A. Urbaszek

A heart and circulation model with emphasis on short-term regulation

A computer model of human heart and circulation will be presented, which was designed to support the development of rate-adaptive pacemakers. The goal is to describe short-term regulatory processes of the cardiovascular system, especially in the heart itself, under both normal and pathological conditions.

A mathematical approach to short-term baroreceptor behaviour

A mathematical model of short-term baroreceptor behaviour will be presented, which is determined for operation within a computer simulation of the cardiovascular system [4]. It describes the time-dependent relationship between instantaneous blood pressure and evoked impulse frequency in an unifying concept including the most important static and dynamic features like sigmoidal curve shape, differential pressure increment and asymmetry of response.

Simulation of closed-loop rate-adaptive pacing with a numerical heart and circulation model

A numerical model of the human cardiovascular system was developed to study the chronotropic and inotropic responses of the heart as well as peripheral adaptation to changing metabolic demands. Autonomic nervous system (ANS) control covers all three levels of the model: circulation, heart mechanics and myocardial cell. The purpose of the simulations is to investigate the control aspects of rate responsive pacing and to develop and test algorithms for rate adaptation based on cardiac control signals, of which unipolar intracardiac impedance measurements are of special interest.<<ETX>>

Herz/Kreislaufmodell zur Simulation chronotroper und inotroper Regulationsvorgänge

Kurzfassung — Das vorgestellte Modell des menschlichen kardiovaskulären Systems dient der Simulation von kurzzeitigen Regulationsvorgängen zur Anpassung der Herzfunktion an unterschiedliche Kreislaufbedürfnisse. Der Schwerpunkt liegt dabei auf den chronotropen und inotropen Wirkungen des autonomen Nervensystems (ANS) auf den Kontraktionsvorgang. Damit eignet sich das Modell als Hilfsmittel beim Entwurf und der Erprobung frequenzadaptiver Schrittmacher, da auch pathologische Veränderungen simuliert werden können.

Kontinuierliche Impedanzmessung mit synchronisierter Ultraschallaufzeichnung zur Untersuchung der Belastungs- und Frequenzabhängigkeit des intrakardialen Impedanzsignals

Einleitung: In diesem Beitrag wird ein klinischer Versuch zur Validierung des Konzepts der Belastungsdetektion mittels intrakardialer Impedanzmessung [2,3] vorgestellt. Dabei sollen im Rahmen einer kontinuierlichen, d.h. den vollständigen Herzzyklus umfassenden Messung der intrakardialen Admittanz weitere Aufschlüsse über den Einfluß von körperlicher Belastung und Stimulationsfrequenz auf das Meßsignal erbracht werden. Neben dem Verhalten während der Austreibungsphase gilt dabei besonderes Augenmerk den Effekten ab der isovolumetrischen Relaxationsphase, in der durch die verminderte Einwirkung von Vorund Nachlast der Durchgriff des autonomen Nervensystems verstärkt zum Tragen kommt [1],

ANS monitoring using right ventricular impedance

Intracardiac impedance measurements allow the monitoring of the contractile status of the heart, which depends mainly on the sympathetic drive by the autonomic nervous system (ANS). The ANS-controlled rate-responsive pacemaker, which uses the stimulating electrode at the same time as the measuring electrode, is of special clinical advantage. The clinical evaluation of this pacing system in more than 200 patients confirmed adequate rate adaptation.<<ETX>>

New concepts in pacemaker technology

Abstrod The aim of today’s pacemaker technology is to maintain a high quality of life and physical perfomace of the patient When natural sinus rhythm i s absent, a series of sensors with complex microelectronic contml circuits meets the need for rate-adaptive pacemaker systems while preserving AV synchrony. But only closed loop control has the potential to restore natural regulation. Intracardiac impedance measurements allow the monitoring of the contractile status of the heart, which depends mainly on the sympathetic drive. The ANS-contmlled pacemaker, which uses the stimulating electrode at the same time as the measuring electrode, is of special cIinical advantage The clinical evaluation of this pacing system in more than 200 patients confirmed adequate rate adaptation. Future developments are likely to make use of this possibility for eg arrhythmia prevention, intensive care monitoring o r as already implemented in conjunction with cardiomyoplasty.

Simulation of the cardiovascular mechanics during rate adaptive pacing

A numerical model of the human cardiovascular system will be presented that was developed for simulating the short-term regulatory processes that adapt the cardiac output of the heart to changing circulatory demands. Both normal and pathological states, e.g. sick sinus or AV block, are considered. The purpose of the simulations is to investigate the control aspects of rate responsive pacing and to develop and test algorithms for rate adaptation based on cardiac control signals.

Simulation des hämodynamischen Verhaltens bei künstlicher frequenzadaptiver Stimulation an einem Herz/Kreislaufmodell

Kurtfassung — Mit Hilfe eines numerischen Modells des menschlichen kardiovaskulären Systems wird das hämodynamischc Verhalten bei künstlicher frequenzadaptiver Stimulation im Vergleich zum Gesunden für verschiedene Belastungssituationen untersucht Im Vordergrund steht die Frage, wie unter speziellen pathologischen Verhältnissen (Sinusknotcnsyndrom, Myokardinsuffizienz) eine optimale Stimulationsfrequenz ermittelt werden kann. Als konkretes Anwendungsheispicl wird der ANSgesteuerte Schrittmacher, der durch unipolare intrakardiale Impedanzmessung einen Kontraktilitätsparameter bestimmt und für die Frequenzadaption nutzt, in das Modell einbezogen.

Evaluation of inotropic state from intracardiac conductance signals using neural networks

A backpropagation network will be presented, which supports the development of rate-adaptive pacemakers by means of evaluation of inotropic state determined from right ventricular intracardiac conductance. Network performance in dependence of data preprocessing is discussed.