It is widely known that Central Corneal Thickness (CCT) and Radius of Curvature (RoC) in uence the estimated IntraOcular Pressure (IOP) obtained from Goldmann Applanation Tonometry (GAT). However, not much is known about the in uence of corneal material properties, especially in a clinical setting. Several numerical studies have been conducted in an attempt to quantify the in uence of corneal material properties on the IOP. These studies agree that corneal material properties do in uence the estimated IOP, which contradict the initial premise on which GAT was designed, namely that material properties do not in uence the obtained GAT readings. Also, there is no consensus among these studies with respect to corneal material properties, thus a wide range of proposed properties exist. A possible explanation for this range of available corneal properties is the numerical modi elling assumptions used, which seem to be quite different. Different sets of experimental in ation test data were used to calibrate the constitutive models and different limbal boundary conditions were applied to simulate the experimental setup as well as in vivo conditions during GAT simulations. Therefore the purpose of this study is to determine whether these modelling assumptions in uence the obtained IOP and ultimately the overall conclusions. A Finite Element (FE) model of the human cornea is developed, implementing a constitutive model to represent the complex corneal structure and two limbal boundary conditions. This model is then calibrated using two different sets of experimental in ation test data. During calibration of the fibre reinforced elastic constitutive model it is found that independent of the assumptions made regarding the material coe cients, that the numerical in ation data compare well with the experimental data for all cases. Using this model a GAT simulation is conducted to estimate the IOP and the in uence of the modelling assumptions, cornea geometry and material properties are then investigated. The results indicate that the modelling assumptions, cornea geometry and material properties do infuence the estimated IOP. However, when assuming the cornea ground substance stiffness to be constant, it is found that the in uence on IOP due to material properties is not as significant. A correction equation is also proposed to account for the corneal geometric properties by calibrating the numerical model for a numerically normal cornea. This is done by utilising the various data sets which are obtained during the calibration of the constitutive model with the experimental inflation test data. It is concluded that using only inflation data to calibrate the constitutive model is not sufficient to uniquely describe the corneal material. This is evident as different material data sets are obtained, even though the experimental inflation data is matched well for a variety of considered cases. Each of these material data sets, in conjunction with geometric properties, yield different estimates for IOP during GAT simulations. This study therefore recommends the use of additional experimental data, such as strip extensometry, along with inflation test data to adequately calibrate a numerical model. It should also be noted that when modelling GAT care should be taken when considering the choice of limbal boundary condition, experimental data for calibration and assumptions made with regards to material coe cients, as these choices could potentially influence the outcomes and conclusions of a study. / Dissertation (MEng)--University of Pretoria, 2014. / gm2014 / Mechanical and Aeronautical Engineering / unrestricted

Introduction: Diabetes is characterized by insufficient production of insulin and/or incapacity of this hormone in playing its functions. Such disease impairs the function of the endothelium, the latter capable of regulating the vascular tone and important in the control of inflammatory response as well. Once dysfunctional, the endothelium no longer exhibits such functions, occurring mostly redox imbalance, this one evident in diabetic patients. Nowadays, several studies point to endothelial dysfunction as a contributor in the development of diabetic vascular complications, while the practice of physical activity, although of low intensity, brings benefits in the handling of type 2 diabetes, including reduction of cardiovascular risk factors. Physical intervention as a therapeutic proposal appears to be a promising way in the clinical management of diabetes mellitus, probably avoiding the progression of systemic complications. Aim: To assess the vascular function and the REDOX balance in patients with type 2 diabetes mellitus (T2DM) before and after the cardiovascular rehabilitation for six weeks. Methods: 43 diabetic female patients aged 57.50 ± 2.02 years were selected from the ambulatory of Endocrinology at Prof. Alberto Antunes Teaching Hospital (Federal University of Alagoas). The diagnosis for T2DM was established according to the criteria of the Brazilian Society of Diabetes (2007). Initial assessment was performed by laboratory and clinical evaluation. The cardiovascular rehabilitation program consisted of six weeks of aerobic training (50 to 70% of the maximum heart rate), associated to endurance training. Four patients have completed the six weeks rehabilitation program. Assessment of biochemical profile (fasting and postprandial glucose, glicosilated hemoglobin, total cholesterol, VLDL, LDL, HDL, triglycerides, uric acid, albumin and creatinin), REDOX balance (SOD and catalase activity and lipid peroxidation) and quality of life (through the application of the SF-36) were performed before and after the rehabilitation program period. Indirect