ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Biological cybernetics 25 (1977), S. 227-240 
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract An electronic analog that models the burst generating neuronR 15 of theAplysia abdominal ganglion is described. The analog is based on the four branch Hodgkin-Huxley equivalent circuit for a patch of squid axon membrane, with a choice of parameter values appropriate to theAplysia cell membrane. To realize the slow subthreshold oscillations seen in cellR 15 upon exposure to the drug tetrodotoxin (TTX), it was necessary to include two additional conductance branches,g′ Na andg′ K, to the basic Hodgkin-Huxley circuit. Without these, the analog was capable of generating only action potentials and hence termed the “suprathreshold” analog. With all six branches operative, bursts very similar to those seen inR 15 were realized, and subsequent inhibition of the Hodgkin-Huxley sodium conductanceg Na resulted in the desired subthreshold oscillations. The electronic circuitry and the performance of the “suprathreshold” and complete analog are described. An explanation is offered for the progressive widening of the action potentials within a burst seen inR 15. The analog also simulates the phenomenon of potassium ion accumulation outside the cell membrane during a burst, using a local feedback loop to reduce the potassium equilibrium potential in a manner roughly proportional to the logarithm of the time integral of the outward potassium current. Some consequences of this effect are also discussed.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Bulletin of mathematical biology 30 (1968), S. 529-529 
    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Bulletin of mathematical biology 29 (1967), S. 217-226 
    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract The “second method” of Liapunov is used to perform a stability analysis of a mathematical model of the neuron. This analysis is based on the hypothesis that the firing of the neuron coincides with a temporary state of instability of the system, and that the initiation of all-or-none process depends on the magnitude of membrane depolarization and its first time derivative. It is found that the stability (and hence the possibility of a second firing) is restored approximately when the rate of membrane repolarization is at a maximum. This result predicts that the duration of the period of absolute refractoriness in neurons would be about 75 per cent of the spike duration, and thus shorter than the value usually obtained from experimental measurements.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Medical & biological engineering & computing 27 (1989), S. 405-415 
    ISSN: 1741-0444
    Keywords: Cable model ; Cardiac tissue ; Discontinuous propagation ; Electrotonic propagation ; Foot of the action potential
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract This model study describes the electrotonic response of a cable model of cardiac tissue stimulated at one point. The stimulus is applied intracellularly in the form of a 2ms pulse of current of near threshold amplitude. The attenuation of the electrotonic potential with distance and its mode of propagation along the cable are compared for equivalent passive, continuous and discontinuous cables. The three structures have the same basic physical and electrical characteristic and they differ either with respect to being active or passive or to the presence or absence of intercellular gap junctions. In the continuous cable a just subthreshold stimulus produces a local active response which propagates more slowly and is attenuated less rapidly with distance than in a passive cable. The spatial decrement of the local response in a discontinuous cable is faster than in a continuous cable of equal average resistivity. It is suggested that the larger time constant of the foot of the action potential observed in the longitudinal direction in cardiac muscle could be due in part to the electrotonic spread of the local response from the site of stimulation.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Medical & biological engineering & computing 9 (1971), S. 75-75 
    ISSN: 1741-0444
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Medical & biological engineering & computing 13 (1975), S. 370-381 
    ISSN: 1741-0444
    Keywords: E.C.G. ; Arrhythmia ; Computer
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Description / Table of Contents: Sommaire Un nouveau programme d'ordinateur a été mis au point pour extraire les paramètres pertinents de l'électrocardiogramme d'adulte, afin d'interpréter l'arythmie automatique dans le cadre de l'analyse routinière. Aucun programme d'interprétation ne serait acceptable par les cardiologues sans une interprétation de rythme conjuguée à l'interprétation de morphologie, même si, dans une situation de routine, l'interprétation du rythme n'est pas aussi rigoureuse que dans les milieux ambiants du contrôle. Le programme de mesure fonctionne simultanément sur les lignesX, Y etZ du système Frank modifié. Les caractéristiques considérées de l'e.c.g. sont le train d'ondesQRS, les caractéristiques morphologiquesQRS et le train d'ondesP. Bien que le programme fasse toujours l'objet d'une évaluation, plusieurs résultats importants ont été obtenus à partir de l'analyse d'une quantité donnée d'e.c.g. Le mode utilisant la détectionQRS donne une erreur totale de 0,79% par l'addition du nombre de complexesQRS omis et des fausses détections. Le système est apte à réaliser une détection parfaite sur 95% des e.c.g. analysés. La performance sur le classementQRS est de 1,15% des formes d'ondes mal classées, avec un autre taux de 0.67% qui demeure indéfini par suite de la limitation de la capacité de mesure de l'algorithme utilisé; 89·7% des tracés sont complètement exempts d'erreur. L'identification du train d'ondeP est réalisée avec un succès notable. Dans le mode ‘Battement à Battement’, 92·5% des ondesP pour le programme sont présentes dans les tracés pendant la production de 2·2% de phénomènes étrangers.
