Integración numérica de problemas de trayectorias

Llamamos problema de trayectorias al consistente en la determinación de la curva que describe en el espacio de las fases la solución de un problema de Cauchy para un sistema autónomo de ecuaciones diferenciales ordinarias. Presentamos la formulación, estudio del error de truncación local en función de elementos geométricos de la curva y experimentación numérica de varios métodos en diferencias finitas específicamente diseñados para la integración numérica de ese problema.Peer Reviewe

Low level and high frequency fragmentation of the QRS changes during acute myocardial ischemia in patients with and without prior myocardial infarction

High frequency (HF) QRS fragmentation and very-low amplitude abnormal intra-QRS potential (uAIQP) analyses have been used to track ischemic changes during coronary artery occlusions. The aim of this study was to assess the relationship between these two techniques in detecting acute myocardial ischemia and the effects of a previous myocardial infarction (MI). Fifty-six patients who underwent elective percutaneous coronary intervention (PCI) procedures were selected and classified into 2 groups according to the presence of prior healed MI (old-MI) (n=18) or not (no_MI) (n=38). Continuous ECG before and during the PCI were recorded and signal-averaged. uAIQPs were obtained using a signal modelling approach. HFQRSRMS was obtained by band pass filtering the ECGs at 150 to 250 Hz. QRS-HFpower was estimated from a modeling power spectral technique. uAIQP and HF indices were obtained from a baseline and an occlusion-PCI ECG episode. uAIQP and HF values decreased (p<0.05) for each of the 12 leads at the PCI event respect to baseline in all patients and the no-MI group. Changes in uAIQP or HF did not separate the groups. uAIQP and QRS-HFpower values at baseline were lower in all leads, except V1-V2, in the old-MI groups compared to no-MI (p<0.05). Pearson’s correlation showed moderate relationship among the indices in most of leads. High-frequency QRS fragmentation indices could add diagnostic value to ST analysis for diagnosing ischemia when a baseline ECG information is available. Patients with old-MI presented lower uAIQP amplitudes compared to no-MI, however further studies are needed to elucidate the effects of old MI on very-low level fragmentation of the QRS.Peer ReviewedPostprint (published version

Caracterización de pacientes con diferentes niveles de riesgo cardiovascular mediante diagramas de Poincaré

En este trabajo se propone caracterizar la dinámica no-lineal de los sistemas cardíaco, vascular y respiratorio a partir de los diagramas de Poincaré. Se han analizado 46 pacientes con cardiomiopatía isquémica (ICM) o dilatada (DCM), y 35 sujetos sanos. De acuerdo con su fracción de eyección ventricular izquierda (LVEF), los pacientes también fueron clasificados en un grupo de alto riesgo (HR: LVEF = 35%, 30 pacientes) y otro de bajo riesgo (LR: LVEF > 35%, 16 pacientes). A partir de las señales electrocardiográfica, de flujo respiratorio y de presión sanguínea se han obtenido los datos relacionados con el tiempo entre latidos cardíacos (RR), entre valores máximos de presión sistólica (SBP), y la duración del ciclo respiratorio (TTot). Estas series temporales han sido representadas mediante los diagramas de Poincaré, y caracterizadas teniendo en cuenta su desviación a largo plazo (SD1) y su cambio instantáneo (SD2). De acuerdo con los resultados obtenidos, los parámetros de las series cardíaca y de presión sanguínea, relacionados con las diagonales longitudinales y transversales del diagrama de Poincaré, son los que mejor diferencian entre pacientes con HR vs LR. Para la clasificación de pacientes isquémicos vs dilatados, los mejores parámetros se obtuvieron a partir de las series respiratorias y están relacionados con las distancias de la desviación estándar a la línea de identidad. Los cambios en estas relaciones representan una mayor aceleración en la dinámica respiratoria de los pacientes con cardiomiopatía isquémica.Postprint (published version

Use of Gene Ontology semantic information in protein interaction data visualization

The Gene Ontology project is an effort to structure knowledge on biological products and processes by adding semantic information to them. This is done in a systematic way so that this additional information can be automatically processed. In this contribution a protein-protein interaction visualization algorithm is proposed, which combines protein interaction data with Gene Ontology semantic information. The information is integrated using a semantic distance measure defined in ontologies or taxonomies. Multidimensional scaling is applied to this measure and the output complements protein interaction data in building an interaction visualization map.Peer ReviewedPostprint (published version

La Recerca en bioenginyeria cardíaca i pulmonar a l'Institut de Cibernètica

En aquesta ponència presentem els treballs de recerca duts a terme els darrers anys a l'Institut de Cibernètica en el camp de la bioenginyeria. Cal destacar la simulació en computador híbrid del sistema càrdio-vascular, l'anàlisi i caracterització de pròtesis valvulars cardíaques i el processament automàtic de l'electrocardiograma del feix de His, dins l'àrea de la bioenginyeria cardíaca. La recerca en bioenginyeria pulmonar ha estat centrada en el disseny d'equips que col•laboren en 1'exploració funcional pulmonar.This paper presents the bioengineering research carried out at the Institut de Cibernètica the last years. We can remark the cardiovascular system simulation by hybrid computer, the prosthetic cardiac valves characterization, the His bundle electrogram on-line processing and different devices developed to explore the pulmonary function

Filtering and thresholding the analytic signal envelope in order to improve peak and spike noise reduction in EEG signals

