Impact of Stent-Graft Oversizing on the Thoracic Aorta: Experimental Study in a Porcine Model

Purpose: To analyze in an experimental animal model the effect of 4 different levels of stents-graft oversizing on non-atherosclerotic aortas such as those found in young individuals who undergo stent-graft repair for traumatic aortic injuries. Methods: The diameter of the porcine thoracic aorta is similar to the aorta of young adults (18-20 mm), so 25 pigs were randomized into 5 groups: 1 control (without stent-graft) and 4 oversizing groups (A: 10%-19%, B: 20%-29%, C: 30%-39%, and D: >40%). Two types of biomechanical tests were performed on all aortas 4 weeks after endoprosthesis deployment. Results: The results of the detachment test, which analyzed the strength necessary to remove the stent-graft from the aorta, were similar in the 4 groups (A: 42 N, B: 41 N, C: 46 N, and D: 46 N). However, 2 aortas ruptured during the tests (groups C and D). The second test was performed in 3 aortic segments. Maximum shear strength, maximum stress, and maximum tension supported by the aortic wall had a negative and linear correlation with oversizing. There were significant differences in all 4 groups when compared with the control group. Strain, which reflects the elastic properties of the aortic wall, was very similar in all 4 groups, but a great difference was found when compared with the control group (p<0.0001). Conclusion: The study showed an important subacute change in the biomechanical properties of the aortic wall after implantation of an oversized endoprosthesis. This weakness of the aortic wall was confirmed by 2 ruptures during the detachment test. These results partially explain the interaction of stent-grafts with non-atherosclerotic thoracic aortas and may serve as a basis for further studies and the development of specific material to be used in vascular trauma and young patients. J Endovasc Ther. 2011; 18: 576-584

Fluid dynamics simulation of right ventricular outflow tract oversizing.

OBJECTIVES: Repair of the right ventricular outflow tract (RVOT) in paediatric cardiac surgery remains challenging due to the high reoperation rate. Intimal hyperplasia and consequent arteriosclerosis is one of the most important limitation factors for graft durability. Since local shear stress and pressure are predictive elements for intimal hyperplasia and wall degeneration, we sought to determine in an oversized 12-mm RVOT model, with computed fluid dynamics simulation, the local haemodynamical factors that may explain intimal hyperplasia. This was done with the aim of identifying the optimal degree of oversizing for a 12-mm native RVOT. METHODS: Twenty domestic pigs, with a weight of 24.6 ± 0.89 kg and a native RVOT diameter of 12 ± 1.7 mm, had valve conduits of 12, 16, 18 and 20 mm implanted. Pressure and flow were measured at 75, 100 and 125% of normal flow at RVOT at the pulmonary artery, pulmonary artery bifurcation and at the left and right pulmonary arteries. Three-dimensional computed fluid dynamics (CFD) simulation in all four geometries in all flow modalities was performed. Local shear stress and pressure conditions were investigated. RESULTS: Corresponding to 75, 100 and 125% of steady-state flow, three inlet velocity profiles were obtained, 0.2, 0.29 and 0.36 m/s, respectively. At inflow velocity profiles, low shear stress areas, ranged from 0 to 2 Pa, combined with high-pressure areas ranging from 11.5 to 12.1 mmHg that were found at distal anastomosis, at bifurcation and at the ostia of the left and right pulmonary arteries in all geometries. CONCLUSIONS: In all three oversized geometries, the local reparation of shear stress and pressure in the 16-mm model showed a similar local profile as in the native 12 mm RVOT. According to these findings, we suggest oversizing the natural 12-mm RVOT by not more than 4 mm. The elements responsible for wall degeneration and intimal hyperplasia remain very similar to the conditions present in native RVOT.

Oversizing and Restenosis with Self-Expanding Stents in Iliofemoral Arteries

Uncoated self-expanding nitinol stents (NS) are commonly oversized in peripheral arteries. In current practice, 1-mm oversizing is recommended. Yet, oversizing of NS may be associated with increased restenosis. To provide further evidence, NS were implanted in porcine iliofemoral arteries with a stent-to-artery-ratio between 1.0 and 2.3. Besides conventional uncoated NS, a novel self-expanding NS with an antiproliferative titanium-nitride-oxide (TiNOX) coating was tested for safety and efficacy.

Nitinol Stent Oversizing in Patients Undergoing Popliteal Artery Revascularization: A Finite Element Study

Nitinol stent oversizing is frequently performed in peripheral arteries to ensure a desirable lumen gain. However, the clinical effect of mis-sizing remains controversial. The goal of this study was to provide a better understanding of the structural and hemodynamic effects of Nitinol stent oversizing. Five patient-specific numerical models of non-calcified popliteal arteries were developed to simulate the deployment of Nitinol stents with oversizing ratios ranging from 1.1 to 1.8. In addition to arterial biomechanics, computational fluid dynamics methods were adopted to simulate the physiological blood flow inside the stented arteries. Results showed that stent oversizing led to a limited increase in the acute lumen gain, albeit at the cost of a significant increase in arterial wall stresses. Furthermore, localized areas affected by low Wall Shear Stress increased with higher oversizing ratios. Stents were also negatively impacted by the procedure as their fatigue safety factors gradually decreased with oversizing. These adverse effects to both the artery walls and stents may create circumstances for restenosis. Although the ideal oversizing ratio is stent-specific, this study showed that Nitinol stent oversizing has a very small impact on the immediate lumen gain, which contradicts the clinical motivations of the procedure.

