A dinâmica em meso-escala nos oceanos globais é dominada por sinais propagantes para oeste. Estudos pioneiros a utilizar medidas de altimetria por satélites associaram este sinal a ondas de Rossby longas do primeiro modo baroclínico. Com o recente aumento de resolução nos dados altimétricos, estudos mais recentes sugerem que vórtices de meso-escala não-lineares seriam os principais responsáveis pelo sinal propagante observado, em detrimento às ondas de Rossby. O objetivo do presente trabalho é identificar estruturas coerentes associadas a vórtices de meso-escala e distingui-las das ondas de Rossby longas do primeiro modo baroclínico. Mapas de anomalia da altura da superfície do mar (η) foram filtrados através da análise de ondaletas e um algoritmo de identificação e extração de estruturas vorticais. Os vórtices extraídos foram caracterizados através do ajuste de um paraboloide elíptico. O algoritmo demonstrou-se capaz de identificar e extrair as estruturas associadas a vórtices de meso-escala. Os resultados indicam predominância de anéis vorticais anti-ciclônicos. Os espectros de potência zonais-temporais de η indicam que a maior parte da variância distribui-se na região não-dispersiva do espectro teórico de ondas de Rossby lineares. A propagação observada nos componentes resultantes do filtro indicam coexistência de ondas de Rossby lineares e vórtices de meso-escala, comprovando assim a hipótese científica estabelecida para este trabalho. / The mesoscale dynamics in the global oceans is dominated by westward propagating signals. Pioneering studies using satellite altimetry measurements associated these observations with first-mode baroclinic Rossby waves. With the increase in altimetry data resolution, recent studies suggest that nonlinear mesoscale eddies are responsible for the westward propagating signal rather than Rossby waves. The objective of this study is to identify coherent structures associated with mesoscale eddies and distinguish them from long first-mode baroclinic Rossby waves. Sea surface height anomaly maps (η) were filtered throught wavelet analysis and an algorithm for identifying and extracting vortical structures. The extracted vortices were characterized by adjusting an elliptic paraboloid. The algorithm proved to be able to identify and extract the structures associated to mesoscale eddies. The results indicate a predominance of anti-cyclonic rings. Zonal-temporal power spectral density of η indicate that most of the variance is located at the non-dispersive region of the theoretical linear Rossby wave spectra. The observed propagation of the filtered components indicate coexistence of linear Rossby waves and mesoscale eddies, thus proving the scientific hypothesis of this study.

A dinâmica em meso-escala nos oceanos globais é dominada por sinais propagantes para oeste. Estudos pioneiros a utilizar medidas de altimetria por satélites associaram este sinal a ondas de Rossby longas do primeiro modo baroclínico. Com o recente aumento de resolução nos dados altimétricos, estudos mais recentes sugerem que vórtices de meso-escala não-lineares seriam os principais responsáveis pelo sinal propagante observado, em detrimento às ondas de Rossby. O objetivo do presente trabalho é identificar estruturas coerentes associadas a vórtices de meso-escala e distingui-las das ondas de Rossby longas do primeiro modo baroclínico. Mapas de anomalia da altura da superfície do mar (η) foram filtrados através da análise de ondaletas e um algoritmo de identificação e extração de estruturas vorticais. Os vórtices extraídos foram caracterizados através do ajuste de um paraboloide elíptico. O algoritmo demonstrou-se capaz de identificar e extrair as estruturas associadas a vórtices de meso-escala. Os resultados indicam predominância de anéis vorticais anti-ciclônicos. Os espectros de potência zonais-temporais de η indicam que a maior parte da variância distribui-se na região não-dispersiva do espectro teórico de ondas de Rossby lineares. A propagação observada nos componentes resultantes do filtro indicam coexistência de ondas de Rossby lineares e vórtices de meso-escala, comprovando assim a hipótese científica estabelecida para este trabalho. / The mesoscale dynamics in the global oceans is dominated by westward propagating signals. Pioneering studies using satellite altimetry measurements associated these observations with first-mode baroclinic Rossby waves. With the increase in altimetry data resolution, recent studies suggest that nonlinear mesoscale eddies are responsible for the westward propagating signal rather than Rossby waves. The objective of this study is to identify coherent structures associated with mesoscale eddies and distinguish them from long first-mode baroclinic Rossby waves. Sea surface height anomaly maps (η) were filtered throught wavelet analysis and an algorithm for identifying and extracting vortical structures. The extracted vortices were characterized by adjusting an elliptic paraboloid. The algorithm proved to be able to identify and extract the structures associated to mesoscale eddies. The results indicate a predominance of anti-cyclonic rings. Zonal-temporal power spectral density of η indicate that most of the variance is located at the non-dispersive region of the theoretical linear Rossby wave spectra. The observed propagation of the filtered components indicate coexistence of linear Rossby waves and mesoscale eddies, thus proving the scientific hypothesis of this study.

