Comportamiento mecánico de la aorta ascendente : caracterización experimental y simulación numérica

Resumen En este trabajo se realiza una caracterización experimental y numérica del comportamiento mecánico de la pared de la aorta humana. Se destaca la importancia de este tema debido al creciente interés en conocer las propiedades y la respuesta mecánica de los vasos sanguíneos por su aplicación en el tratamiento y diagnóstico de las enfermedades cardiovasculares. En el presente trabajo se introducen algunos aspectos de los tejidos arteriales y características generales de las patologías más frecuentes en la aorta. Además se incluye una recopilación breve del estado del arte sobre el comportamiento mecánico de estos vasos. También se describen los modelos constitutivos de comportamiento no lineal (con grandes deformaciones) e hiperelásticos utilizados para la simulación numérica de la pared arterial, en una formulación implementable en un programa de elementos finitos. Se han realizado una serie de experimentos para caracterizar la respuesta mecánica de vasos arteriales. Se llevaron a cabo ensayos de tracción, presurización, medición del ángulo de apertura e histología en paredes de aorta con diferentes antecedentes clínicos. Mediante los ensayos se ajustaron los parámetros de los modelos constitutivos y se obtuvieron otros parámetros mecánicos de interés, como las tensiones y deformaciones de rotura. Con ellos se ha cuantificado el efecto de la patología y la edad en la respuesta mecánica de este tipo de tejidos. Empleando los modelos ajustados en los ensayos de tracción uniaxial se ha realizado la simulación de diversos ensayos de presurización, validándose con las mediciones efectuadas en este mismo trabajo. Finalmente, también se ha llevado a cabo el análisis numérico de un cayado aórtico en condiciones de funcionamiento fisiológico normales, de hipertensión o en condiciones más severas provocadas por un trauma o accidente. VII Abstract This thesis shows an experimental and numerical characterization of the mechanical behaviour of the human aortic wall. This subject is of paramount importance due to the increasing interest in the mechanical properties and response of blood vessels, in order to improve the treatment and diagnose of cardiovascular diseases. In the present work, some aspects of arterial tissues are presented and the general characteristics of the aorta’s most common pathologies are discussed. In addition, a brief summary of the state of the art on the mechanical behaviour of these vessels is included. A series of experiments have been done in order to characterize the mechanical response of the blood vessels. Four different types of experiments were performed on samples of human aorta with different clinical histories: uniaxial tensile tests, pressurization tests, measurement of the opening angle and histology. The parameters of some constitutive models were obtained adjusting their response to the experimental data from the uniaxial tests. Other mechanical parameters such as strength and deformation at rupture were also obtained. In order to simulate numerically the arterial wall response, two constitutive models with nonlinear (with large deformations) and hyperelastic behaviour, in the context of the continuum mechanics, are described. These formulations have been implemented in a finite element code. Pressurization tests have been simulated using the constitutive models previously tunned with the uniaxial tensile tests. The accuracy of these simulations was checked with the experimental data obtained in this thesis. Finally, numerical analyses of the mechanical response of an aortic arch in different situations were carried out: in normal physiological conditions, with hypertension and in more severe conditions caused by a trauma or an accident

Influencia de la edad y los aneurismas en la rotura de la pared aorta ascendente

Para mejorar los criterios de diagnóstico y prevención de las enfermedades cardiovasculares resulta fundamental conocer las propiedades mecánicas de la pared arterial. Este trabajo estudia el comportamiento mecánico y la rotura de la aorta torácica ascendente humana, tanto para individuos sanos como en pacientes aneurismáticos. Se estudia, asimismo, la influencia de la edad en las propiedades mecánicas. Se ha evaluado el comportamiento mecánico hasta rotura de la aorta torácica ascendente de 23 donantes sanos cuyas edades varían desde los 15 a los 65 años, y de 14 pacientes aneurismáticos, con edades entre 40 y 87 años. Se han realizado ensayos de tracción tanto en dirección longitudinal como circunferencial para evaluar la anisotropía de la pared arterial. Los resultados muestran que la influencia de la edad en las propiedades mecánicas de la pared arterial es significativa, tanto para los individuos sanos como para los enfermos. No se encuentran diferencias significativas entre el comportamiento en rotura de las sanas y las aneurismáticas cuando se comparan pacientes de las mismas edades. En cambio, la zona de trabajo fisiológico de las aortas enfermas se sitúa en la parte más rígida de su respuesta mecánica, perdiendo parte de su función amortiguadora de las ondas de presión generadas por el corazón

