Title: The effect of menstrual cycle phases on muscle tone Goals and methods: The aim of this thesis is to prove the effect of menstrual cycle phases and participating hormons on the viscoelastic properties of the sceletal calf muscle via the non-invasive myotonometer device. The experimental part of this thesis is a pilot study in which participated seven female probands aged inbetween 24 to 28. Each proband participated in four weekly tests. Only probands who had not used hormonal contraception for at least six months were selected. Results: The results of the tests are represented in graphs picturing parts of curves representing the force caused by the tip of the myotonometer. The muscle soleus tension is changing throughout the menstrual cycle but its impossible to eliminate other endogenous and exogenous factors. The measured relative values of muscle tension are different for each proband. The menstrual phase has the highest average value of muscle tension. It is not possible to make a generally valid conclusion. Key words: Menstrual cycle, menstrual phase, muscle tone, calf muscle, biomechanical properties, myotonometry, contraception

Le collagène de type I représente la protéine structurale la plus abondante au sein de l'organisme. Au cours du vieillissement, cette protéine à longue demi-vie biologique subit des modifications structurales et fonctionnelles qui affectent les propriétés biomécaniques des tissus. L'un des mécanismes majeurs est la réaction de glycation non enzymatique qui conduit à la formation des produits de glycation avancée (AGEs). Les AGEs entraînent une augmentation de la rigidité du collagène I qui se traduit par une désorganisation des réseaux fibrillaires et une perte d'élasticité tissulaire au cours du vieillissement. Dans cette étude, nous avons développé diverses approches biophotoniques afin d'étudier l'impact du vieillissement sur le collagène de type I, de façon rapide, directe et non destructive. Par microspectroscopies vibrationnelles infrarouge (IR) et Raman, des marqueurs spectroscopiques liés à l'accumulation des AGEs ont été mis en évidence au niveau des lyophilisats de collagènes de type I glyqués in vitro. Ces marqueurs sont retrouvés au niveau des lyophilisats de collagènes de type I d'âges différents et permettent une bonne discrimination des échantillons en fonction de l'âge. La bande spécifique des glucides apparaît ainsi comme un bon marqueur spectroscopique de la glycation, corrélant avec le taux d'AGEs fluorescents. Les pics spécifiques des résidus de proline permettent également de mettre en évidence les changements conformationnels dans la protéine dus à l'augmentation des liaisons croisées. L'imagerie IR appliquée aux tissus murins d'âges différents permet de retrouver ces différences spectrales in situ en fonction de l'âge. L'impact du vieillissement sur le comportement structural des fibrilles de collagène I a été étudié par microscopie multiphoton de second harmonique résolue en polarisation (PSHG). A l'échelle de la fibrille isolée, le vieillissement entraîne une perte de la complexité d'assemblage des fibrilles et une diminution de leur diamètre. L'effet de l'âge sur les propriétés biomécaniques du collagène de type I a été évalué sur des modèles de matrices 3D de collagène de type I, en présence de fibroblastes, par une technique de déformation des matrices et par tomographie à cohérence optique (OCT). Les résultats montrent une diminution du module d'élasticité et de la contraction du collagène avec le vieillissement, en accord avec les données de l'étude cinétique de la fibrillogenèse. Cette étude démontre la complémentarité des techniques biophotoniques employées et leur potentiel dans la caractérisation moléculaire et morphologique des effets de l'âge sur le collagène de type I, de manière directe, non invasive et multi-échelles. / Type I collagen represents the most abundant structural protein in the human body. During aging, this long half-life protein undergoes structural and functional changes which affect the biomechanical properties of tissues. One of the main mechanisms is the non enzymatic glycation leading to the formation of the so-called advanced glycation endprodutcs (AGEs). AGEs give rise to an increase of collagen I rigidity which is responsible for the fibrillar network disorganization and the loss of tissue elasticity with age. In this work, we applied various biophotonic approaches for studying the impact of aging on type I collagen, in a rapid, direct and non destructive way. Using vibrational infrared (IR) and Raman microspectroscopies, we highlighted spectroscopic markers linked to AGEs accumulation in freeze-dried samples of in vitro-glycated type I collagens. These markers were also detected in different-age freeze-dried type I collagens and allowed a clear discrimination of samples as a function of age. The band assigned to carbohydrates appears like a specific spectroscopic marker of glycation, in correlation with the fluorescent-AGEs quantification. The specific peaks for proline residues allow highlighting conformational changes in protein backbone due to a higher cross-linking. IR imaging applied to tissues from different-age rats can detect these spectral differences in situ as a function of age. Impact of aging on the structural behaviour of type I collagen fibrils was studied by polarization resolved second harmonic generation (PSHG) multiphoton microscopy. At the scale of single fibril, aging gives rise to a loss of fibril assembly complexity and a decrease of fibril diameter. Age effect on biomechanical properties of type I collagen was evaluated on 3D type I collagen matrice models in the presence of fibroblasts, using an indentation technique and optical coherence tomography (OCT). Results show a decrease of both elastic modulus and collagen contraction with aging, in agreement with kinetics of the fibrillogenesis process. This study demonstrates the complementarity of the different biophotonic techniques used in our multimodal approach and their potential for characterizing age effects on type I collagen, in a direct, non invasive and multi-scale way.