Avaliação e optimização operacional: estudo do terminal de contentores de Alcântara

Trabalho Final de Mestrado para obtenção do grau de Mestre em Engenharia Mecânica - Ramo Manutenção e Produção

Caraterização do acesso ao Centro Hospitalar Lisboa Norte, EPE : análise do acesso e da utilização da consulta externa e da urgência do Centro Hospitalar Lisboa Norte, EPE

RESUMO - Introdução: As alterações verificadas no dimensionamento e na redistribuição da rede de prestação de cuidados hospitalares, nomeadamente no que confere à reorganização das áreas de influência, e, cumulativamente, à abertura do Hospital Beatriz Ângelo, tornam evidente a necessidade de se analisar o acesso e a utilização da consulta externa e da urgência, antes e depois destas alterações. Objetivo: Este trabalho de investigação tem como principal objetivo analisar o acesso e a utilização da consulta externa e da urgência do Centro Hospitalar Lisboa Norte e verificar a evolução desse mesmo acesso, no período de 2010 a 2013. Material e Métodos: Estudo descritivo que visa determinar a frequência e a distribuição dos episódios de Consulta Externa e de Urgência do Centro Hospitalar Lisboa Norte. Foram considerados todos os episódios de consulta externa (3785579 episódios) e de urgência (1140052 episódios) ocorridos entre 1 de janeiro de 2010 e 31 de dezembro de 2013. Resultados: Entre 2010 e 2013, verificou-se o aumento de +2,3% no número de primeiras consultas e de +5%, em consultas subsequentes. As especialidades médicas com maior afluência são Oftalmologia, Dermatologia I, Pediatria e Otorrinolaringologia I. Observou-se, no total de consultas, qual a percentagem que, em cada ano, obteve um tempo de espera inferior a 1 mês, entre a marcação e a realização da consulta: 56,7%, em 2010; 54,3%, em 2011; 55% em 2012; 56,2%, em 2013. Verificou-se o decréscimo do número de atendimentos de urgência, no período em análise, de -38,9%. Cerca de 90% dos atendimentos de urgência respeitam a utentes que acorrem diretamente à urgência sem virem referenciados de outras unidades de saúde. Os meses de janeiro e fevereiro são aqueles que registam maior afluência, 9,9% e 8,8%, respetivamente. O período de maior afluência regista-se entre as 9 e as 11 horas, representando 20,7% dos episódios, em 2010, 21,2%, em 2011, 21% e 20,5%, em 2012 e 2013, respetivamente. Conclusão: Face à alteração da área de influência do Centro Hospitalar Lisboa Norte, torna-se necessária a adaptação da capacidade instalada para haja um sobredimensionamento face à procura, bem como a adequação de recursos internos, financeiros, humanos e tecnológicos.

The GraftConnector experience. Long-term patency and histological work up in an animal model.

BACKGROUND: A device to perform sutureless end-to-side coronary artery anastomosis has been developed by means of stent technology (GraftConnector). The present study assesses the long-term quality of the GraftConnector anastomosis in a sheep model. METHODS: In 8 adult sheep, 40-55 kg in weight, through left anterior thoracotomy, the right internal mammary artery (RIMA) was prepared and connected to the left anterior descending artery (LAD) by means of GraftConnector, on beating heart, without using any stabilizer. Ticlopidine 250 mg/day for anticoagulation for 4 weeks and Aspirin 100 mg/day for 6 months were given. The animals were sacrificed after 6 months and histological examination of anastomoses was carried out after slicing with the connector in situ for morphological analysis. RESULTS: All animals survived at 6 months. All anastomoses were patent and mean luminal width at histology was 1.8 +/- 0.2 mm; mean myotomia hyperplasia thickness was 0.21 +/- 0.1 mm. CONCLUSIONS: Long-term results demonstrate that OPCABGs performed with GraftConnector had 100% patency rate. The mean anastomotic luminal width corresponds to mean LAD's adult sheep diameter. We may speculate that myotomia hyperplasia occurred as a result of local device oversizing.

Aortic root rupture: implications of catheter-guided aortic valve replacement.