To track evolution of autonomic responses during orthostasis in men and women, we used discrete pseudo-Wigner distribution based time-frequency analysis to compute dominant frequencies and spectral powers in RR intervals and Systolic Blood Pressure (SBP). Data were collected from 38 healthy volunteers (22 men, 16 women) during 10 min supine posture followed by 30 min of 700 head up tilt. The RR intervals were computed from ECG and systolic blood pressure was and spectral amplitudes of RR intervals were integrated in two regions viz., Low Frequency (LF) region defined between 0.05-0.15 Hz and High Frequency region (HF), sometimes referred to as respiratory frequency region, defined as mean breathing frequency of the individual +/- one standard deviation. Dominant frequencies of RR intervals in the LF region decreased in both men and women. There were no significant differences between men and women as far as the SBP data were concerned for the dominant frequencies, however women had higher values than men. Dominant frequencies of RR intervals in the HF region increased both in men and women from supine to tilt. No significant differences in dominant frequencies were found between men and women. Also there were no significant differences even for the SBP data, however men had higher values than women Integrated powers within the auto spectra of RR showed that in the HF region, power decreased significantly for both men (pandlt;0.005), and women (pandlt;0.001) during tilt compared to supine. However, the HF power in women was significantly higher for men during both supine (pandlt;0.001), and tilt (pandlt;0.005). In LF region integrated power spectrum showed no significant difference between men and women although women showed a slight increase from supine to tilt. These results suggest that men have a higher sympathetic control while women have greater para-sympathetic influence.

Noninvasive assessment of diabetic cardiovascular autonomic neuropathy (AN): Cardiac and vascular dysfunctions resulting from AN are complications of diabetes, often undiagnosed. Our objectives were to: 1) determine sympathetic and parasympathetic components of compromised blood pressure regulation in patients with polyneuropathy, and 2) rank noninvasive indexes for their sensitivity in diagnosing AN. Continuous 12-lead electrocardiography (ECG), blood pressure (BP), respiration, regional blood flow and bio-impedance were recorded from 12 able-bodied subjects (AB), 7 diabetics without (D0), 7 with possible (D1) and 8 with definite polyneuropathy (D2), during 10 minutes supine control, 30 minutes 70-degree head-up tilt and 5 minutes supine recovery. During the first 3 minutes of tilt, systolic BP decreased in D2 while increased in AB. Parasympathetic control of heart rate, baroreflex sensitivity, and baroreflex effectiveness and sympathetic control of heart rate and vasomotion were reduced in D2, compared with AB. Baroreflex effectiveness index was identified as the most sensitive index to discriminate diabetic AN. Four-dimensional multiscale modeling of ECG indexes of diabetic autonomic neuropathy: QT interval prolongation which predicts long-term mortality in diabetics with AN, is well known. The mechanism of QT interval prolongation is still unknown, but correlation of regional sympathetic denervation of the heart (revealed by cardiac imaging) with QT interval in 12-lead ECG has been proposed. The goal of this study is to 1) reproduce QT interval prolongation seen in diabetics, and 2) develop a computer model to link QT interval prolongation to regional cardiac sympathetic denervation at the cellular level. From the 12-lead ECG acquired in the study above, heart rate-corrected QT interval (QTc) was computed and a reduced ionic whole heart mathematical model was constructed. Twelve-lead ECG was produced as a forward solution from an equivalent cardiac source. Different patterns of regional denervation in cardiac images of diabetic patients guided the simulation of pathological changes. Minimum QTc interval of lateral leads tended to be longer in D2 than in AB. Prolonging action potential duration in the basal septal region in the model produced ECG and QT interval similar to that of D2 subjects, suggesting sympathetic denervation in this region in patients with definite neuropathy.

