1,501 research outputs found

    Stress-strain analysis of aortic aneurysms

    Get PDF
    Tato práce se zabývá problematikou aneurysmat břišní aorty a možností využít konečnoprvkovou deformačně-napěťovou analýzu těchto aneurysmat ke stanovení rizika ruptury. První část práce je věnována úvodu do problematiky, popisu kardiovaskulární soustavy člověka s důrazem na abdominální aortu, anatomii, fyziologii a patologii stěny tepny s důrazem na procesy vedoucí ke vzniku aneurysmatu. Dále se práce věnuje rizikovým faktorům přispívajících ke vzniku aneurysmat spolu s analýzou současných klinických postupů ke stanovení rizika ruptury spolu se srovnáním navrhovaného kritéria maximálního napětí. Dominantní část této disertace je věnována identifikaci faktorů ovlivňujících napjatost a deformaci stěny aneurysmatu spolu s návrhem nových postupů, prezentací vlastních poznatků vedoucích ke zpřesnění určení rizika ruptury pomocí deformačně- napěťové analýzy a metody konečných prvků. Nejprve je analyzován vliv geometrie, vedoucí k závěru, že je nezbytné používání individuálních geometrií pacienta. Dále je pozornost zaměřena na odbočující tepny, které ve stěně působí jako koncentrátor napětí a mohou tedy ovlivňovat napjatost v ní. Jako další podstatný faktor byl identifikován vliv nezatížené geometrie a bylo napsáno makro pro její nalezení, které bylo opět zahrnuto jako standardní součást do výpočtového modelu. Mechanické vlastnosti jak stěny aneurysmatu, tak intraluminálního trombu jsou experimentálně testovány pomocí dvouosých zkoušek. Také je zde analyzován vliv modelu materiálu, kde je ukázáno, že srovnávání maximálních napětí u jednotlivých modelů materiálu není vhodné díky zcela rozdílným gradientům napětí ve stěně aneurysmatu. Dále je zdůrazněna potřeba znalosti distribuce kolagenních vláken ve stěně a navržen program k jejímu získání. Intraluminální trombus je analyzován ve dvou souvislostech. Jednak je ukázán vliv jeho ruptury na napětí ve stěně a jednak je analyzován vliv jeho poroelastické struktury na totéž. Posledním identifikovaným podstatným faktorem je zbytková napjatost ve stěně. Její významnost je demonstrována na několika aneurysmatech a i tato je zahrnuta jako integrální součást do našeho výpočtového modelu.Na závěr jsou pak navrženy další možné směry výzkumu.This thesis deals with abdominal aortic aneurysms and the possibility of using finite element method in assessment of their rupture risk. First part of the thesis is dedicated to an introduction into the problem, description of human cardiovascular system where the abdominal aorta, its anatomy, physiology and pathology is emphasized. There Processes leading to formationing of abdominal aortic aneurysms are also discussed. Risk factors contributing to creation of aneurysms are discussed next. Finally, an analysis of current clinical criteria which determine rupture risk of an abdominal aortic aneurysm is presented and compared with the new maximum stress criterion being currently in development. Main part of the thesis deals with the identification of relevant factors which affect stress and deformation of aneurysmal wall. This is connected with proposals of new approaches leading to predicting the rupture risk more accurately by using finite element stress-strain analysis. The impact of geometry is analyzed first with the conclusion that patient-specific geometry is a crucial input in the computational model. Therefore its routine reconstruction has been managed. Attention is then paid to the branching arteries which were neglected so far although they cause a stress concentration in arterial wall. The necessity of knowing the unloaded geometry of aneurysm is then emphasized. Therefore a macro has been written in order to be able to find the unloaded geometry for any patient-specific geometry of aneurysm. Mechanical properties of both aneurysmal wall and intraluminal thrombus were also experimentally tested and their results were fitted by an isotropic material model. The effect of the material model itself has been also investigated by comparing whole stress fields of several aneurysms. It has been shown that different models predict completely different stresses due to different stress gradients in the aneurysmal wall. The necessity of known collagen fiber distribution in arterial wall is also emphasized. A special program is then presented enabling us to obtain this information. Effect of intraluminal thrombus on the computed wall stress is analyzed in two perspectives. First the effect of its failure on wall stress is shown and also the impact of its poroelastic structure is analyzed. Finally the residual stresses were identified as an important factor influencing the computed wall stress in aneurysmal wall and they were included into patient-specific finite element analysis of aneurysms. Further possible regions of investigation are mentioned as the last part of the thesis.