PURPOSE OF REVIEW: The safety and efficiency of trans catheter aortic valve implantation (TAVI) has been clearly demonstrated. In high-risk patients, the number of procedures is constantly increasing and in western European countries this procedure is employed in more than 30% of isolated aortic valve replacements. The literature, however, focusing on perioperative aortic root (AoR) rupture is rather limited to just a few reports. The aim of this review is to analyze the pathophysiology of AoR rupture during TAVI, stressing the implications of the morphology of the AoR for this devastating complication. RECENT FINDINGS: Currently, perioperative AoR rupture ranges between 0.5 and 1.5% during TAVI, with almost 100% mortality. Recently, valve oversizing and balloon dilatation in a calcified and small AoR were considered as the most important predictive factors for this complication. SUMMARY: The most fragile unit of the AoR is its anchoring substrate to the ostium of the left ventricle. This membranous structure is not involved in the degenerative process leading to aortic valve stenosis. Due to the TAVI and/or balloon dilatation of the calcium stationed on the three leaflets and their attachment, a lesion may result on this structure. And, as a consequence, there is rupture of the AoR.

Tuoreen sahatavaran mittavaihtelujen vaikutus sahauksen kannattavuuteen

Työn tavoitteena oli esittää tuoreen sahatavaran mittahajonnan merkitys sahaukselle. Lisäksi tutkittiin eri vuodenaikojen vaikutusta märkämitan hajontaan. Tutkimuksessa selvitettiin myös sahatavaran kuivauksen aikaisen kutistuman suuruutta ja hajontaa eri tilanteissa. Tutkimuksessa suoritettiin mittauksia kolmella eri sahalla n. 12 kk:n ajan. Näin saatiin tietoa eri vuodenaikojen vaikutuksesta märkämittojen hajontaan, ja sitä kautta sahauksen kannattavuuteen. Kuivauksen vaikutusta tuoremittojen ohjaukseen tutkittiin mittaamalla useita eri koe-eriä ennen ja jälkeen kuivauksen. Mittaustietojen avulla pystytään määrittämään todellinen tarvittava märkämitta, ja vältetään turhaa ylimittaa sahauksessa Tutkimus osoitti vuodenaikojen selvän merkityksen sahaushajontaan. Kuivauksen vaikutuksesta kappaleiden hajontaan saatiin tutkimuspohjaista, tarkkaa tietoa. Myös todellisesta kuivauskutistuman suuruudesta saatiin selkeä käsitys, joka helpottaa märkämitan, ja siten myös asiakkaalle menevän, todellisen sahatavaramitan määrittelyä.

Analisis de los alcances y limitaciones de la estructura policial de Colombia en materia de seguridad nacional

En la Policía Nacional de Colombia, al pasar de los años, se han vislumbrado dificultades de adecuación entre las autoridades de policía y las autoridades militares, que se manifiestan en duplicidad de funciones y organismos. La desarticulación entre las actuaciones policiales y militares ha hecho que esta institución históricamente haya venido adoptando un doble carácter militar y civil, dadas las condiciones de un conflicto permanente en el país. La policia nacional de colombia en su estructura funcional en su interior demuestra una sobredimensión en sus funciones, ya sea por el conflicto interno o la serie de reformas que el estado ha hecho a esta institución, en el cual se opta por un carácter nacional y no ciudadano, haciendo que en algunos casos este sobre empoderamiento genere algunas dificultades a la hora de cumplir sus funciones fundamentales segun su filosofia.

Design and assessment of a large commercial Photovoltaic System in Barbados

One of the main aims of this thesis is to design an optimized commercial Photovoltaic (PV) system in Barbados from several variables such as racking type, module type and inverter type based on practicality, technical performance as well as financial returns to the client. Detailed simulations are done in PVSYST and financial models are used to compare different systems and their viability. Once the preeminent system is determined from a financial and performance perspective a detailed design is done using PVSYST and AutoCAD to design the most optimal PV system for the customer. In doing so, suitable engineering drawings are generated which are detailed enough for construction of the system. Detailed cost with quotes from relevant manufacturers, suppliers and estimators become instrumental in determining Balance of System Costs in addition to total project cost. The final simulated system is suggested with a PV capacity of 425kW and an inverter output of 300kW resulting in an array oversizing of 1.42. The PV system has a weighted Performance Ratio of 77 %, a specific yield of 1467 kWh/kWp and a projected annual production of 624 MWh/yr. This system is estimated to offset approximately 28 % of Carlton’s electrical load annually. Over the course of 20 years the PV system is projected to produce electricity at a cost of $0.201USD/kWh which is significantly lower than the $0.35 USD/kWh paid to the utility at the time of writing this thesis. Due to the high cost of electricity on the island, an attractive Feed-In-Tariff is not necessary to warrant the installation of a commercial System which over a lifetime which produces electricity at less than 60% of the cost to the user purchasing electricity from the utility. A simple payback period of 5.4 years, a return on investment of 17 % without incentives, in addition to an estimated diversion of 6840 barrels of oil or 2168 tonnes of CO2 further provides compelling justification for the installation of a commercial Photovoltaic System not only on Carlton A-1 Supermarket, but also island wide as well as regionally where most electricity supplies are from imported fossil fuels.