To remove peak and spike artifacts in biological time series has represented a hard challenge in the last decades. Several methods have been implemented mainly based on adaptive filtering in order to solve this problem. This work presents an algorithm for removing peak and spike artifacts based on a threshold built on the analytic signal envelope. The algorithm was tested on simulated and real EEG signals that contain peak and spike artifacts with random amplitude and frequency occurrence. The performance of the filter was compared with commonly used adaptive filters. Three indexes were used for testing the performance of the filters: Correlation coefficient, mean of coherence function, and rate of absolute error. All these indexes were calculated between filtered signal and original signal without noise. It was found that the new proposed filter was able to reduce the amplitude of peak and spike artifacts with > 0.85, C > 0.8, and RAE 1)

Estudio de la potencia de la inspiración como predictor del proceso de extubación en pacientes

La extubación de pacientes asistidos mediante ventilación mecánica sigue siendo un proceso fundamental en la práctica clínica, de especial atención en las unidades de cuidados intensivos. En este estudio se propone un nuevo índice de extubación basado en la potencia de la señal de flujo respiratorio (Pi). Se estudiaron un total de 132 pacientes sometidos al proceso de destete: 94 pacientes (GE) con resultado de éxito en la prueba, y 38 pacientes (GF) que fracasaron en el proceso de destete y tuvieron que ser reconectados al ventilador mecánico. La señal de flujo respiratorio fue procesada para obtener la potencia de la fase inspiratoria, considerando las siguientes etapas: a) detección del cruce por cero, b) detección del punto de inflexión, y c) obtención de la potencia de la señal hasta dicho punto. La detección de cruce por cero se realizó utilizando un algoritmo basado en umbrales. Los puntos de inflexión fueron marcados teniendo en cuenta el cero de la segunda derivada. La potencia de la fase inspiratoria se calculó a partir de la energía de la señal desde el cruce por cero hasta el punto de máxima inflexión. El nuevo índice fue evaluado como estimador de éxito en la extubación. Los resultados fueron analizados utilizando clasificadores como regresión logística, análisis discriminante lineal, árboles de decisión, teoría bayesiana, y máquinas de soporte vectorial. Los clasificadores Bayesianos presentaron los mejores resultados con una exactitud del 87%, y sensibilidad y especificidad de 90% y 81%, respectivamente.Postprint (published version

Search of phenotype-related candidate genes using Gene Ontology-based semantic similarity and protein interaction information: application to Brugada syndrome

This work presents a methodology for finding phenotype candidate genes starting from a set of known related genes. This is accomplished by automatically mining and organizing the available scientific literature using Gene Ontology-based semantic similarity. As a case study, Brugada syndrome related genes have been used as input in order to obtain a list of other possible candidate genes related with this disease. Brugada anomaly produces a typical alteration in the Electrocardiogram and carriers of the disease show an increased probability of sudden death. Results show a set of semantically coherent proteins that are shown to be related with synaptic transmission and muscle contraction physiological processes.Peer ReviewedPostprint (published version

Analysis of ECG in athletes running in mountain route conditions

The purpose of this work is to analyse changes in ECG and heart rate variability (HRV) metrics in athletes during 10 km running in mountain route conditions. Eighteen healthy athletes carrying a 12-lead ECG GE Holter recorder and a heart rate monitor ran a route with slopes similar as trail races. QRS duration, QRS area, R-wave peak, ST elevation at J-point and J+60 ms, ST slope and T-wave peak indices were computed after signal-averaging ECG segments at different sloping stages of running (S1-S6) and at a control stage (S0) before running. HRV analysis included standard time and frequency metrics: mean RR (normal, N) interval, SDNN, RMSSD, low and high frequency absolute and normalized power (LF, HF, LFn, HFn) and LF/HF ratio. QRS area and R-peak were reduced during stage 1 in lateral leads, comparing to rest before running. ST slope was significantly higher during upslope stages in leads II, V4 and V5. T-wave amplitude increased significantly in precordial leads during upload running. ST segment depressed in leads II, III and V5 respect control. Mean RR, SDNN, LF and LFn showed high significant differences (p<0.01) among stages and HF and LF/HF were also varying (p<0.05). Changes of ECG and HRV indices can help understanding the cardiac function in runners performing extreme stress.Postprint (published version

Measuring instantaneous and spectral information entropies by shannon entropy of choi-williams distribution in the context of electroencephalography

The theory of Shannon entropy was applied to the Choi-Williams time-frequency distribution (CWD) of time series in order to extract entropy information in both time and frequency domains. In this way, four novel indexes were defined: (1) partial instantaneous entropy, calculated as the entropy of the CWD with respect to time by using the probability mass function at each time instant taken independently; (2) partial spectral information entropy, calculated as the entropy of the CWD with respect to frequency by using the probability mass function of each frequency value taken independently; (3) complete instantaneous entropy, calculated as the entropy of the CWD with respect to time by using the probability mass function of the entire CWD; (4) complete spectral information entropy, calculated as the entropy of the CWD with respect to frequency by using the probability mass function of the entire CWD. These indexes were tested on synthetic time series with different behavior (periodic, chaotic and random) and on a dataset of electroencephalographic (EEG) signals recorded in different states (eyes-open, eyes-closed, ictal and non-ictal activity). The results have shown that the values of these indexes tend to decrease, with different proportion, when the behavior of the synthetic signals evolved from chaos or randomness to periodicity. Statistical differences (p-value < 0.0005) were found between values of these measures comparing eyes-open and eyes-closed states and between ictal and non-ictal states in the traditional EEG frequency bands. Finally, this paper has demonstrated that the proposed measures can be useful tools to quantify the different periodic, chaotic and random components in EEG signals. © 2014 by the authors; licensee MDPI, Basel, Switzerland.Peer ReviewedPostprint (published version