    "Keep Your Head Down": Unprotected Migrants in South Africa

    Get PDF
    Looks at the experiences of undocumented migrant farm workers in South Africa, many of whom lack adequate legal protections and are particularly vulnerable to human rights abuses when they are arrested, detained, or deported

    ERISA Health Plan Liability: Issues and Options for Reform

    Get PDF
    This background paper was written as congressional conferees faced the task of resolving differences between patient protection bills by the U.S. House of Representatives and U.S. Senate in late 1999. In order to discuss the principal issues facing policymakers and options for reform, it begins by describing problems raised by the federal law governing private-sector employee health plans (the Employee Retirement Income Security Act of 1974) from a consumer perspective. It then discusses approaches proposed by the Clinton administration and the House and Senate to give consumers greater ability to challenge health plan coverage decisions, focusing in particular on issues that would arise if Congress decided to give health plan participants increased ability to sue for damages under state laws. The paper then explores, from the perspectives of physicians, employers, and insurers, employee health plan liability in areas such as negotiating the terms of contracts, improving the general quality of medical care, assigning liability for medical errors and coverage denials, and determining who has the power to decide which procedures and technologies are medically necessary. Finally, possible approaches to liability — ranging from contract law to tort law notions of liability — are presented in the context of the bills passed by the House and Senate in 1999

    A Chicken (Nugget?) in Every Pot: What\u27s at Stake in the Budget Debate

    Get PDF
    This paper explores various aspects of the 1999 budget debate fueled in large part by federal agencies\u27 projection of a 2.9trillionsurplusover10years.Thetaxbill,whichwouldprovideabout2.9 trillion surplus over 10 years. The tax bill, which would provide about 400 billion in tax relief, is also discussed; special attention is given to the health care provisions of this legislation

    ERISA Health Plan Denials: Exploring Models for External Review

    Get PDF
    This paper outlines the current process under the Employee Retirement Income and Security Act (ERISA) by which plan participants can appeal a claim denial as well as changes to the claims procedure requirements being considered by the Department of Labor. It describes state legislative activity in this area and summarizes research describing practices currently in place among managed health care organization. The paper also describes two existing models for external review of managed care plan decisions, one used by the Medicare program and another by the state of Florida

    Emerging Issues in the Use of Binding Arbitration to Resolve Disputes between Individuals and Health Plans

    Get PDF
    After briefly describing the federal legal framework fostering the growth of binding arbitration, this paper identifies controversies surrounding arbitration as well as arguments supporting and opposing its use. The paper describes the use of arbitration among certain types of collectively bargained employee health plans regulated under the Employee Retirement Income Security Act of 1974 (ERISA), by health maintenance organizations (HMOs) in California, and by a large employer operating a self-insured ERISA health plan. Evidence cited by the California Supreme Court that the largest HMO in California operated its mandatory arbitration program in an unfair way is presented, along with the HMO\u27s subsequent efforts to identify problems with its arbitration program and correct them. Proposals introduced in the California legislature to further regulate arbitration or to ban predispute arbitration agreements with health plans are described as well as their possible preemption by federal law. A protocol developed by leading associations involved in alternative dispute resolution, law, and medicine is also described. After describing the treatment of arbitration by proposed laws and regulations under consideration by Congress and the U.S. Department of Labor for employee health plans, the paper concludes by raising some of the federal policy issues presented by arbitration

    Media freedom: a view from the East

    Get PDF
    In the latest of our guest blogs, London College of Communications student Lydia Polzer, who was born in the old DDR or East Germany, reflects on how many people in the former Communist countries are disappointed with the ‘freedoms’ offered by the western liberal news media. This article was also the winner for a UNESCO essay competition which set the question: “The greatest threat to media freedom in the world is…” This is Lydia’s view

    HIPAA as a Regulatory Model: Early Experiences and Future Prospects

    Get PDF
    In the context of the debate over bolstering consumer protection in health care without imposing excessive costs or onerous regulatory requirements, this paper examines the Health Insurance Portability and Accountability Act of 1996 (HIPAA) as a regulatory model. The paper reviews the provisions of the legislation, examines the roles of the Department of Labor and the Health Care Financing Administration in implementing HIPAA, raises issues surrounding implementation and enforcement, and examines the usefulness of the HIPAA model as a vehicle for applying consumer protection measures

    The Federal Employees Health Benefits Program: What Lessons Can It Offer Policymakers?

    Get PDF
    This paper provides an historical overview of the Federal Employees Health Benefits (FEHB) program and its marketplace dynamics. It also reviews key program features and issues, including payments to health plans, strategies used to mitigate the opportunities for risk selection, and costs
    corecore