Made available in DSpace on 2016-06-02T20:19:12Z (GMT). No. of bitstreams: 1 2618.pdf: 1011844 bytes, checksum: acc696873b3edd56b2bb4801a43ed7e8 (MD5) Previous issue date: 2009-08-07 / Financiadora de Estudos e Projetos / Osteoporosis is generally a systematic skeletal disease characterized by low bone density and microarchitectural deterioration of bone tissue with a consequent increase in bone fragility. Osteopenia is characterised by a lower bone density than normal bone tissue but higher than osteoporotic bone tissue. Osteoporosis and osteopenia represent a severe health threat to elderly people and they have recently been recognised as a major public health problem. They are related with some clinic manifestations, mainly the increase of the fractures risk. In this context, there is a critical need to develop technologies able of treating osteoporotic and osteopenic fractures. Promising treatments are the use of biomaterials and the Low Level Laser Therapy (LLLT), which seem to induce osteogenesis and stimulate fracture healing. The aim of this study was to determine the effects of the Biosilicate® and the LLLT on bone consolidation of osteopenic rat. Seventy female Wistar rats (12 weeks-old, ± 250g) ovariectomy (OVX) was carried on. The animals were randomly divided into 7 groups, with 10 animals each: standard control (CP); defect bone control (CD), bone defect treated with Biosilicate® (B), bone defect treated with laser 60J/cm2 (L60), bone defect treated with laser 120J/cm2 (L120), bone defect treated with both treatments Biosilicate® and laser 60J/cm2 (B+L60), bone defect treated with both treatments Biosilicate® and laser 120J/cm2 (B+L120). Sixty days post-OVX the osteotomies were surgically performed on the left tibia. In the Biosilicate® treated animals, the cavities were carefully filled with the biomaterial. An 830nm laser was performed for seven sessions. On day 14 post-osteotomy, rats were sacrificed and the tibias were defleshed. Biomechanical properties of the tibia were determined by two tests: the Indentation Test to a depth of 0-0.5mm, 0-1.0mm and 0-1.5mm and the Three-Point Bending Test. From de load-deformation curve, the maximal load (KN) and energy absorption (J) were obtained. Statistical analyses were performed using Kruskal-Wallis Test and Mann-Whitney U Test, with the level of significance of 5% (p&#8804;0.05). In relation to biomechanical properties of the Indentation Test, the groups CP, B, B+L60 and B+L120 presented higher statistically values (p<0.05) in relation to group CD. The better biomechanical answer among the groups was present by the group with Biosilicate® utilization in association of 120J/cm². In relation to maximal load of the Three-Point Bending Test, the group L60 presented higher statistically values (p< 0.05) in relation to group CP, B, L120, B+L60, B+L120 and the groups had similar values of absorption energy. The Biosilicate® application raised the biomechanical properties of the callus bone, but didn t raise the biomechanical properties of the tibia determined by Three-Point Bending Test. In the two biomechanical tests, the groups with treatment based only on laser irradiation haven t presented significant results in relation to group control fracture. The bones defects treated with both treatments Biosilicate® and laser 120J/cm2 presented higher biomechanical properties of the callus bone in relation to the group based only Biosilicate® application. / A osteoporose é uma doença esquelética sistêmica caracterizada por baixa densidade óssea e deterioração da microarquitetura do tecido ósseo com conseqüente aumento da fragilidade óssea. A osteopenia é caracterizada por apresentar uma menor densidade óssea que o tecido ósseo normal, mas maiores valores do que o tecido ósseo osteoporótico. A osteoporose e a osteopenia representam um grave problema de saúde a idosos e recentemente têm sido reconhecidos como um dos principais problemas de saúde pública, principalmente por aumentar o risco de fraturas. Neste contexto, há uma grande necessidade de se desenvolver tecnologias capazes de tratar fraturas em organismos osteoporóticos e osteopênicos. Existem diversos tratamentos promissores, como o uso do Biosilicato® e da terapia laser, os quais parecem induzir a osteogênese e estimulam o reparo ósseo. O objetivo deste estudo foi determinar os efeitos do o Biosilicato® e da terapia laser sobre o reparo ósseo de ratas osteopênicas. Setenta ratas fêmeas da raça Wistar (12-semanas, ± 250g) foram ovariectomizadas e divididas em sete grupos com 10 animais em cada: controle padrão (CP), controle com defeito ósseo (CD), tratado com Biosilicato® (B), tratado com 60J/cm2 (L60), tratado com 120J/cm2 (L120), tratado com Biosilicato® e 60J/cm2 (B+L60), tratado com Biosilicato® e 120J/cm2 (B+L120). Sessenta dias após a ovariectomia, as tíbias foram osteotomizadas. Nos animais tratados com Biosilicato®, a cavidade do defeito ósseo foi preenchida com o biomaterial. Os animais foram irradiados com 830nm por sete sessões (48- 48h). No décimo quarto dia após a osteotomia, as ratas foram sacrificadas e as tíbias dessecadas. As propriedades biomecânicas das tíbias esquerdas foram determinadas por dois testes: O Teste de Endentação com profundidade de 0-0,5mm, 0-1,0mm e 0-1,5mm que avaliou as propriedades biomecânicas do calo ósseo e o Teste de Flexão a Três Pontos que avaliou as propriedades biomecânicas das regiões ósseas integras do osso osteotomizado, sem considerar a região do calo ósseo que foi utilizada no teste de Endentação. A carga máxima (KN) e a energia de absorção (J) foram obtidas da curva de carga-deslocamento. A análise estatística foi realizada pelo Teste de Kruskal-Wallis e o Teste de Mann-Whitney U, com p&#8804;0,05. Em relação ao Teste de Endentação, os grupos CP, B, B+L60 e B+L120 apresentaram maiores valores estatísticos (p<0,05) em relação ao grupo CD. A melhor resposta biomecânica do Teste de Endentação foi apresentada pelo grupo B+L120. Em relação à carga máxima do Teste de Flexão a Três Pontos, o grupo L60 apresentou maiores valores estatísticos (p<0,05) do que os grupos CP, B, L120, B+L60, B+L120 e todos os grupos tiveram valores semelhantes de energia de absorção. Pode-se concluir que a aplicação do Biosilicato® aumentou as propriedades biomecânicas do calo ósseo e não alterou as propriedades das regiões ósseas integras. A terapia laser não promoveu diferença significativa das propriedades biomecânicas do calo ósseo e das regiões ósseas integras e a associação dos dois tratamentos com fluência de 120J/cm² promoveu um aumento das propriedades biomecânicas do calo ósseo a valores mais elevados do que o grupo que utilizou somente o biomaterial.