No description available.

Alzheimer’s is one of the most costly illnesses that exists today and the number of people with alzheimers diease is expected to increase with 100 million until the year 2050. The medication that exists today is most effective if Alzheimer’s is detected during early stages since these medications do not cure Alzheimer’s but slows down the progression of the disease. Electroencephalography (EEG) is a relatively cheap method in comparison to for example Magnetic Resonance Imaging when it comes to diagnostic tools. However it is not clear how to deduce whether a patient has Alzheimer’s disease just from EEG data when the analyst is a human. This is the underlying motivation for our investigation; can supervised machine learning methods be used for pattern recognition using only the spectral power of EEG data to tell whether an individual has alzheimer’s disease or not? The output accuracy of the trained supervised machine learning models showed an average accuracy of above 80%. This indicates that there is a difference in the neural oscillations of the brain between healthy individuals and alzheimer’s disease patients which the machine learning methods are able to detect using pattern recognition. / Alzheimer är en av de mest kostsamma sjukdomar som existerar idag och antalet människor med alzheimer förväntas öka med omkring 100 miljoner människor tills 2050. Den medicinska hjälp som finns tillgänglig idag är som mest effektiv om man upptäcker Alzheimer i ett tidigt stadium eftersom dagens mediciner inte botar sjukdomen utan fungerar som bromsmedicin. Elektroencefalografi är en relativt billig metod för diagnostisering jämfört med Magnetisk resonanstomografi. Det är emellertid inte tydligt hur en läkare eller annan tränad individ ska tolka EEG datan för att kunna avgöra om det är en patient med alzheimers som de kollar på. Så den bakomliggande motivation till vår undersökning är; Kan man med hjälp av övervakad maskininlärning i kombination med spektral kraft från EEG datorn skapa modeller som kan avgöra om en patient har alzheimers eller inte. Medelvärdet av våra modellers noggrannhet var över 80%. Detta tyder på att det finns en faktiskt skillnad mellan hjärna signalerna hos en patient med alzheimer och en frisk individ, och att man med hjälp av maskininlärning kan hitta dessa skillnader som en människa enkelt missar.