    Abstract: Zusammenfassung Zum Auszug der entsprechenden Parameter aus den e.k.g.s von Erwachsenen wurde ein neues Rechnerprogramm entwickelt, um automatische Arrhythmien bei der routinemäßigen Untersuchung interpretieren zu können. Ohne Rhythmusinterpretation, die mit der morphologischen Interpretation gekoppelt ist, sollten die Kardiologen keine Interpretations-programme annehmen, selbst wenn die Rhythmusinterpretation bei Routineuntersuchungen nicht so streng ist wie bei der Überwachung. Das Meßprogramm läßt sich gleichzeitig auf denX-,Y- andZ-Abeleitungen des modifizierten Frank-Systems einsetzen. Die berücksichtigten e.k.g.-merkmale sind die WellenserieQRS, die morphologischen WerteQRS und dieP-Wellenserie. Obgleich das Programm noch nicht voll bewertet ist, erhielt man mehrere wichtige Ergebnisse, die auf der Analyse einer bestimmten Anzahl von e.k.g.s beruhen. Bei derQRS-Suche ergibt sich ein Fehler von insgesamt 0·79%, wenn man die Anzahl der ausgelassenenQRS-Komplexe und der falschen Entdeckungen zusammenzählt. Das System kann bei über 95% der analysierten e.k.g.s eine perfekte Entdeckung herbeiführen. Die Leistung bei derQRS-Klassifikation beträgt 1·15% der falsch klassifizierten Wellenformen, mit zusätzlichen 0·67%, die'durch die beschränkte Meßfähigkeit des verwendeten Algorithmus nicht definiert werden. 89·7% der Messungen sind völlig fehlerfrei. Die Identifizierung derP-Wellenserie erreicht man mit weitgehendem Erfolg. Auf der Grundlage von Pulsschlag zu Pulsschlag findet das Programm 92·5% derP-Wellen, während Außeneinwirkungen in Höhe von 2·2% entstehen.
    Notes: Abstract A new computer program has been developed to extract pertinent parameters from the adult e.c.g., for the purpose of automatic arrhythmia interpretation in the context of routine analysis. No interpretation program would be acceptable by cardiologists without a rhythm interpretation coupled to the morphology interpretation even if in routine situations rhythm interpretation is not as stringent as in monitoring environments. The measurements program operates simultaneously on the X, Y and Z leads of the modified Frank system. The e.c.g. features considered are the QRS wavetrain, the QRS morphological characteristics and the P wavetrain. Although the program is still under evaluation, a number of important results have been obtained based on the analysis of a given population of e.c.g.s. The performance on QRS detection gives a total error of 0·79% when adding the number of omitted QRS complexes and false det ections, and the system is able to realise perfect detection on over 95% of the e.c.g.s analysed. The performance on QRS classification is 1·85% of misclassified waveforms, with a further 0·67% which remains undefined due to the limitation in measurement capability of the algorithm used; 89·7% of the tracings are completely error free. The identification of the P wavetrain is achieved with a good degree of success. On a beat-to-beat basis, the program finds 92·5% of the P waves present in the tracings while generating 2·2% extraneous events. However, only 53% of the tracings are error free.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Medical & biological engineering & computing 4 (1966), S. 357-366 
    ISSN: 1741-0444
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Description / Table of Contents: Sommaire Un modèle en boucle du neurone est décrit, basé sur une représentation à deux lieus du motoneurone de la moëlle épinière du chat. Cette analogie est équivalente au modèle de membrane deHodgkin etHuxley dans lequel tous les composants du courant d'action ont été réunis. En utilisant la technique de la “deuxième méthode” de Liapunov, on effectue une analyse de la stabilité qui fournit des résultats concernant l'utilisation du potentiel d'action et de sa dérivée première pour représenter les cellules nerveuses. On donne enfin un exemple dans lequel le modèle est utilisé pour étudier un réseau de neurones comprenant dans la boucle de réaction négative une cellule de Renshaw.
    Abstract: Zusammenfassung Ein Feedbackmodell des Neurons wird beschrieben, das auf der doppelörtigen Repräsentierung der Rückenmarksneurone der Katze beruht. Dieses Analogon ist dem Membranmodell von Hodgkin und Huxley äquivalent, das alle Komponenten des Aktionsstroms enthält. Unter Verwendung des Verfahrens der “zweiten Methode” nach Liapunow wird eine Stabilitätsanalyse unternommen, die Ergebnisse bezüglich der Brauchbarkeit des Aktionspotentials und seiner ersten Ableitung nach der Zeit für die Charakterisierung von Nervenzellen liefert. Schließlich wird ein Beispiel der Anwendung des Modells gegeben, in dem ein Neuronennetzwerk untersucht wird, das den negativen Feedback von Renshawzellen betrifft.