Made available in DSpace on 2016-06-02T19:22:10Z (GMT). No. of bitstreams: 1 5474.pdf: 2975915 bytes, checksum: e9d30ed81c2e8431af179d83ebf62b96 (MD5) Previous issue date: 2013-05-10 / Universidade Federal de Sao Carlos / Lead acetate (Pb) is a nonessential and highly toxic heavy metal which is released to the environment by several routes, mainly by industrial and mining activities. Recent studies have suggested that lead caused a decrease in femur strength of adult rats. A wide range of chelating has been evaluated as possible protective agents against lead acetate toxicity. Dissodium ethylenediaminetetraacetate (Na2EDTA) is the chelating agent most widely used in the treatment of Pb poisoning. The chelating therapy with EDTA might induce Pb mobilization from inert deposition organs toward such critical tissues as the brain. But, it is questioned the safety of the use of this compound in the management of Pb poisoning. The lack of safety and efficacy demonstrated by conventional chelating has encouraged the search for new ways to remove heavy metals from the body. Recently, a supplementation of Chlorella vulgaris extract (CV) was shown to alleviate the heavy metals toxicity in rats. The aim of this study was to evaluate possible protective influence of Chlorella and Na2EDTA supplementation on bone physical and biomechanical properties of rats exposed to lead acetate. For this purpose, male Wistar rats were distributed into eight groups (n=8): Control (0.9% saline 0.1 ml/100g body weight- BW), EDTA (150 mg/Kg BW), CV 50 (50 mg/Kg BW), CV 250 (250 mg/Kg BW), Pb (250 mg/Kg BW), Pb (250 mg/Kg BW) plus EDTA (150 mg/Kg BW), Pb (250 mg/Kg BW) plus CV 50 (50 mg/Kg BW) and Pb (250 mg/Kg BW) plus CV 250 (250 mg/Kg BW). The treatment was done once a week, for 8 weeks by gastric gavage. Bone volume, bone mineral density (BMD) and biomechanical properties (maximum load, resilience and stiffness) of the femoral diaphysis and 5th lumbar vertebra were examined. The biomechanical properties of femurs were obtained by the three-points bending test and compression test for vertebrae, using a universal test machine Instron, model 4444. Bone MMP-2 activitie was measured by gelatin zymography. Concentrations of lead and zinc in whole blood and lead, zinc, calcium and magnesium in the left femur and 4th lumbar vertebra were determined by ICP-MS (Inductively Coupled Plasma Mass Spectrometry). Exposure to 250 mg/kg BW of Pb caused significant reduction of maximum load, stiffness and resilience indicating the ability of this element to damage the quality of bone tissue. In the 5th lumbar vertebrae, exposure to Pb caused significant reduction of bone mineral density. The treatment with Chlorella vulgaris (50 mg/kg BW and 250 mg/Kg BW) and EDTA (150 mg/Kg BW) during Pb exposure prevented the weakening of the bone strength. In the 5th lumbar vertebrae, the CV and EDTA prevented the reduction of bone mineral density due to Pb. The pro, intermediate and active MMP-2 activity in bone of animals exposed to lead showed a significant increase compared to control. The CV 50 administration in animals exposed to lead reduced the activity of MMP-2 isoforms in their pro, intermediate and active levels compared to control group. The exposure to Pb resulted in an increase of the blood concentration of this heavy metal and its accumulation in the liver, kidney, brain and bone concentration. The CV and EDTA reduced blood lead concentrations, leading to reduction of lead concentration in liver, kidney, brain and bone. These findings seem to indicate that treatment with Chlorella vulgaris and EDTA during exposure to Pb may be beneficial for the skeleton of subjects chronically exposed to Pb. / O chumbo, um metal não-essencial e altamente tóxico, é liberado no ambiente por diversas vias, principalmente através da atividade industrial e mineração. Estudos recentes sugerem que o acetato de chumbo causa redução da resistência óssea em ratos. Uma grande variedade de quelantes tem sido usada como possíveis agentes protetores contra a toxicidade provocada pelo acetato de chumbo. Etilenodiaminotetraacetato Cálcico Dissódico (EDTA) é o agente quelante mais usado no tratamento do envenenamento por chumbo. A terapia quelante com EDTA pode induzir redistribuição do chumbo endógeno e sua deposição em órgãos críticos, tal como o cérebro. Entretanto, é questionada a segurança do uso deste composto no tratamento do envenamento com chumbo. A falta de segurança e eficácia demonstrada pelos quelantes convencionais tem encorajado pesquisas por novas maneiras de remover metais tóxicos do organismo. Recentemente, uma suplementação com Extrato de Chlorella vulgaris (CV) mostrou aliviar a toxicidade de metais tóxicos em ratos. O objetivo deste estudo foi avaliar a possível influência protetora da suplementação com Chlorella e Na2EDTA sobre as propriedades físicas e biomecânicas ósseas de ratos expostos ao acetato de chumbo. Para este propósito, ratos Wistar foram distribuídos em oito grupos (=8): Controle (0,9% salina 0,1 ml/100g massa corporal - MC), EDTA (150 mg/Kg MC), CV 50 (50 mg/Kg MC), CV 250 (250 mg/Kg MC), Pb (250 mg/Kg MC), Pb (250 mg/Kg MC) mais EDTA (150 mg/Kg MC), Pb (250 mg/Kg MC) mais CV 50 (50 mg/Kg MC) e Pb (250 mg/Kg MC) mais CV 250 (250 mg/Kg MC). O tratamento foi realizado uma vez por semana, durante 8 semanas por gavagem gástrica. Volume ósseo, densidade mineral óssea (DMO) e densidade óssea (DO) e propriedades biomecânicas (força máxima, rigidez e resiliência) da diáfise femoral e das quintas vértebras lombares foram examinados. As propriedades biomecânicas dos fêmures foram obtidas pelo teste de flexão a três pontos e das vértebras pelo teste de compressão, usando uma máquina universal Instron 4444. A atividade de MMP-2 óssea foi mensurada por zimografia de gelatina. Foram também realizadas as análises das concentrações de Pb e Zn no sangue, fígado, rim, cérebro