its pre-kinked configuration the system never goes unstable. However, under sufficient applied end-displacement it is shown to be in a state of extreme metastability, such that micro-disturbances would trigger the nonlinear response. To overcome this problem we adopt an energy approach based on a global rather than a local stability criterion. When applied to imperfect systems with small initial misalignments, the critical displacement thus defined shows little of the sensitivity expected from other stability criteria, and provides a useful lower bound on the expected critical displacement and associated load. We offer the frictional model not as a complete description, but as a prototype to which other components can be added. Thus it provides information on the triggering, localization and lock-up processes, for example, but not on the choice of kink band width which is fixed a priori. Suggestions are provided throughout of extra energy contributions which will extend the model's capability.
<p>Wire arc additive manufacturing (WAAM), a novel technology enabling the manufacturing of large- scale metallic components, shows particular suitability for the construction sector. To explore the potential of the current technology, a pedestrian steel bridge with a span of 4 m, optimised using topology and sizing optimisation, was manufactured using WAAM, making it the world's first topologically optimised additively manufactured steel bridge. A non-destructive test of the bridge was carried out under ULS load levels. The performance of the bridge during the tests was monitored using digital image correlation (DIC) as well as using analog sensors. The test results showed very good correlation with the predictions from the FE models established during the design of the bridge, and the bridge successfully passed the non-destructive load test.</p>
Advances in additive manufacturing are increasingly allowing bespoke, carefully designed, metamaterial lattice structures to be constructed for enhanced mechanical performance. For instance, in structural elements that are designed to absorb energy and shield a more valuable structure, the properties combining a high initial stiffness followed by a practically zero underlying stiffness, ensure that a desired energy quantity may be absorbed within a limited displacement and that any stress transfer to the valuable structure is minimized. Presently, a lattice structure is studied that is deliberately designed to switch locally under compression between conventional material behaviour to that exhibiting auxetic (negative Poisson’s ratio) behaviour through a sequence of snap-through instabilities within layers of individual lattice cells. The sequence of buckling instabilities can potentially be controlled to maintain the loading level alongside the low structural stiffness while the required energy quantity is absorbed, without necessarily damaging the material in the process. This departs from the usual paradigm where such structures are presently designed to be sacrificial and opens up the intriguing possibility of introducing such structural elements that are repairable and therefore reusable.
Receptor mediated hydrolysis of phos- phatidylinostol 4,5-bisphosphate is now regarded as an important step in the regulation of intracellular calcium and ASM contraction.Lithium (Li +), a potent inhibitor of inositol-l-phosphatase, depletes cellular inositol and has been shown to modulate ASM contraction in vitro (Menkes et al, Am Rev Respir Dis 1988;33:A1 15).We have therefore examined the effects ofLi + on musarinic receptor stimulated inositol polyphosphate (InsPl-InsP4) formation in bovine trachealis.Muscle slices (300 x 300 pm) were labelled with[3H]myo-inositol (NEN; 2 5 pCi/50 p1 slices) prior to stimula- tion with 01 mM carbachol for 30 min in the presence or absence of Li+.Reactions were terminated with 1M TCA and Inspl-InsP4 separated by anion exchange chromatogra- phy.Li + caused a dose dependent increase in [3H] InsPl accumulation (10-7 (1-3) fold increase (mean (SEM)); EC50 1-7 mM). 5 mM Li + increased [3H] InsP 2, [3H] InsP3 and [3H] InsP4 levels by 2-1 (01), 1-2 (01) and 0-98 (04) fold respectively.The inhibition of [3H] InsP2 breakdown by Li + was less potent than for [3H] InsPl.The effect of Li + on [3H] InsP3 accumulation may reflect the marked predominance of the Ins (1, 3, 4)P3 isomer over Ins (1, 4, 5)P3 seen in this tissue following carbachol stimulation since the conversion of Ins (1, 3, 4)P3 to Ins (3, 4)P2 is also Li+ sensitive.This study indicates that low concentrations of Li + severely perturb carbachol stimulated inositol polyphosphate metabolism in ASM.These findings, together with the depletion in phos- phatidylinositol seen following carbachol stimulation in the presence of Li + (Chilvers et al, Br J Pharmac: 1988;95:778P), may form the biochemical basis for the effect of lithium on ASM contractility.Tolerance to metabisulphite induced bronchoconstriction and duration of action of nedocromil sodium
Restoration of coronary blood flow following successful bypass surgery would be expected to lead to improvement of regional contraction. Several methods have been described for the quantitative assessment of regional or segmental left ventricular wall motion from the left ventriculogram. All methods need a reference point as a basis for their coordinate systems or to compensate for movement of the patient relative to the film camera. Morphological abnormalities such as aneurysms or akinetic areas influence the location of the reference point, resulting in artifacts when measuring wall motion. Localized abnormalities of contraction are not always reflected in "overall" measurements. Akinesis and/or dyskinesis of one or more segments can occur in the presence of normal end diastolic volume or ejection fraction. Such overall parameters will, however, gradually go into pathological ranges with an increase in the number of abnormally contracting segments. Another approach to the quantification of local wall motion uses radiopaque markers. In this study marker pairs are implanted during bypass surgery in the area of newly perfused regions as well as in control regions. Sequential cineradiograms at 50 fr. per second were made at intervals over a period of one year. It was found that direct traumatic effects of the surgical intervention overwhelm the expected improvement of myocardial function in the first three postoperative months. At present the quantitative approach to segmental cardiac function is mainly one of image analysis in one or two preselected planes. Subjective visual interpretation of these images should be replaced by objective data analysis.
The coronary stent has been investigated as an adjunct to percutaneous transluminal coronary angioplasty to obviate the problems of early occlusion and late restenosis. From March 1986 to March 1990, 265 patients (308 lesions) were implanted with the coronary Wallstent® in 6 European centers. For this study, the patients were analyzed according to date of implantation (group 1, March 1986 to January 1988; group 2, February 1988 to March 1990) and vessel type (native arteries versus bypass grafts). Quantitative angiographic follow-up was performed in 82% of the study patients. The early in-hospital occlusion rate in the overall group was 15%. Group 1 patients had a 20% rate in contrast to 12% rate in group 2 (p = not significant [NS]). The early occlusion rate in native vessels and bypass grafts was 19 and 8%, respectively (p = 0.019). Restenosis was determined by 2 criteria (criterion 1, ≥0.72 mm loss in minimal luminal diameter from poststent to follow-up; criterion 2, ≥50% diameter stenosis at follow-up) within the stent and in the segments immediately proximal and distal to the stent. The restenosis rate with criterion 1 was 43% in the overall group of patients, 35% in group 1 versus 49% in group 2 (p = NS), and 34% in native vessels versus 54% in bypass grafts (p = 0.016). The second criterion was met by 27% of patients in the overall group, 21% in group 1 versus 32% in group 2 (p = NS), and 18% in native vessel versus 39% in bypass grafts (p = 0.005). The overall mortality during the study period was 6.6% in native arteries and 9% in bypass grafts (6 and 7.9% at 1 year, respectively). The actuarial event-free survival (freedom from death, myocardial infarction, bypass surgery or angioplasty) for native artery patients was 46% at 40 months and for bypass graft patients 37% at 20 months. It is concluded that early in-hospital occlusions remain a major problem with this device despite improvement in the later experience. Although patients with bypass grafts had a significantly lower early occlusion rate than those with implantation of native arteries, a significantly higher rate of late restenosis limited the early benefits of stenting. The indications for stenting remain unknown and require results of randomized clinical studies.
