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Sleep staging is a crucial step before the scoring the sleep apnoea, in subjects that are tested for this condition. These patients undergo a whole night polysomnography recording that includes EEG, EOG, ECG, EMG and respiratory signals. Sleep staging refers to the quantification of its depth. Despite the commercial sleep software being able to stage the sleep, there is a general lack of confidence amongst health practitioners of these machine results. Generally the sleep scoring is done over the visual inspection of the overnight patient EEG recording, which takes the attention of an expert medical practitioner over a couple of hours. This contributes to a waiting list of two years for patients of the Portuguese Health Service. In this work we have used a spectral comparison method called Itakura distance to be able to make a distinction between sleepy and awake epochs in a night EEG recording, therefore automatically doing the staging. We have used the data from 20 patients of Hospital Pulido Valente, which had been previously visually expert scored. Our technique results were promising, in a way that Itakura distance can, by itself, distinguish with a good degree of certainty the N2, N3 and awake states. Pre-processing stages for artefact reduction and baseline removal using Wavelets were applied.

A software tool for the analysis of the High-Resolution Electrocardiogram (HR-ECG) for Arrhythmia detection is introduced. New algorithms based on Wavelet analysis are presented and compared with the classic Simson protocol over the P and QRS segments of the Electrocardiogram (EEG). A novel procedure based on a two step wavelet analysis and synthesis is performed in order to obtain a frequency description of the P, T or QRS segments. This frequency ?signature? is useful for the detection of otherwise asymptomatic Arrhythmia patients. The tool has been developed in Matlab, and deployed for a standalone C application.

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Rail corrugation is a phenomenon that leads to a waving in the rails with wavelengths typically between 3 cm and 100 cm and amplitude levels of several microns. The genesis of this waving is complex. Rail corrugation is a recognized problem that leads to excess vibration on the rails and vehicles to a point of reducing their life span and compromising safety. In urban areas excess vibration noise is also a problem. A software tool was developed to analyze accelerometer signals acquired in the boggies of rail vehicles in order to quantify the rail corrugation according to their frequency and amplitude. A wavelet packet methodology was used in this work and compared with the One Third Octave Filter (OTOF) power representations, which is currently used in the industry. It is shown that the former produces better results.

Neste trabalho pretende-se estudar a variabilidade da frequência cardíaca através da implementação de vários métodos de análise de electrocardiogramas. Na primeira parte descrevem-se os métodos de análise espectral, bem como a representação tempo-frequência. A decomposição de sinais para detectar e isolar os batimentos cardíacos do electrocardiograma é implementada. Descrevem-se algoritmos de isolamento para detecção dos eventos interessantes e pontos fiduciais que os constituem. Na segunda parte estima-se a variação da frequência cardíaca e estabelece-se a sua relação com as variações temporais e espectrais das características encontradas pelos métodos implementados na primeira parte do trabalho.

O desenvolvimento de um pacote de software para lidar facilmente com electrocardiogramas de alta resolução tornou-se importante para pesquisa na área de electrocardiografia. O desenvolvimento de novas técnicas para detecção de potenciais tardios e outros problemas associados a arritmias cardíacas têm sido objecto de estudo ao longo dos anos. No entanto, ainda existe a lacuna de um pacote de software que facilmente permita implementar algumas destas inovadoras técnicas de uma forma integrada, possibilitando avaliar técnicas clássicas como o protocolo de Simson para a detecção de sinais não estacionários (potenciais tardios). Algumas destas inovadoras técnicas envolvem a detecção tempo-frequência usando escalogramas ou a análise espectral usando metodologias wavelet-packet, sendo implementadas no software desenvolvido com flexibilidade e versatilidade suficientes para que futuramente sirva de plataforma de pesquisa para o refinamento destas mesmas técnicas no que toca ao processamento de sinais de electrocardiogramas de alta resolução. O software aqui desenvolvido foi também desenhado de forma a suportar dois tipos de ficheiros diferentes provenientes de outros tantos sistemas de aquisição. Os sistemas suportados são o ActiveTwo da Biosemi e o USBamp da g.tec.

The time-varying microstructure of sleep EEG spindles may have clinical significance in dementia studies and can be quantified with a number of techniques. In this paper, real and simulated sleep spindles were regarded as AM?FM signals modeled by six parameters that define the instantaneous envelope (IE) and instantaneous frequency (IF) waveforms for a sleep spindle. These parameters were estimated using four different methods, namely the Hilbert transform (HT), complex demodulation (CD), matching pursuit (MP) and wavelet transform (WT). The average error in estimating these parameters was lowest for HT, higher but still less than 10% for CD and MP, and highest (greater than 10%) for WT. The signal distortion induced by the use of a given method was greatest in the case of HT and MP. These two techniques would necessitate the removal of about 0.4 s from the spindle data, which is an important limitation for the case of spindles with duration less than 1 s. Although the CD method may lead to a higher error than HT and MP, it requires a removal of only about 0.23 s of data. An application of this sleep spindle parameterization via the CD method is proposed, in search of efficient EEG-based biomarkers in dementia. Preliminary results indicate that the proposed parameterization may be promising, since it can quantify specific differences in IE and IF characteristics between sleep spindles from dementia subjects and those from aged controls.

The empirical mode decomposition (EMD) is reviewed and some questions related to its effective performance are discussed. Its interpretation in terms of AM?FM modulation is done. Solutions for its drawbacks are proposed. Numerical simulations are carried out to empirically evaluate the proposed modified EMD.