e ossos e das concentrações de Ca e Mg nos fêmures e vértebras determinadas por Espectometria de Emissão Atômica. A exposição ao Pb, na dose de 250 mg/Kg MC causou redução significativa da força máxima, rigidez e resiliência dos fêmures, indicando a habilidade deste elemento em prejudicar a qualidade do tecido ósseo. Nas vértebras, a exposição ao chumbo causou redução da densidade mineral óssea. O tratamento com Chlorella vulgaris (50 mg/kg MC e 250 mg/Kg MC) ou EDTA (150 mg/Kg MC) durante exposição ao chumbo, preveniu o enfraquecimento da resistência óssea dos fêmures. Na vértebra, o tratamento com Chlorella vulgaris (50 mg/kg MC e 250 mg/Kg MC) ou EDTA (150 mg/Kg MC) preveniu a redução da densidade mineral óssea. A atividade da MMP-2 pro, intermediária e ativa aumentaram nos ossos de animais expostos ao chumbo quando comparada ao controle. A administração de CV 50 aos animais expostos a este metal reduziu a atividade da MMP-2 nas suas isoformas pro, intermediária e ativa a níveis comparados ao controle. A exposição ao chumbo resulta em aumento da concentração de chumbo sanguínea e sua acumulação no fígado, rim, cérebro e ossos. O tratamento com CV ou EDTA reduziu as concentrações sanguíneas de chumbo, levando à redução da concentração de chumbo nos diversos órgãos estudados (fígado, rim, cérebro e ossos). Os resultados indicam que o tratamento com Chlorella vulgaris e EDTA durante a exposição ao chumbo pode ser benéfico ao osso de indivíduos expostos cronicamente ao acetato de chumbo.

On entend par substitut dermo-épidermique un épiderme reconstruit à la surface d'un derme équivalent composé de fibroblastes cultivés classiquement dans un biomatériau support, souvent à base de collagène poreux ou sous forme de gel. Ce support possède ses propres propriétés biomécaniques, influant sur la réponse biomécanique globale des peaux reconstruites, nous nous sommes donc intéressés à un modèle de peau reconstruite sans support, dans lequel le derme équivalent est « auto-assemblé » par les fibroblastes néosynthétisant leur propre matrice extracellulaire (MEC). Notre premier objectif a été d'optimiser et de caractériser ce modèle auto-assemblé en termes de structure, de reproductibilité et de fonctionnalité. Notre second objectif a été d'adapter aux peaux reconstruites in vitro (PR) des outils traditionnellement utilisés pour des études in vivo, pour explorer leurs propriétés biophysiques et biomécaniques. Ces outils permettent une exploration morphologique à des résolutions différentes avec l'échographie, la tomographie à cohérence optique (OCT) et la microscopie confocale à balayage et une exploration fonctionnelle des propriétés biomécaniques des PR par cutométrie. Ces données biophysiques ont ensuite été analysées par rapport aux résultats en histologie, immunohistologie et microscopie électronique à transmission. La cinétique de culture du modèle auto-assemblé sur un temps prolongé a montré la grande stabilité de l'épiderme et le remodelage continuel de la MEC avec notamment l'augmentation des fibres de collagène et d'élastine. Au temps de culture de référence sélectionné, correspondant à l'obtention de la différenciation terminale de l'épiderme, nous avons démontré la reproductibilité des épaisseurs de l'épiderme et du derme en histologie et en OCT, de la maturité de l'épiderme et de la jonction dermo-épidermique et de l'expression dermique de l'élastine colocalisée avec la fibrilline. Sur le plan fonctionnel, nous avons démontré la fonction barrière de l'épiderme via l'imperméabilité du stratum corneum et des jonctions serrées / A skin equivalent consist of a epidermis reconstructed on the top of a dermis equivalent classically composed of fibroblasts cultured into a biomaterial scaffold which is often a collagen gel or sponge. This scaffold hold its own mechanical properties, influencing the global skin equivalent biomechanical response, so we choose to develop a scaffold-free skin equivalent (SFSE), based on the ability of fibroblasts to synthezise their own extracellular matrix. Our first objective was to optimize and characterize the structure, the reproducibility and functionality of this scaffold-free model. Our second goal was to adapt biophysical and biomechanical tools classically used for in vivo evaluation to in vitro skin equivalents. Their morphology was explored with different resolutions using echography, optical coherence tomography (OCT) and laser scanning microscopy whereas biomechanical functionality was evaluate by a suction test, the cutometry. This biophysical data were compared to more classical histological, immununohistological and transmission electronic microscopy results. The long-term culture of the scaffold-free model showed the good stability of epidermis and the continuous remodelling of MEC with notably an increase of collagen and elastin fibers. We selected a reference culture time, corresponding to the complete terminal differentiation of epidermis. At this culture time, we showed the epidermis and dermis thickness reproducibity in histology and OCT, the constant epidermis and dermo-epidermal junction maturity and the dermal expression of elastin, colocalized with fibrillin. The barrier function of epidermis was also demonstrated via stratum corneum and tight junctions impermeability

Previous studies have shown favourable properties for papaya bast fibres, with a Young's modulus of up to 10 GPa and a tensile strength of up to 100 MPa. Because the fibres remain as residues on papaya plantations across the tropics in large quantities, their use in the making of green composites would seem to be worthy of consideration. This study aims to show that such composites can have very suitable mechanical properties, comparable to or even better than the common wood plastic composites (WPCs), and as such, represent a promising raw material for composites and a low-cost alternative to wood.