assessment of vascular function was performed by the Augmentation Index (AI), wave reflection, systolic and diastolic blood pressure and pulse pressure, which were obtained by the left radial artery tonometry (HEM-9000 AI device). Physical capacity was assessed by the six-minute walk test. Results: After rehabilitation, there was a significant reduction in the serum albumin levels (3.52 ± 0.478 vs 3.85 ± 0.50 mg/dL, P=0.0159) and an increase in the serum acid uric levels (5.00 ± 0.25 vs 4.57 ± 0.21 mg/dL, P=0.0298), without, however, alterations in the creatinin levels (P=0.3760). It was observed a reduction in the systolic and diastolic blood pressure (141.50 ± 3.67 vs 117.00 ± 6.01 mmHg, p<0.01; 77.75 ± 1.48 vs 71.25 ± 3.03 mmHg, P<0.05, respectively) and in the pulse pressure (63.75 ± 2.29 vs 45.750 ± 3.68 mmHg, P<0.01), without improvement in the Augmentation Index, with an improvement in five parameters during the assessment of the quality of life: physical functioning (25.00 ± 17.56 vs 93.75 ± 6.25 %, P<0.05), vitality (31.250 ± 10.48 vs 87.50 ± 5.20 %, P<0.05), social functioning (50.00 ± 17.68 vs 100.00 ± 0.00 %, P<0.05), role physical (47.50 ± 8.53 vs 92.50 ± 3.22 %, P<0.01) and bodily pain (21.62 ± 10.68 vs 65.75± 12.49 %, P<0.01). There were no statistically significant changes neither in the glycemic and lipid profiles nor in the functional capacity. Conclusion: The cardiovascular rehabilitation program during six weeks in diabetic patients was capable of promoting improvement in hemodynamic parametres and in the quality of life, without greater changes in the biochemical profile and functional capacity. These observations permit to consider that in diabetic patients the cardiovascular rehabilitation should be initiated as soon as possible to promote a reduction in the cardiovascular risk in these individuals. / Introdução: O diabetes caracteriza-se pela produção insuficiente de insulina e/ou pela incapacidade desse hormônio em desempenhar suas funções. Tal doença prejudica a função do endotélio, tecido este capaz de regular o tônus vascular e a resposta inflamatória. Quando disfuncional, esta camada celular não mais exibe tais funções, ocorrendo, principalmente, o desbalanço redox, evidente em pacientes diabéticos. Atualmente, diversos estudos apontam para a disfunção endotelial como contribuinte para o desenvolvimento das complicações vasculares diabéticas, ao passo que a prática de atividade física, ainda que de baixa intensidade, traz benefícios no manejo do diabetes mellitus tipo 2, incluindo redução dos fatores de risco cardiovascular. Desta forma, a intervenção física como proposta terapêutica apresenta-se promissora no manejo clinico do diabetes mellitus, podendo evitar a progressão de complicações sistêmicas. Objetivo: Avaliar a função vascular e o balanço redox em pacientes portadores de diabetes mellitus tipo 2 (DMII), antes e após a reabilitação cardiovascular por seis semanas. Método: 43 pacientes do sexo feminino com idade média de 57,50 ± 2,02 foram selecionadas do ambulatório de Endocrinologia do Hospital Universitário Prof. Alberto Antunes (Universidade Federal de Alagoas). O diagnóstico de DMII foi estabelecido de acordo com os critérios da Sociedade Brasileira de Diabetes (2007). A avaliação inicial foi feita através de exames clínicos e laboratoriais. O programa de reabilitação cardiovascular consistiu de seis semanas de exercício aeróbio (50 a 70% da freqüência cardíaca máxima) associado a exercícios resistidos. Quatro pacientes completaram as seis semanas de reabilitação. Avaliação do perfil bioquímico (glicemia de jejum e pós-prandial, hemoglobina glicosilada, colesterol total, VLDL, LDL, HDL, triglicerídeos, ácido úrico, albumina e creatinina), balanço REDOX (atividades da SOD e catalase e peroxidação lipídica) e qualidade de vida (através da aplicação do SF-36) foram realizadas antes e após o programa de reabilitação. A avaliação indireta da função vascular foi realizada através do Augmentation Index (AI), onda de reflexão, pressões arteriais sistólica e diastólica e pressão de pulso, obtidos por tonometria da artéria radial esquerda (com o equipamento HEM-9000 AI). A capacidade física foi avaliada através do teste de caminhada de seis minutos. Resultados: Após a reabilitação, houve redução significativa dos níveis séricos albumina (3,52 ± 0,478 vs 3,85 ± 0,50 mg/dL, P=0,0159) e aumento dos níveis de ácido úrico (5,00 ± 0,25 vs 4,57 ± 0,21 mg/dL, P=0,0298), sem, entretanto, alterações dos níveis de creatinina (p=0,3760). Também foram reduzidas as pressões arteriais sistêmicas sistólica e diastólica (141,50 ± 3,67 vs 117,00 ± 6,01 mmHg, P<0,01; 77,75 ± 1,48 vs 71,25 ± 3,03 mmHg, P<0,05, respectivamente) e a pressão de pulso (63,75 ± 2,29 vs 45,750 ± 3,68 mmHg, P<0,01), sem redução no Augmentation Index, com melhora em cinco parâmetros da qualidade de vida: aspectos físicos (25,00 ± 17,56 vs 93,75 ± 6,25 %, P<0,05), vitalidade (31,250 ± 10,48 vs 87,50 ± 5,20 %, P<0,05), aspectos sociais (50,00 ± 17,68 vs 100,00 ± 0,00 %, P<0,05), capacidade funcional (47,50 ± 8,53 vs 92,50 ± 3,22 %, P<0,01) e dor (21,62 ± 10,68 vs 65,75 ± 12,49 %, P<0,01). Não foram observadas variações estatisticamente significativas para o perfil glicêmico, lipídico e capacidade funcional. Conclusão: O programa de reabilitação cardiovascular por seis semanas em pacientes diabéticas foi capaz de promover melhora em parâmetros hemodinâmicos e na qualidade de vida, sem maiores mudanças no perfil bioquímico e capacidade funcional. Estas observações permitem considerar que em pacientes diabéticos a reabilitação cardiovascular deve ser iniciada o mais precoce possível a fim de promover redução do risco cardiovascular nestes indivíduos.