Learning non-linear time scales with Kernel γ-Filters

A family of kernel methods, based on the γ-filter structure, is presented for non-linear system identification and time series prediction. The kernel trick allows us to develop the natural non-linear extension of the (linear) support vector machine (SVM) γ-filter, but this approach yields a rigid system model without non-linear cross relation between time-scales. Several functional analysis properties allow us to develop a full, principled family of kernel γ-filters. The improved performance in several application examples suggests that a more appropriate representation of signal states is achieved.Publicad

Analysis of the Spatial Resolution of Body-Surface Dominant-Frequency Mapping Systems

Abstract In this study we assess the ability of high-density bodysurface lead systems to resolve local dominant-frequency (DF) values. In a detailed numerical model of the human thorax, we calculate the measurement sensitivity distribution (MSD) of the 117 unipolar leads of a Dalhousie lead system. Based on the MSD, we compute the lead equivalent volume (LEV) of each unipolar lead and use it to quantify the lead spatial resolution (SR). Anterior leads positioned in columns 4-6 and rows 3-5 of the Introduction Cardiac fibrillation is a complex cardiac arrhythmia whose mechanisms are not well understood. In the past years, intracardiac dominant-frequency (DF) mapping has enhanced the understanding of the mechanisms of cardiac fibrillation and has been used as a guide for atrial fibrillation (AF) ablation therapies The correlation between intracardiac and body-surface DF values during AF suggests that body-surface DF maps may be used as surrogates for intracardiac DF maps. Nevertheless, the detailed correspondence between intracardiac and body-surface DF values remains to date unclear. It is assumed that intracardiac and body-surface leads have different spatial resolution (SR) values. Due to their proximity to the myocardium, intracardiac leads mostly measure local activity. By contrast, body-surface leads measure global activity, since they are located further away from the myocardium. This discrepancy between intracardiac and body-surface SR values could potentially prevent the existence of a ono-te-one correspondence between intracardiac and body-surface DF values. The reasons are twofold. Firstly, global body-surface DF values would not reflect local DF values, but rather an average over the SR The measurement sensitivity distribution (MSD), also known as lead field, has been used to study the properties of different lead systems. In a classical work by Rush and Driscoll, the MSD of electroencephalographic (EEG) leads was analyzed cinc.org Computing in Cardiology 2012; 39:345-348

An Analytical Model for the Effects of the Spatial Resolution of Electrode Systems on the Spectrum of Cardiac Signals

It has been suggested that the spatiotemporal characteristics of complex cardiac arrhythmias can be extracted from the spectrum of cardiac signals. However, the analysis of simple bioelectric models indicates that the spectrum of cardiac signals can be affected by the spatial resolution of the electrode system. In this study, we derive exact measurement transfer functions relating the spectrum of cardiac signals to the spatiotemporal dynamics of cardiac sources and estimate their bandwidths. The analysis of the measurement transfer bandwidths for dynamics with different degrees of spatiotemporal correlation shows that as the spatial resolution decreases, the bandwidth of the measurement transfer function decreases until it reaches a constant value. Moreover, this transition from decreasing to constant values is determined by the degree of spatiotemporal correlation of the underlying cardiac source. Motivated by our analytical results, we investigate in a realistic computer simulation environment the impact of additive noise on the accuracy of body-surface dominant frequency (DF) maps. Our simulation results show that meaningful DF values are obtained on those locations where the analytical measurement transfer bandwidth is wide. These findings suggest that the accuracy of body-surface DF maps can be limited by the low spatial resolution of body-surface electrode systems

Applications of Serious Games as Affective Disorder Therapies in Autistic and Neurotypical Individuals: A Literature Review

Affective disorders can greatly influence the everyday lives of neurotypical and autistic individuals. As platforms that promote engagement, computer-based serious games (CSGs) have been previously proposed as therapies to treat affective disorders for both populations. However, these CSGs were assessed on a wide variety of experimental conditions, and there is a lack of comparative studies on their effectiveness. In this study, we identified and analyzed 37 interventions of CSGs for affective disorders in autistic and neurotypical individuals from 507 initial search results from four databases (Embase, Scopus, Web Of Science and IEEE Xplore), using concepts such as 'serious-games', 'affective-disorders', 'autism' and 'neurotypical'. A total of 21 different CSGs were identified that were evaluated with 30 different outcome measures in the reviewed interventions. A positive impact was reported in 22 of them; specifically, all instances of depression interventions reported a positive impact of CSG therapies. Our comparative analysis indicates that CSG applications could be effective in treating affective disorders in autistic and neurotypical individuals. Additionally, our analysis identifies CSG design characteristics that might be useful in applications involving depression, anxiety and phobias. Based on these characteristics, we provide a set of recommendations for CSG interventions for affective disorder therapies