<p>   </p> <p>Mechanical loading models are used to study adaptive skeletal mechanobiology mechanisms. However, most studies have used mammal models, leaving a knowledge gap regarding how these mechanisms differ among vertebrate groups. To address this gap, we evaluated the <em>in vivo</em> bone strain environment of the left tibia in green iguanas during locomotion, axial compressive loading, and with finite element analysis (FEA). Our study involved examining subadult green iguanas (n=7) over a range of speeds (0.4 - 1.3 m/s) and axial load magnitudes (-25 to -100 N) to determine peak strains. Bone strains were measured using single-element strain gauges (n=18) and rosette strain gauges (n=3), surgically attached to the tibial anterior, posterior, and medial surfaces. At a speed of 1.3 m/s, peak strains ± standard deviation observed were 645 ± 699 µε, -448 ± 464 µε, and 206 ± 168 µε at the anterior, posterior, and medial surfaces, respectively. Peak principal tensile and compressive strains on the medial surface were 199 ± 113 µε and -153 ± 98 µε at 1.3 m/s. During -100 N compressive loading, peak strains were 403 ± 277 µε, -506 ± 460 µε, and -52 ± 177 µε at the anterior, posterior, and medial surfaces, respectively. Our FEA model demonstrated a close correlation with experimentally measured strain values at the gauge sites (slope = 1.07, R2=0.7). Using these foundational <em>in vivo</em> strain results and a daily strain stimulus formula, our objective was to develop a novel noninvasive axial compressive tibial loading model to induce a cortical bone adaptive response in the green iguana tibia. However, following three weeks of daily applied compressive loading, no significant difference was detected in critical bone parameters at 37% and 50% (midshaft) volumes of interests from the proximal tibia (P<0.05).  While this study did not yield significant differences in critical bone parameters following the application of daily compressive loading, it provided new knowledge regarding the bone strain environment and the potential for inducing adaptive responses in the green iguana tibia. Further research may refine our understanding of skeletal mechanobiology mechanisms across vertebrate groups and develop more effective loading models for studying bone adaptation. Overall, the findings of this study contribute to the broader field of musculoskeletal mechanobiology, giving insights that may inform bone health and adaptation in diverse species, including humans. </p> <p>  </p>

Justification: Le glaucome entraîne une perte progressive de la vision causée par la détérioration du nerf optique. Le glaucome est répandu dans le monde et cause la cécité dans environ sept millions de personnes. Le glaucome touche plus de 400 000 Canadiens et sa prévalence augmente avec le vieillissement de la population.1,2 Il s'agit d'une maladie chronique surnoise dont les symptômes se manifestent uniquement lors des stades avancés et qui peuvent mener à la cécité. Présentement, le seul moyen possible d’arrêter la progression du glaucome au stade initial est de diminuer la pression intra-oculaire (PIO). Les analogues de prostaglandines (APG) topiques sont fréquemment utilisées comme traitement de première ligne. Cependant, la recherche démontre que cette classe de médicaments peut changer certaines propriétés de la cornée, et possiblement influencer la mesure de la PIO.3 Objectif: À déterminer si l'utilisation d'APG affecte les propriétés biomécaniques de la cornée. La conclusion sera basée sur l'analyse intégrée des résultats obtenus de l'analyseur Reichert oculaire Réponse (ORA), la tonométrie par applanation de Goldmann (TAG) et la pachymétrie ultrasonographique. Le deuxième objectif potentiel de cette étude est de déterminer la corrélation, le cas échéant, entre les propriétés biomécaniques de la cornée, l'épaisseur de la cornée centrale (ECC) et la PIO chez les patients subissant un traitement d’APG topique. L'hypothèse principale de cette étude est que l’APG influence les propriétés de la cornée telles que l'épaisseur centrale, l'élasticité et la résistance. Patients et méthodes : Soixante-dix yeux de 35 patients, âgés de 50-85 ans, atteints de glaucome à angle ouvert (GAO) et traités avec APG topique ont été examinés. Seulement les sujets avec une réfraction manifeste entre -6,00 D et +4,25 D ont été inclus. Les critères d'exclusion sont: patients avec n'importe quelle autre maladie de la cornée de l’œil, telles que la dystrophie endothéliale de Fuch’s et kératocône, ou tout antécédent de traumatisme ou d'une chirurgie de la cornée, ainsi que le port de lentilles de contact. Nous avons demandé aux patients atteints du glaucome qui ont des paramètres stables et qui utilisent l’APG dans les deux yeux de cesser l’APG dans l'œil moins affecté par la PIO, et de continuer l’utilisation d’APG dans l'œil contralatéral. Le meilleur œil est défini comme celui avec moins de dommage sur le champ visuel (CV) (déviation moyenne (DM), le moins négatif) ou une PIO maximale historique plus basse si la DM est égale ou encore celui avec plus de dommage sur la tomographie par cohérence optique (TCO, Cirrus, CA) ou la tomographie confocale par balayage laser (HRT, Heidelberg, Allemagne). Toutes les mesures ont été prises avant la cessation d’APG et répétées 6 semaines après l’arrêt. Les patients ont ensuite recommencé l’utilisation d’APG et toutes les mesures ont été répétées encore une fois après une période supplémentaire de 6 semaines. Après commencer ou de changer le traitement du glaucome, le patient doit être vu environ 4-6 semaines plus tard pour évaluer l'efficacité