Bien que l’anesthésie générale soit un outil indispensable dans la chirurgie médicale d’aujourd’hui, ses mécanismes sous-jacents précis sont encore inconnus. Au cours de la sédation induite par le propofol les actions anesthésiques à l’échelle microscopique du neurone isolé conduisent à des changements spécifiques à l’échelle macroscopique qui sont observables comme les signaux électroencéphalogrammes (EEG). Pour une concentration faible en propofol, ces changements caractéristiques comprennent une augmentation de l’activité dans les bandes de fréquence delta (0.5-4 Hz) et alpha (8 13 Hz) dans la région frontal, une l’activité augmentée de delta et une l’activité diminuée de alpha dans la région occipitale. Dans cette thèse, nous utilisons des modèles de populations neuronales thalamo-corticales basés sur des données expérimentales. Les effets de propofol sur les synapses et sur les récepteurs extra-synaptiques GABAergiques situés dans le cortex et le thalamus sont modélisés afin de comprendre les mécanismes sous-jacents aux changements observés dans certaines puissances de l’EEG spectrale. Il est démontré que les modèles reproduisent bien les spectrales caractéristiques observées expérimentalement. Une des conclusions principales de ce travail est que l’origine des delta rythmes est fondamentalement différente de celle des alpha rythmes. Nos résultats indiquent qu’en fonction des valeurs moyennes des potentiels de l’état du système au repos, une augmentation ou une diminution des fonctions de gain thalamo-corticale résulte respectivement en une augmentation ou une diminution de alpha puissance. En revanche, l’évolution de la delta puissance est plutôt indépendant de l’état du système au repos; l'amélioration de la puissance spectrale de delta bande résulte de l’inhibition GABAergique synaptique ou extra-synaptique pour les fonctions de gain non linéaire à la fois croissante et décroissante. De plus, nous cherchons à identifier les paramètres d’un modèle de thalamo-corticale en ajustant le spectre de puissance de modèle pour les enregistrements EEG. Pour ce faire, nous considérons la tâche de l’estimation des paramètres dans les modèles qui sont décrits par un ensemble d’équations différentielles ordinaires ou bien stochastiques avec retard. Deux études de cas portant sur des données pseudo-expérimentales bruyantes sont d’abord effectuées pour comparer les performances des différentes méthodes d’optimisation. Les résultats de cette élaboration montrent que la méthode utilisée dans cette étude est capable d’estimer avec précision les paramètres indépendants du modèle et cela nous permet d’éviter les coûts de calcul des intégrations numériques. En considérant l’ensemble, les conclusions de cette thèse apportent de nouveaux éclairages sur les mécanismes responsables des changements spécifiques qui sont observées pendant la sédation propofol-induite dans les modèles de EEG. / Although general anaesthesia is an indispensable tool in today’s medical surgery, its precise underlying mechanisms are still unknown. During the propofol-induced sedation, the anaesthetic actions on the microscopic single neuron scale lead to specific changes in macroscopic-scale observables such as electroencephalogram (EEG) signals. For low concentration of propofol these characteristic changes comprised increased activity in the delta (0.5-4 Hz) and alpha (8-13 Hz) frequency bands over the frontal head region, but increased delta and decreased alpha power activity over the occipital region. In this thesis, we employ thalamo-cortical neural population models, and based on the experimental data, the propofol effects on the synaptic and extrasynaptic GABAergic receptors located in the cortex and thalamus are modelized to understand the mechanisms underlying the observed certain changes in EEG-spectral power. It is shown that the models reproduce well the characteristic spectral features observed experimentally. A key finding of this work is that the origin of delta rhythm is fundamentally different from the alpha rhythm. Our results indicate that dependent on the mean potential values of the system resting states, an increase or decrease in the thalamo-cortical gain functions results in an increase or decrease in the alpha power, respectively. In contrast, the evolution of the delta power is rather independent of the system resting states; the enhancement of spectral power in the delta band results from the increased synaptic or extra-synaptic GABAergic inhibition for both increasing and decreasing nonlinear gain functions. Furthermore, we aim to identify the parameters of a thalamo-cortical model by fitting the model power spectrum to the EEG recordings. To this end, we address the task of parameter estimation in the models that are described by a set of stochastic ordinary or delay differential equations. Two case studies dealing with noisy pseudo-experimental data are first carried out to compare the performance of different optimization methods. The results of this elaboration show that the method used in this study is able to accurately estimate the independent model parameters while it allows us to avoid the computational costs of the numerical integrations. Taken together, the findings of this thesis provide new insights into the mechanisms responsible for the specific changes in EEG patterns that are observed during propofol-induced sedation.