Análisis mecánico de un bypass coronario término-terminal

La técnica del bypass coronario consiste en evitar una arteria coronaria obstruida utilizando un injerto vascular. Su éxito depende del buen funcionamiento de la zona de unión, o anastomosis, entre la aorta y el injerto, y entre el injerto y la arteria coronaria. Las tensiones generadas en la discontinuidad pueden producir problemas de desgarro o roturas. El objetivo de este trabajo es analizar la unión mecánica que se produce al sustituir una arteria coronaria por otro vaso, estudiando las tensiones desarrolladas en la zona de anastomosis y su efecto sobre la integridad del conjunto. Se ha caracterizado el comportamiento mecánico de los vasos involucrados y se ha preparado un modelo numérico que reproduce el funcionamiento de un bypass término-terminal. Los resultados muestran que el diámetro, el espesor y la rigidez o flexibilidad del injerto en comparación con la arteria coronaria sustituida son parámetros de gran importancia

Mechanical characterization of the human thoracic descending aorta Experiments and modelling

This work presents experiments and modelling aimed at characterising the passive mechanical behaviour of the human thoracic descending aorta. To this end, uniaxial tension and pressurisation tests on healthy samples corresponding to newborn, young and adult arteries are performed. Then, the tensile measurements are used to calibrate the material parameters of the Holzapfel constitutive model. This model is found to adequately adjust the material behaviour in a wide deformation range; in particular, it captures the progressive stiffness increase and the anisotropy due to the stretching of the collagen fibres. Finally, the assessment of these material parameters in the modelling of the pressurisation test is addressed. The implication of this study is the possibility to predict the mechanical response of the human thoracic descending aorta under generalised loading states like those that can occur in physiological conditions and/or in medical device application

Caracterización mecánica de los vasos utilizados en un Bypass Coronario.

La técnica del bypass coronario consiste en evitar una arteria coronaria obstruida utilizando un injerto vascular. Su éxito depende del buen funcionamiento de la zona de unión, o anastomosis, entre la aorta y el injerto, y entre el injerto y la arteria coronaria. Las tensiones generadas en la discontinuidad pueden producir problemas de desgarro o roturas. El objetivo de este trabajo es analizar la unión mecánica que se produce al sustituir una arteria coronaria por otro vaso, caracterizando el comportamiento mecánico de los vasos involucrados

Impact of COVID-19 on cardiovascular testing in the United States versus the rest of the world

Objectives: This study sought to quantify and compare the decline in volumes of cardiovascular procedures between the United States and non-US institutions during the early phase of the coronavirus disease-2019 (COVID-19) pandemic. Background: The COVID-19 pandemic has disrupted the care of many non-COVID-19 illnesses. Reductions in diagnostic cardiovascular testing around the world have led to concerns over the implications of reduced testing for cardiovascular disease (CVD) morbidity and mortality. Methods: Data were submitted to the INCAPS-COVID (International Atomic Energy Agency Non-Invasive Cardiology Protocols Study of COVID-19), a multinational registry comprising 909 institutions in 108 countries (including 155 facilities in 40 U.S. states), assessing the impact of the COVID-19 pandemic on volumes of diagnostic cardiovascular procedures. Data were obtained for April 2020 and compared with volumes of baseline procedures from March 2019. We compared laboratory characteristics, practices, and procedure volumes between U.S. and non-U.S. facilities and between U.S. geographic regions and identified factors associated with volume reduction in the United States. Results: Reductions in the volumes of procedures in the United States were similar to those in non-U.S. facilities (68% vs. 63%, respectively; p = 0.237), although U.S. facilities reported greater reductions in invasive coronary angiography (69% vs. 53%, respectively; p < 0.001). Significantly more U.S. facilities reported increased use of telehealth and patient screening measures than non-U.S. facilities, such as temperature checks, symptom screenings, and COVID-19 testing. Reductions in volumes of procedures differed between U.S. regions, with larger declines observed in the Northeast (76%) and Midwest (74%) than in the South (62%) and West (44%). Prevalence of COVID-19, staff redeployments, outpatient centers, and urban centers were associated with greater reductions in volume in U.S. facilities in a multivariable analysis. Conclusions: We observed marked reductions in U.S. cardiovascular testing in the early phase of the pandemic and significant variability between U.S. regions. The association between reductions of volumes and COVID-19 prevalence in the United States highlighted the need for proactive efforts to maintain access to cardiovascular testing in areas most affected by outbreaks of COVID-19 infection