Desarrollo de un modelo probabilístico de la actividad eléctrica cardíaca basado en un autómata celular

Introducción y objetivos. La utilización de modelos matemáticos de activación y propagación del impulso ha mejorado la comprensión de diversos mecanismos electrofisiológicos involucrados en la génesis de las arritmias. Las simulaciones más realistas se basan en los modelos de reacción-difusión e implican una carga computacional muy elevada. El objetivo del estudio es desarrollar un modelo de activación eléctrica cardíaca por ordenador que permita simular fenómenos electrofisiológicos complejos y que no requiera la carga computacional necesaria en otros modelos habitualmente empleados. Material y método. Se ha modelado el tejido cardíaco como un autómata celular, cada uno de cuyos elementos adopta estados discretos en función de su estado previo y del de las células vecinas siguiendo unas reglas sencillas. La activación se contempla como un proceso probabilístico y se ajusta mediante el fenómeno de restitución, mientras la repolarización se modela como un proceso determinista. Finalmente, las corrientes celulares se calculan utilizando un potencial de acción prototipo, lo que permite simular los electrogramas virtuales monopolares y bipolares en cualquier punto del espacio. Resultados. Se ha conseguido reproducir frentes planos de activación, propagación de un estímulo focal y reentradas estables e inestables en 2 dimensiones, con sus electrogramas correspondientes. El modelo es particularmente adecuado para simular los fenómenos asociados a la curvatura de los frentes, y permite reproducir la conducción fibrilatoria y los rotores estables en 2 y 3 dimensiones. Conclusiones. Aunque el modelo de autómata celular probabilístico desarrollado es sencillo y no requiere cargas computacionales elevadas, es capaz de simular de forma realista fenómenos complejos de gran interés en electrofisiología

El incremento temprano de la frecuencia cardíaca no predice el resultado de la prueba de basculación potenciada con nitroglicerina

Introducción y objetivos. El incremento acentuado de la frecuencia cardíaca en los primeros minutos de la prueba de basculación ha sido utilizado como predictor del resultado final de ésta, en protocolos sin potenciación farmacológica o con isoproterenol. El objetivo del estudio es evaluar si este incremento se relaciona con la aparición de síncope durante la prueba de basculación potenciada con nitroglicerina. Pacientes y método. Análisis retrospectivo de 158 pacientes consecutivos sometidos a prueba de basculación potenciada con nitroglicerina por síncope, sin cardiopatía y en ritmo sinusal. Se calculó el incremento de la frecuencia cardíaca secundario a la basculación y el debido a la nitroglicerina, relacionándolos con las variables clínicas y el resultado de la prueba. Resultados. La prueba de basculación fue positiva en 117 pacientes (74%). La frecuencia cardíaca pasó de 68,7 ± 11,3 lat/min en decúbito a 85,1 ± 15,4 lat/min en los primeros 6 min posbasculación. El incremento de frecuencia presentó una fuerte correlación negativa con la edad (r = ­-0,63; p < 0,001), pero no se relacionó significativamente con el resultado (16,8 ± 9,3 lat/min en el grupo con prueba positiva frente a 14,9 ± 11,3 en el negativo; p = 0,3). El aumento de la frecuencia cardíaca inducido por la nitroglicerina (27,3 ± 12,6 y 26,7 ± 13,4 lat/min, respectivamente; p = 0,8) tampoco predijo el resultado del test durante la fase farmacológica. Conclusiones. Los incrementos de frecuencia cardíaca en los primeros minutos después de la basculación y la administración del fármaco se relacionan fundamentalmente con la edad y no tienen utilidad para predecir el resultado de la prueba de basculación potenciada con nitroglicerina