de la goutte.4 Pour cette raison, on été décidé d'utiliser 6 semaines d'intervalle. Toutes les mesures ont été effectuées à l’institut du glaucome de Montréal par le même technicien, avec le même équipement et à la même heure de la journée. L'œil contralatéral a servi comme œil contrôle pour les analyses statistiques. La tonométrie par applanation de Goldmann a été utilisée pour mesurer la PIO, la pachymétrie ultrasonographique pour mesurer l'ECC, et l’ORA pour mesurer les propriétés biomécaniques de la cornée, incluant l'hystérèse cornéenne (HC). L’hypothèse de l'absence d'effet de l'arrêt de l’APG sur les propriétés biomécaniques a été examiné par un modèle linéaire à effets mixtes en utilisant le logiciel statistique R. Les effets aléatoires ont été définies à deux niveaux: le patient (niveau 1) et l'œil de chaque patient (niveau 2). Les effets aléatoires ont été ajoutés au modèle pour tenir compte de la variance intra-individuelle. L’âge a également été inclus dans le modèle comme variable. Les contrastes entre les yeux et les temps ont été estimés en utilisant les valeurs p ajustées pour contrôler les taux d'erreur internes de la famille en utilisant multcomp paquet dans R. Résultats: Une augmentation statistiquement significative due l 'HC a été trouvée entre les visites 1 (sur APG) et 2 (aucun APG) dans les yeux de l'étude, avec une moyenne (±erreur standard) des valeurs de 8,98 ± 0,29 mmHg et 10,35 ± 0,29 mmHg, respectivement, correspondant à une augmentation moyenne de 1,37 ± 0,18 mmHg (p <0,001). Une réduction significative de 1,25 ± 0,18 mmHg (p <0,001) a été observée entre les visites 2 et 3, avec une valeur moyenne HC finale de 9,09 ± 0,29 mmHg. En outre, une différence statistiquement significative entre l’oeil d’étude et le contrôle n'a été observée que lors de la visite 2 (1,01 ± 0,23 mmHg, p <0,001) et non lors des visites 1 et 3. Une augmentation statistiquement significative du facteur de résistance conréen (FRC) a été trouvée entre les visites 1 et 2 dans les yeux de l'étude, avec des valeurs moyennes de 10,23 ± 0,34 mmHg et 11,71 ± 0,34 mmHg, respectivement. Le FRC a ensuite été réduit de 1,90 ± 0,21 mmHg (p <0,001) entre les visites 2 et 3, avec une valeur moyenne FRC finale de 9,81 ± 0,34 mmHg. Une différence statistiquement significative entre l’oeil d’étude et le contrôle n'a été observée que lors de la visite 2 (1,46 ± 0,23 mmHg, p <0,001). Une augmentation statistiquement significative de l'ECC a été trouvée entre les visites 1 et 2 dans les yeux de l'étude, avec des valeurs moyennes de 541,83 ± 7,27 µm et 551,91 ± 7,27 µm, respectivement, ce qui correspond à une augmentation moyenne de 10,09 ± 0,94 µm (p <0,001). L'ECC a ensuite diminué de 9,40 ± 0,94 µm (p <0,001) entre les visites 2 et 3, avec une valeur moyenne finale de 542,51 ± 7,27 µm. Une différence entre l’étude et le contrôle des yeux n'a été enregistré que lors de la visite 2 (11,26 ± 1,79 µm, p <0,001). De même, on a observé une augmentation significative de la PIO entre les visites 1 et 2 dans les yeux de l'étude, avec des valeurs moyennes de 15,37 ± 0,54 mmHg et 18,37 ± 0,54 mmHg, respectivement, ce qui correspond à une augmentation moyenne de 3,0 ± 0,49 mmHg (p <0,001). Une réduction significative de 2,83 ± 0,49 mmHg (p <0,001) a été observée entre les visites 2 et 3, avec une valeur moyenne de la PIO finale de 15,54 ± 0,54 mmHg. L’oeil de contrôle et d’étude ne différaient que lors de la visite 2 (1,91 ± 0,49 mmHg, p <0,001), ce qui confirme l'efficacité du traitement de l’APG. Lors de la visite 1, le biais de la PIO (PIOcc - PIO Goldmann) était similaire dans les deux groupes avec des valeurs moyennes de 4,1 ± 0,54 mmHg dans les yeux de contrôles et de 4,8 ± 0,54 mmHg dans les yeux d’études. Lors de la visite 2, après un lavage de 6 semaines d’APG, le biais de la PIO dans l'œil testé a été réduit à 1,6 ± 0,54 mmHg (p <0,001), ce qui signifie que la sous-estimation de la PIO par TAG était significativement moins dans la visite 2 que de la visite 1. La différence en biais PIO moyenne entre l'étude et le contrôle des yeux lors de la visite 2, en revanche, n'a pas atteint la signification statistique (p = 0,124). On a observé une augmentation peu significative de 1,53 ± 0,60 mmHg (p = 0,055) entre les visites 2 et 3 dans les yeux de l'étude, avec une valeur de polarisation finale de la PIO moyenne de 3,10 ± 0,54 mmHg dans les yeux d'études et de 2,8 ± 0,54 mmHg dans les yeux de contrôles. Nous avons ensuite cherché à déterminer si une faible HC a été associée à un stade de glaucome plus avancé chez nos patients atteints du glaucome à angle ouvert traités avec l’APG. Lorsque l'on considère tous les yeux sur l’APG au moment de la première visite, aucune association n'a été trouvée entre les dommages sur le CV et l'HC. Cependant, si l'on considère seulement les yeux avec un glaucome plus avancé, une corrélation positive significative a été observée entre la DM et l'HC (B = 0,65, p = 0,003). Une HC inférieure a été associé à une valeur de DM de champ visuelle plus négative et donc plus de dommages liés au glaucome. Conclusions : Les prostaglandines topiques affectent les propriétés biomécaniques de la cornée. Ils réduisent l'hystérèse cornéenne, le facteur de résistance cornéen et l'épaisseur centrale de la cornée. On doit tenir compte de ces changements lors de l'évaluation des effets d’APG sur la PIO. Plus de recherche devrait être menées pour confirmer nos résultats. De plus, d’autres études pourraient être réalisées en utilisant des médicaments qui diminuent la PIO sans influencer les propriétés biomécaniques de la cornée ou à l'aide de tonomètre