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  • 1
    Electronic Resource
    Electronic Resource
    Robust Nonlinear Autoregressive Moving Average Model Parameter Estimation Using Stochastic Recurrent Artificial Neural Networks (1999)
    Springer
    Annals of biomedical engineering 27 (1999), S. 538-547 
    Details
    ISSN: 1573-9686
    Keywords: ARMA ; NARMA ; Polynomial function ; Backpropagation ; Measurement noise ; Dynamic noise ; Deterministic ; Stochastic ; Recurrent neural network
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract In this study, we introduce a new approach for estimating linear and nonlinear stochastic autoregressive moving average (ARMA) model parameters, given a corrupt signal, using artificial recurrent neural networks. This new approach is a two-step approach in which the parameters of the deterministic part of the stochastic ARMA model are first estimated via a three-layer artificial neural network (deterministic estimation step) and then reestimated using the prediction error as one of the inputs to the artificial neural networks in an iterative algorithm (stochastic estimation step). The prediction error is obtained by subtracting the corrupt signal of the estimated ARMA model obtained via the deterministic estimation step from the system output response. We present computer simulation examples to show the efficacy of the proposed stochastic recurrent neural network approach in obtaining accurate model predictions. Furthermore, we compare the performance of the new approach to that of the deterministic recurrent neural network approach. Using this simple two-step procedure, we obtain more robust model predictions than with the deterministic recurrent neural network approach despite the presence of significant amounts of either dynamic or measurement noise in the output signal. The comparison between the deterministic and stochastic recurrent neural network approaches is furthered by applying both approaches to experimentally obtained renal blood pressure and flow signals. © 1999 Biomedical Engineering Society. PAC99: 8710+e, 8719Uv, 0705Mh
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1114/1.197
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    Paper (German National Licenses)
    Fulltext
  • 2
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    Spatio-temporal oscillations of individual mitochondria in cardiac myocytes reveal modulation of synchronized mitochondrial clusters (2010)
    National Academy of Sciences
    Details
    Publication Date: 2010-07-23
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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    PAPER CURRENT
  • 3
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    Images in cardiovascular medicine. T-wave alternans preceding torsade de pointes ventricular tachycardia (2000)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: No abstract available
    Keywords: Life Sciences (General)
    Type: Circulation (ISSN 0009-7322); Volume 101; 21; 2550
    Format: text
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    NASA TECHNICAL REPORTS
  • 4
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    T-wave alternans and dispersion of the QT interval as risk stratification markers in patients susceptible to sustained ventricular arrhythmias (1998)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: T-wave alternans and QT dispersion were compared as predictors of the outcome of electrophysiologic study and arrhythmia-free survival in patients undergoing electrophysiologic evaluation. T-wave alternans was a highly significant predictor of these 2 outcome variables, whereas QT dispersion was not.
    Keywords: Life Sciences (General)
    Type: The American journal of cardiology (ISSN 0002-9149); Volume 82; 9; 1127-9, A9
    Format: text
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  • 5
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    Clinical utility of T-wave alternans (1997)
    In:  Other Sources
    Details
    Publication Date: 2019-08-16
    Description: Electrical alternans represents a variation in the morphology of electrocardiographic complexes on an every-other-beat basis in an ABABAB... pattern. Apparent electrical alternans associated with pericardial effusion results from rotation of the heart in the pericardial sac, and not true alternation in electrical conduction patterns. In contrast, true electrical alternans results from an alternation in electrical conduction patterns in the heart itself. Repolarization alternans is true electrical alternans associated with the ST segment and T wave of the electrocardiogram (ECG). Here we will focus on T-wave alternans (TWA) and its association with susceptibility to ventricular tachyarrhythmias. Electrical alternans was reported in the literature as early as 1909. Historically, electrical alternans has been regarded as a fairly rare electrocardiographic abnormality. Case reports of electrical alternans have been associated with a variety of disease states, including acute ischemia, Prinzmetal's angina, a variety of electrolyte abnormalities, and the long QT syndrome. Interestingly, patients born with the prolonged QT syndrome have a very high incidence of sudden cardiac death at an early age. Schwartz and Malliani showed that patients with the prolonged QT syndrome who do not demonstrate alternans at rest, may evidence alternans during stress such as emotional excitement. Thus, over the years electrical alternans has been associated anecdotally with conditions associated with an increased risk of ventricular arrhythmias. In 1948, Kalter reviewed the world literature on electrical alternans and found a total of 41 reported cases. In addition, he reviewed clinical ectrocardiograms from 6059 patients and found five new cases (incidence of less than 1 in 1000 patients). Interestingly, he found a very high mortality, 62%, associated with this condition. Despite the clinical associations reported in the literature, the consensus view of electrical alternans until recent years has been that alternans is an electrocardiographic curiosity rarely encountered in clinical practice which, when identified, does not have specific clinical significance.
