Examinando por Autor "Mora Jimenez, I"

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Analysis of Physiological Meaning of Detrended Fluctuation Analysis in Heart Rate Variability Using a Lumped Parameter Model
(2009-06-15T10:04:05Z) Rojo-Álvarez, José Luis; Sánchez Sánchez, A; Barquero Pérez, Óscar; Goya Esteban, R; Everss, E; Mora Jimenez, I; García Alberola, A
Chaos and fractal based measurements, such as Detrended Fluctuation Analysis (DFA), have been widely used for quantifying the Heart Rate Variability (HRV) for cardiac risk stratification purposes. However, the physiological meaning of these measurements is not clear. Given that existing lumped parameter models contain a detailed physiological description of several of the circulatory system regulation processes, we hypothesize that controlled changes in these processes will highlight the physiological basis in DFA indices. We used a detailed lumped parameter model of HRV, introduced earlier [6]. Ten signals were generated in different physiological conditions. DFA coefficients 1, 2, and the Hurst exponent, were calculated. A clear disruption point was always observed. Modifications in sympatho-vagal activity yielded significant changes in 1 when compared to basal, but not in 2 or Hurst exponent. Modifications in non-nervous system mediated changes yielded significant differences only for peripheral resistance and heart period, only in 1. In conclusion, the analysis of the effect of changes in the regulatory system on the HRV chaotic/fractal indices can be analyzed using detailed lumped parameter models
Detection and Estimation of T Wave Alternans with Matched Filter and Nonparametric Bootstrap Test
(2009-06-15T09:07:17Z) Rojo-Álvarez, José Luis; Barquero Pérez, Óscar; Mora Jimenez, I; Goya Esteban, R; Gimeno Blanes, J; García Alberola, A
Though alternans phenomena in the cardiac repolarization phase has been shown to be related to arrhythmgenesis, a definitive estimation method from the T wave of ECG recordings is not yet available. We propose a statistical signal processing scheme which compares the T-wave morphology of even and odd beats by using a running matched filter, in order to increase the signal to noise ratio of the estimation. Given that previously proposed hypothesis tests for alternans detection rely on the knowledge of noise statistical distribution, we also analyzed the usefulness of a nonparametric bootstrap test. Data set composed of 100 ECG recordings included in the Challenge Database were used. Principal Component Analysis was previously made for multilead recordings. Subsequent preprocessing for each available lead consisted of conventional baseline removing, filtering, R-wave detection, exclusion of too noisy segments, T-wave segmentation, and template generation for even and odd beats. The difference between the template and a given beat was obtained by minimizing the absolute error of their comparison with a windowed circular shift. A paired bootstrap resampling test was made for deciding whether the averaged differences between the template and the T-waves were significant compared to the noise level.
Nonparametric Model Comparison and Uncertainty Evaluation for Signal Strength Indoor Location.
(2009-06-15T10:23:01Z) Figuera Pozuelo, Carlos; Mora Jimenez, I; Guerrero Curieses, A; Rojo-Álvarez, José Luis; Everss, E; Wilby, M; Ramos López, J
Indoor Location (IL) using Received Signal Strength (RSS) is receiving much attention, mainly due to its ease of use in deployed IEEE 802.11b (WiFi) wireless networks. Fingerprinting is the most widely used technique. It consists of estimating position by comparison of a set of RSS measurements, made by the mobile device, with a database of RSS measurements whose locations are known. However, the most convenient data structure to be used, and the actual performance of the proposed fingerprinting algorithms, are still controversial. In addition the statistical distribution of indoor RSS is not easy to characterize. Therefore, we propose here the use of nonparametric statistical procedures for diagnosis of the fingerprinting model, specifically: (1) A non parametric statistical test, based on paired bootstrap resampling, for comparison of different fingerprinting models; (2) New accuracy measurements (the uncertainty area and its bias) which take into account the complex nature of the fingerprinting output. The bootstrap comparison test and the accuracy measurements are used for RSS-IL in ourWiFi network, showing relevant information relating to the different fingerprinting schemes that can be used.