Le trouble comportemental en sommeil paradoxal idiopathique (TCSPi) précède de plusieurs années le diagnostic d’une maladie synucléinopathique. Dans cette étude, nous cherchions à déterminer si la puissance spectrale relative, les composantes rythmiques et arythmiques des spectres de puissance, ainsi que la connectivité fonctionnelle permettaient d’identifier à un temps de base les patients ayant un TCSPi qui développerait une synucléinopathie lors des suivis cliniques annuels. Un enregistrement EEG au repos et une évaluation neuropsychologique ont été conduits auprès de quatre-vingt-un participants atteints d’un TCSPi (66.89 ± 6.91 ans, 20 femmes) et des évaluations neurologiques annuelles étaient menées afin de définir si les patients montraient des symptômes d’une maladie synucléinopathique. La puissance spectrale standard ainsi qu’une estimation spectrale des composantes rythmiques et arythmiques ont été calculées. Ensuite, la connectivité fonctionnelle globale et entre chaque paire d’électrodes ont été estimée par le weighted Phase Lag Index. Après une durée de suivi de 5.01 ± 2.76 ans, 34 participants ont été diagnostiqués avec une synucléinopathie et 47 sont restés exempts de maladie. Comparativement aux participants avec un TCSPi n’ayant pas converti, ceux ayant converti montraient, lors de l’évaluation de base, une puissance spectrale relative plus élevée dans la bande thêta, une pente de la composante arythmique plus abrupte ainsi qu'une puissance rythmique plus élevée en thêta dans les régions occipitales et temporales ainsi qu’en en bêta1 dans les régions frontales. De plus, les patients TCSPi ayant converti présentaient une hyperconnectivité globale dans la bande bêta, mais une hypoconnectivité dans la bande alpha entre les régions temporo-occipitales gauches lors de l’évaluation de base comparativement à ceux n’ayant pas converti. Les altérations mesurables en EEG au repos lors de l’évaluation de base chez les participants avec TCSPi ayant converti vers une maladie synucléinopathique suggèrent une perturbation des réseaux à grande échelle affectés par la neurodégénérescence précoce des structures sous-corticales. / Idiopathic REM sleep behavior disorder (iRBD) precedes the diagnosis of synucleinopathies by several years. In this study, we aimed to determine whether relative spectral power, rhythmic and arrhythmic components of power spectra, and functional connectivity at baseline could identify patients with iRBD who will develop a synucleinopathy at follow-up. Resting-state EEG recordings and neuropsychological evaluations were conducted on eighty-one participants with iRBD (66.89 ± 6.91 years; 20 women), and annual neurological assessments were performed to define the emergence of synucleinopathy symptoms. Standard spectral power and spectral estimates of rhythmic and arrhythmic components were calculated. Additionally, global and pairwise functional connectivity were estimated using the weighted Phase Lag Index. After a follow-up period of 5.01 ± 2.76 years, 34 participants were diagnosed with a synucleinopathic disorder, while 47 remained disease-free. Compared to patients who did not convert, patients who converted at follow-up exhibited higher relative spectral power in the theta band, steeper slopes of the arrhythmic component, and increased rhythmic power in theta in posterior regions and beta1 in frontal regions at baseline evaluation. Furthermore, participants who converted showed hyperconnectivity in the beta band and hypoconnectivity in the alpha band between left temporo-occipital regions at baseline compared to participants who did not convert. The measurable alterations in resting-state EEG at baseline in participants with iRBD who phenoconverted towards a synucleinopathy suggest disruption of large-scale networks affected by early neurodegeneration of subcortical structures.

The thesis focuses on the issue of signal processing. Using practical examples, it tries to show the use of individual signal processing operations from a practical point of view. For each of the selected signal processing operations, an application is created in MATLAB, including a graphical interface for easier operation. The division of the thesis is such that each chapter is first analyzed from a theoretical point of view, then it is shown using a practical demonstration of what the operation is used in practice. Individual applications are described here, mainly in terms of how they are handled and their possible results. The results of the practical part are presented in the attachment of the thesis.