    Keywords: Life Sciences (General)
    Type: Cardiac electrophysiology review (ISSN 1385-2264); 1; 3; 390-4
    Format: text
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  • 6
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    Applicability of the single equivalent point dipole model to represent a spatially distributed bio-electrical source (2001)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Although the single equivalent point dipole model has been used to represent well-localised bio-electrical sources, in realistic situations the source is distributed. Consequently, position estimates of point dipoles determined by inverse algorithms suffer from systematic error due to the non-exact applicability of the inverse model. In realistic situations, this systematic error cannot be avoided, a limitation that is independent of the complexity of the torso model used. This study quantitatively investigates the intrinsic limitations in the assignment of a location to the equivalent dipole due to distributed electrical source. To simulate arrhythmic activity in the heart, a model of a wave of depolarisation spreading from a focal source over the surface of a spherical shell is used. The activity is represented by a sequence of concentric belt sources (obtained by slicing the shell with a sequence of parallel plane pairs), with constant dipole moment per unit length (circumferentially) directed parallel to the propagation direction. The distributed source is represented by N dipoles at equal arc lengths along the belt. The sum of the dipole potentials is calculated at predefined electrode locations. The inverse problem involves finding a single equivalent point dipole that best reproduces the electrode potentials due to the distributed source. The inverse problem is implemented by minimising the chi2 per degree of freedom. It is found that the trajectory traced by the equivalent dipole is sensitive to the location of the spherical shell relative to the fixed electrodes. It is shown that this trajectory does not coincide with the sequence of geometrical centres of the consecutive belt sources. For distributed sources within a bounded spherical medium, displaced from the sphere's centre by 40% of the sphere's radius, it is found that the error in the equivalent dipole location varies from 3 to 20% for sources with size between 5 and 50% of the sphere's radius. Finally, a method is devised to obtain the size of the distributed source during the cardiac cycle.
    Keywords: Life Sciences (General)
    Type: Medical & biological engineering & computing (ISSN 0140-0118); 39; 5; 562-70
    Format: text
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  • 7
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    Linear and nonlinear system identification of autonomic heart-rate modulation (1997)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: No abstract available
    Keywords: Life Sciences (General)
    Type: IEEE engineering in medicine and biology magazine : the quarterly magazine of the Engineering in Medicine & Biology Society (ISSN 0739-5175); 16; 5; 96-105
    Format: text
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  • 8
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    Prognostic significance of electrical alternans versus signal averaged electrocardiography in predicting the outcome of electrophysiological testing and arrhythmia-free survival (1998)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: OBJECTIVE: To investigate the accuracy of signal averaged electrocardiography (SAECG) and measurement of microvolt level T wave alternans as predictors of susceptibility to ventricular arrhythmias. DESIGN: Analysis of new data from a previously published prospective investigation. SETTING: Electrophysiology laboratory of a major referral hospital. PATIENTS AND INTERVENTIONS: 43 patients, not on class I or class III antiarrhythmic drug treatment, undergoing invasive electrophysiological testing had SAECG and T wave alternans measurements. The SAECG was considered positive in the presence of one (SAECG-I) or two (SAECG-II) of three standard criteria. T wave alternans was considered positive if the alternans ratio exceeded 3.0. MAIN OUTCOME MEASURES: Inducibility of sustained ventricular tachycardia or fibrillation during electrophysiological testing, and 20 month arrhythmia-free survival. RESULTS: The accuracy of T wave alternans in predicting the outcome of electrophysiological testing was 84% (p 〈 0.0001). Neither SAECG-I (accuracy 60%; p 〈 0.29) nor SAECG-II (accuracy 71%; p 〈 0.10) was a statistically significant predictor of electrophysiological testing. SAECG, T wave alternans, electrophysiological testing, and follow up data were available in 36 patients while not on class I or III antiarrhythmic agents. The accuracy of T wave alternans in predicting the outcome of arrhythmia-free survival was 86% (p 〈 0.030). Neither SAECG-I (accuracy 65%; p 〈 0.21) nor SAECG-II (accuracy 71%; p 〈 0.48) was a statistically significant predictor of arrhythmia-free survival. CONCLUSIONS: T wave alternans was a highly significant predictor of the outcome of electrophysiological testing and arrhythmia-free survival, while SAECG was not a statistically significant predictor. Although these results need to be confirmed in prospective clinical studies, they suggest that T wave alternans may serve as a non-invasive probe for screening high risk populations for malignant ventricular arrhythmias.
    Keywords: Life Sciences (General)
    Type: Heart (British Cardiac Society) (ISSN 1355-6037); 80; 3; 251-6
    Format: text
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