Combined searches for the production of supersymmetric top quark partners in proton-proton collisions at root s=13 TeV

A combination of searches for top squark pair production using proton-proton collision data at a center-of-mass energy of 13 TeV at the CERN LHC, corresponding to an integrated luminosity of 137 fb(-1) collected by the CMS experiment, is presented. Signatures with at least 2 jets and large missing transverse momentum are categorized into events with 0, 1, or 2 leptons. New results for regions of parameter space where the kinematical properties of top squark pair production and top quark pair production are very similar are presented. Depending on themodel, the combined result excludes a top squarkmass up to 1325 GeV for amassless neutralino, and a neutralinomass up to 700 GeV for a top squarkmass of 1150 GeV. Top squarks with masses from 145 to 295 GeV, for neutralino masses from 0 to 100 GeV, with a mass difference between the top squark and the neutralino in a window of 30 GeV around the mass of the top quark, are excluded for the first time with CMS data. The results of theses searches are also interpreted in an alternative signal model of dark matter production via a spin-0 mediator in association with a top quark pair. Upper limits are set on the cross section for mediator particle masses of up to 420 GeV

Search for new particles in events with energetic jets and large missing transverse momentum in proton-proton collisions at root s=13 TeV

A search is presented for new particles produced at the LHC in proton-proton collisions at root s = 13 TeV, using events with energetic jets and large missing transverse momentum. The analysis is based on a data sample corresponding to an integrated luminosity of 101 fb(-1), collected in 2017-2018 with the CMS detector. Machine learning techniques are used to define separate categories for events with narrow jets from initial-state radiation and events with large-radius jets consistent with a hadronic decay of a W or Z boson. A statistical combination is made with an earlier search based on a data sample of 36 fb(-1), collected in 2016. No significant excess of events is observed with respect to the standard model background expectation determined from control samples in data. The results are interpreted in terms of limits on the branching fraction of an invisible decay of the Higgs boson, as well as constraints on simplified models of dark matter, on first-generation scalar leptoquarks decaying to quarks and neutrinos, and on models with large extra dimensions. Several of the new limits, specifically for spin-1 dark matter mediators, pseudoscalar mediators, colored mediators, and leptoquarks, are the most restrictive to date.Peer reviewe

Measurements of Higgs boson production cross sections and couplings in the diphoton decay channel at root s=13 TeV

Measurements of Higgs boson production cross sections and couplings in events where the Higgs boson decays into a pair of photons are reported. Events are selected from a sample of proton-proton collisions at root s = 13TeV collected by the CMS detector at the LHC from 2016 to 2018, corresponding to an integrated luminosity of 137 fb(-1). Analysis categories enriched in Higgs boson events produced via gluon fusion, vector boson fusion, vector boson associated production, and production associated with top quarks are constructed. The total Higgs boson signal strength, relative to the standard model (SM) prediction, is measured to be 1.12 +/- 0.09. Other properties of the Higgs boson are measured, including SM signal strength modifiers, production cross sections, and its couplings to other particles. These include the most precise measurements of gluon fusion and vector boson fusion Higgs boson production in several different kinematic regions, the first measurement of Higgs boson production in association with a top quark pair in five regions of the Higgs boson transverse momentum, and an upper limit on the rate of Higgs boson production in association with a single top quark. All results are found to be in agreement with the SM expectations.Peer reviewe

Measurements of the Electroweak Diboson Production Cross Sections in Proton-Proton Collisions at root s=5.02 TeV Using Leptonic Decays

The first measurements of diboson production cross sections in proton-proton interactions at a center-of-mass energy of 5.02 TeV are reported. They are based on data collected with the CMS detector at the LHC, corresponding to an integrated luminosity of 302 pb(-1). Events with two, three, or four charged light leptons (electrons or muons) in the final state are analyzed. The WW, WZ, and ZZ total cross sections are measured as sigma(WW) = 37:0(-5.2)(+5.5) (stat)(-2.6)(+2.7) (syst) pb, sigma(WZ) = 6.4(-2.1)(+2.5) (stat)(-0.3)(+0.5)(syst) pb, and sigma(ZZ) = 5.3(-2.1)(+2.5)(stat)(-0.4)(+0.5) (syst) pb. All measurements are in good agreement with theoretical calculations at combined next-to-next-to-leading order quantum chromodynamics and next-to-leading order electroweak accuracy