dynamique de Pascal ou similaire qui ne dépend pas des propriétés biomécaniques de la cornée. En ce qui concerne l'interaction entre les dommages de glaucome et l'hystérésis de la cornée, nous pouvons conclure qu' une HC inférieure a été associé à une valeur de DM de CV plus négative. Mots Clés glaucome - analogues de prostaglandines - hystérèse cornéenne – l’épaisseur de la cornée centrale - la pression intraoculaire - propriétés biomécaniques de la cornée. / Rationale: Glaucoma is a chronic disease that causes a gradual loss of vision due to progressive damage to the optic nerve. It is widespread in the world and causes blindness in about seven million people. In addition, it affects more than 400,000 Canadians and its prevalence is increasing with the aging of the population.1, 2 Glaucoma becomes symptomatic only in the more advanced stages of the disease, and currently, the goal of treatment is to halt the progression of the disease by lowering the intra-ocular pressure (IOP). Topical prostaglandin analogs (PGA) are currently the first line treatment, however research has shown that this class of medications may change certain properties of the cornea, and hence the measurement of IOP.3 Aim: To determine whether the use of topical prostaglandin analogs (PGA) affects the biomechanical properties of the cornea. The conclusion will be based on the integrated analysis of the data collected from the Reichert Ocular Response Analyzer (ORA), Goldmann tonometry and ultrasound pachymetry. The second potential aim of this study is to determine the correlations, if any, between the biomechanical properties of cornea, the Central Corneal Thickness (CCT) and IOP in patients undergoing topical PGA treatment. The main hypothesis of this study is that the PGA drops influence the properties of the cornea such as central thickness, elasticity and resistance. Patients and Methods: In this study, seventy eyes of 35 patients, aged 50 - 85 years, with open angle glaucoma (OAG) and treated with topical PGA were examined. Only subjects with a manifest refraction between -6.00 D and +4.25 D were included. Exclusion criteria included patients with any other corneal eye disease, such as Fuch’s endothelial dystrophy or keratoconus, or any past history of corneal trauma or surgery. Contact lens wearers were also excluded. Patients with stable glaucoma parameters who were using topical PGA in both eyes prior to the start of the study were asked to discontinue the PGA in the best eye and to continue the application of PGA to the contralateral eye. The "best" eye, representing the eye with the least amount of glaucoma-related damage, was selected based on the results of the Humphrey Visual Field (HFA, Carl Zeiss Meditec, Inc., Dublin, CA), Heidelberg Retinal Tomography (HRT II, Heidelberg Engineering GmbH, Heidelberg, Germany), Optical Coherence Tomography (CIRRUS HD-OCT, Carl Zeiss Meditec, Inc., Dublin, CA) and maximum IOP. The contralateral eye served as a control for statistical analyses. Corneal measurements were taken before PGA cessation and repeated 6 weeks after cessation. Patients then restarted the use of PGA and all measurements were repeated once more after an additional 6 weeks. After starting or changing glaucoma treatment the patient should be seen approximately 4-6 weeks later to assess efficacy of the drop.4 For this reason it was decided to use 6 weeks interval. All measurements were performed at The Montreal Glaucoma Institute by the same trained technician, with the same equipment and at the same time of day. Goldmann applanation tonometry was used to measure the patient’s intraocular pressure (IOP), ultrasound pachymetry was used to measure central corneal thickness (CCT) and the ORA provided the measurements of the corneal biomechanical properties, including corneal hysteresis (CH). The hypothesis of no effect regarding the discontinuation of PGA on the biomechanical properties was examined by a linear mixed-effect model using the nlme package in R. Random-effects was defined on two levels: the patient (level-1) and the eye within each patient (level-2). Those random-effects were added to the model to account for the intra-individual variance due to the repeated-measure design. Age was also included in the model as a covariate. Contrasts between the eyes and times were estimated using adjusted p-values to control for familywise error rate using multcomp package in R. Results: A statistically significant increase in CH was found between Visit 1 (on PGA) and Visit 2 (no PGA) in the study eyes, with mean (±Standard Error) values of 8.98 ± 0.29 mmHg and 10.35 ± 0.29 mmHg, respectively, corresponding to a mean increase of 1.37 ± 0.18 mmHg (p < 0.001). A significant reduction of 1.25 ± 0.18 mmHg (p < 0.001) was also observed between Visits 2 and 3, with a final mean CH value of 9.09 ± 0.29 mmHg. In addition, a statistically significant difference between the study and control eyes was only observed at Visit 2 (1.01 ± 0.23 mmHg; p < 0.001) and not at Visits 1 and 3. A statistically significant increase in Corneal Resistance Factor (CRF) was found between Visits 1 and 2 in the study eyes, with mean values of 10.23 ± 0.34 mmHg and 11.71 ± 0.34 mmHg, respectively. CRF was then reduced by 1.90 ± 0.21 mmHg (p < 0.001) between Visits 2 and 3, with a final mean CRF value of 9.81 ± 0.34 mmHg. A statistically significant difference between the study and control eyes was only observed at Visit 2 (1.46 ± 0.23 mmHg; p < 0.001). A statistically significant increase in CCT was found between Visits 1 and 2 in the study eyes, with mean values of 541.83 ± 7.27 