    Notes: Abstract A feedback model of the neuron is described, based on a double-locus representation of the cat spinal cord motoneuron. This analog is equivalent to the Hodgkin and Huxley membrane model in which all the components of the action current have been lumped. By using the technique of the “second method” of Liapunov a stability analysis is made which yields results pertaining to the use of the action potential and its first time derivative for the characterization of nerve cells. Finally an exmple is given in which the model is used to investigate a neuronal network involving Renshaw cell negative feedback.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Medical & biological engineering & computing 9 (1971), S. 13-21 
    ISSN: 1741-0444
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Description / Table of Contents: Sommaire Ce mémoire décrit un modèle électronique du système de conduction du coeur, sous la forme d'une unité de simulation pour les arythmies cardiaques. Les suppositions de base faites sont l'existence de deux centres cardiaques distincts pour le règlement de l'allure cardiaque et la possibilite d'une interaction réciproque entre eux. Des détails concernant la construction de l'unité de simulation sont donnés et son opération est illustrée avec l'aide de quelques exemples simples d'arythmies cardiaques. Les avantages présentés par cet appareil pour l'instruction et la démonstration des types d'arythmie cardiaque variés, sont aussi soulignés.
    Abstract: Zusammenfassung In dieser Abhandlung wird ein elektronisches Modell des Kardia-Leitsystems beschrieben. Es beruht auf der grundsätzlichen Annahme der Existenz zweier, verschiedener Keith-Flackscher Knotenzentren und der Möglichkeit einer gegenseitigen Wechselaktion zwischen denselben. Es werden Konstruktionseinzelheiten des Simulierapparates angegeben und seine Leistungsfähigkeit durch vereinzelte Beispiele von Herzarrhythmie illustriert. Die Vorteile dieser Vorrichtung für den Unterricht und die Vorführung verschiedener kardiakarrhythmischer Beispiele werden hervorgehoben.
    Notes: Abstract This paper describes an electronic model of the conduction system of the heart, in the form of a simulation unit for cardiac arrhythmias. The basic assumptions made are the existence of two distinct cardiac pacemaking centres, and the possibility of reciprocal interaction between them. Details concerning the construction of the simulation unit are given, and its operation is illustrated by means of a few simple examples of cardiac arrhythmias. The advantages presented by this device for teaching and demonstration of various cardiac arrhythmic patterns are also emphasized.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Annals of biomedical engineering 18 (1990), S. 1-17 
    ISSN: 1573-9686
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract We describe an alternative formulation of the cable equation to model excitation in a cylinder of cardiac fiber. The formulation uses Green's theorem to develop equations for the extracellular and intracellular potential on either side of the excitable membrane, the dynamics of which are described by a Hodgkin-Huxley type model, without assuming that the radial current is zero. These equations are discretized to yield a system of linear equations which are solved at each instant in time. We found no qualitative differences between this approach and the standard cable model for parameters within accepted physiological limits. When the cable diameter is of the same order as the length constant the new formulation takes into account the intracellular potential change in the radial direction and gives an accurate expression of the conduction velocity.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Annals of biomedical engineering 22 (1994), S. 568-591 
    ISSN: 1573-9686
    Keywords: Ionic model ; Propagation ; Triggered secondary repolarization ; Wavelength ; Excitable gap ; Triggered excitability recovery
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract This paper describes the dynamics of circus movement around a fixed obstacle, using a one-dimensional continuous and uniform ring model of cardiac tissue to simulate sustained reentry. The membrane ionic current is simulated by a modified Beeler-Reuter formulation in which the kinetics of the fast sodium current were updated using more recent voltageclamp data. Changes in the ring length are used to modify the dynamics of reentry. Reentry is stable if the ring length (X) exceeds a critical value (X crit) and complete block occurs ifX is below a minimum (X min). Irregular sustained reentry is observed at intermediate ring lengths, as a narrow range of aperiodic reentry nearX crit, and a larger range of quasi-periodic reentry at shorter ring lengths. The basic pattern of irregular reentry is an alternation between long and short cycle length, action potential duration (APD), diastolic interval (DIA), wavelength, and excitable gap. In aperiodic reentry cycle length variations are small,APD andDIA fluctuations are of medium amplitude, and conduction velocity over the whole pathway is essentially constant during successive turns. Much larger fluctuations in these various quantities occur during quasi-periodic reentry, and they increase in size asX approachesX min. The complexity of quasiperiodic reentry patterns is related to three factors: the slope of theAPD versus DIA relation, which is greater than 1, the existence of a zone of slow conduction on the ring when the excitable gap becomes quite short, and the occurrence of triggered waves of secondary repolarization and excitability recovery. In the present model, quasi-periodic reentry with triggered secondary recovery covers most of the range of ring lengths, giving rise to sustained irregular reentry. There is very close agreement between our simulation results and experimental data obtained on rings of cardiac tissue.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...