µm and 551.91 ± 7.27 µm respectively, corresponding to a mean increase of 10.09 ± 0.94 µm (p < 0.001). CCT then decreased by 9.40 ± 0.94 µm (p < 0.001) between Visits 2 and 3, with a final mean value of 542.51 ± 7.27 µm. A difference between the study and control eyes was only recorded at Visit 2 (11.26 ± 1.79 µm; p < 0.001). Similarly, a significant increase in IOP was observed between Visits 1 and 2 in the study eyes, with mean values of 15.37 ± 0.54 mmHg and 18.37 ± 0.54 mmHg respectively, corresponding to a mean increase of 3.0 ± 0.49 mmHg (p < 0.001). A significant reduction of 2.83 ± 0.49 mmHg (p < 0.001) was observed between Visits 2 and 3, with a final mean IOP value of 15.54 ± 0.54 mmHg. The control and study eyes only differed at Visit 2 (1.91 ± 0.49 mmHg; p < 0.001), confirming the effectiveness of PGA treatment. At Visit 1, the IOP bias (IOPcc – Goldmann IOP) was similar in both groups, all eyes at that time being on long term PGA medication, with mean values of 4.1 ± 0.54 mmHg in the control eyes and 4.8 ± 0.54 mmHg in the study eyes. At Visit 2, after a 6 week washout of PGAs, the IOP bias in the tested eye was reduced to 1.6 ± 0.54 mmHg (p<0.001), meaning that underestimation of IOP by Goldmann tonometry was significantly less than at Visit 1. The difference in mean IOP bias between the study and control eyes at Visit 2, however, did not reach statistical significance (p= 0.124). A marginally significant increase of 1.53 ± 0.60 mmHg (p = 0.055) was observed between Visits 2 and 3 in the study eyes, with a final mean IOP bias value of 3.10 ± 0.54 mmHg in the study eyes and 2.8 ± 0.54 mmHg in the control eyes. We then tried to determine if a low CH was associated with signs of more severe glaucoma progression among our open-angle glaucoma patients treated with PGA. When considering all eyes on PGA at the time of the first Visit, no association was found between VF damage and CH. However, when considering only eyes with more advanced glaucoma, a significant positive correlation was observed between VF MD and CH (B = 0.65; p = 0.003). A lower CH was associated with a more negative visual field MD value and thus greater glaucoma-related damage. Conclusions: Topical prostaglandin analogs reduce CH, CRF, CCT and IOP in glaucomatous eyes. The changes in CH and CCT influence the measurement of IOP, and therefore, these changes should be taken into account when evaluating IOP lowering response to PGA medications. To discern an interaction between IOP and corneal hysteresis, further research should be conducted with intraocular pressure control. It can be achieved by using systemic medications that decrease IOP and do not influence biomechanical properties. It can also be achieved by using Pascal dynamic contour tonometry or a similar tonometer that does not depend on the biomechanical properties of the cornea. Regarding the interaction between severity of glaucoma damage and corneal hysteresis, it was demonstrated that a lower CH was associated with a more negative visual field MD value. Key Words glaucoma – prostaglandin analogs – corneal hysteresis – central corneal thickness – intraocular pressure – biomechanical properties of the cornea.

The thesis investigates methods of examining corneal biomechanics using non-contact tonometry and introduces novel techniques to investigate corneal material properties in vivo. A comprehensive systems analysis of the CorvisST (CST) and Ocular Response Analyser (ORA) was performed. Pressure sensors were used to characterisation the airflow produced by the CST and the ORA. Distinct differences were observed between the central airflow pressures between the two devices: the CST pressure was higher and of shorter duration. Scheimpflug high-speed imaging via the CST allowed components of the corneal deformation to be investigated and the development of a 3D deformation matrix (time, depth and spatial resolution) through tracing of the anterior and posterior corneal surface. Measures of whole eye movement (WEM) with CST were found to be robust. WEM demonstrated an asymmetric profile and a correction method was developed to address the corneal deformation matrix for this asymmetry. Novel methods for characterisation of intrinsic material characteristics of the cornea were developed using numerical and graphical analytical procedures. Application of these parameters was tested on enucleated porcine eyes across a wide range of manometry internal ocular pressure (MIOP). The dynamic E-Modulus was found to be most affected by MIOP change. To investigate the in vivo distribution and heterogeneity of the corneal biomechanics, a novel set-up allowed the mapping of corneal biomechanics across the cornea using the CST (central, paracentral, peripheral) and ORA (central, peripheral). Biometric and demographic grouping of subjects allowed detection of discriminating factors between individuals. The results suggest that the in vivo cornea of healthy human adults can be characterised as a viscoelastic, damped system for longitudinal strain and a highly oscillating system for lateral strain. The cornea is approximately homogenous for measures of rigidity and dynamic E-Modulus but other corneal material characteristics (longitudinal and lateral strain, hysteresis, damping and compressibility) demonstrated regional differences. The experimental design employed allowed for strict control of biometric and biomechanical intersubject variables, based on gold-standard techniques as well as newly-developed methods, thereby creating a normative database for future use.

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