Stefanie Heinke

Modeling and simulation of the cardiovascular system: a review of applications, methods, and potentials / Modellierung und Simulation des Herz-Kreislauf-Systems: ein Überblick zu Anwendungen, Methoden und Perspektiven

Abstract Proper function of the cardiovascular system is indispensible to human survival. However, this system is dominated by complex interactions between different physiological processes and control mechanisms. A structured analysis and a mathematical description of this system can provide more insight, and a computer-based simulation of dynamic processes in the cardiovascular system could be applied in numerous tasks. This article gives a review of different approaches to cardio-circulatory modeling and discusses methodological aspects and fields of application for several classes of models. Zusammenfassung Die Funktion des Herz-Kreislauf-Systems ist eine wichtige Voraussetzung für das Überleben des Menschen. Dieses System ist jedoch bestimmt von komplexen Wechselwirkungen zwischen verschiedensten physiologischen Prozessen und Regelungsmechanismen. Eine strukturierte mathematische Beschreibung und ein dynamisches Simulationsmodell können helfen, das Herz-Kreislauf-System besser zu verstehen. Dieser Artikel bietet einen Überblick zu verschiedenen Ansätzen in der kardiovaskulären Modellbildung und vergleicht methodische Aspekte und Anwendungsgebiete der einzelnen Modellarten.

Modeling a healthy and a person with heart failure conditions using the object-oriented modeling environment Dymola

Several mathematical models of different physiological systems are spread through literature. They serve as tools which improve the understanding of (patho-) physiological processes, may help to meet clinical decisions and can even enhance medical therapies. These models are typically implemented in a signal-flow-oriented simulation environment and focus on the behavior of one specific subsystem. Neglecting other physiological subsystems and using a technical description of the physiology hinders the exchange with and acceptance of clinicians. By contrast, this paper presents a new model implemented in a physical, object-oriented modeling environment which includes the cardiovascular, respiratory and thermoregulatory system. Simulation results for a healthy subject at rest and at the onset of exercise are given, showing the validity of the model. Finally, simulation results showing the interaction of the cardiovascular system with a ventricular assist device in case of heart failure are presented showing the flexibility and mightiness of the model and the simulation environment. Thus, we present a new model including three important physiological systems and one medical device implemented in an innovative simulation environment.

Methods of design, simulation, and control for the development of new VAD/TAH concepts / Methoden zur Konstruktion, Simulation und Regelung für die Entwicklung von neuen VAD/TAH-Konzepten

Abstract Cardiovascular diseases are a major cause of death worldwide. If medical treatments fail to restore adequate blood flow in a patient, mechanical support is needed. To date, many different types of blood pumps have been developed, but only few are clinically available. This review article describes the challenges involved in this field of research and gives an overview of the development process. Past developments as well as current and new technologies and approaches applied are summarized. Finally, a perspective for improved devices is discussed. Zusammenfassung Herz-Kreislauf-Erkrankungen sind die häufigste Todesursache weltweit. Wenn eine hinreichende Durchblutung mit konventionellen Therapien nicht gewährleistet werden kann, ist eine mechanische Kreislaufunterstützung notwendig. In der Vergangenheit wurde eine Vielzahl von Blutpumpen entwickelt, von denen sich jedoch nur wenige klinisch etabliert haben. Dieser Artikel beschreibt die Herausforderungen bei ihrer Konstruktion und gibt eine Übersicht über den Entwicklungsprozess. Bisherige Entwicklungen, aktuelle und zukünftige Technologien und Lösungsansätze werden zusammenfassend dargestellt. Abschließend werden Verbesserungspotentiale bei der Blutpumpenentwicklung diskutiert.

Control strategies for mechanical heart assist systems

Mechanical Heart Assist Systems are one option to treat cardiovascular disease being the main cause of death worldwide. Since the reliability of these devices has increased and patients on mechanical heart assist systems are even able to leave the hospital, the need for enhanced control algorithms that automatically adapt the output of the devices to the patients need is growing. This review paper aims to give an overview on control strategies proposed for Mechanical Heart Assist Systems. Typical aspects of designing control algorithms are introduced and issues regarding the control of biomedical applications are discussed. Different approaches to control Mechanical Heart Assist Systems are presented and research topics that need further development are identified.

Modellierung und Regelung eines hydraulischen HIL-Simulators zum Test von Herzunterstützungssystemen / Modeling and Control of a Hydraulic Simulator for Ventricular Assist Device Testing

Zusammenfassung In diesem Beitrag werden ein Modell und ein Regelkonzept für einen Hardware-in-the-Loop (HIL)- Prüfstand zum Testen von Herzunterstützungssystemen vorgestellt. Dieser HIL-Prüfstand simuliert die ein -und auslassseitigen Zustandsgrößen, denen ein Herzunterstützungssystem im Körper ausgesetzt ist, so dass damit schnell und kostengünstig Regelungen von Herzunterstützungssystemen unter hochdynamischen Bedingungen getestet werden können. Die Modellierung des HIL-Prüfstands erfolgt mit den Lagrangeschen Gleichungen 2. Art. Als Regelungsverfahren werden ein LQRRegler und ein PI-Regler in dem Mehrgrößensystem eingesetzt. Zur Evaluation der Regelung werden ventrikuläre und arterielle Drücke aus einer Softwaresimulation des Herzkreislaufsystems auf den HIL-Prüfstand übertragen und erfolgreich nachgebildet. Summary In this paper, a modeling approach and a control concept for a Hardware-in-the-Loop (HIL) test bench for ventricular assist devices are presented. The purpose of the HIL test bench is to simulate the pressures at the in- and outport of a ventricular assist device as given by the cardiovascular system of a patient. This enables testing of control algorithms for ventricular assist devices in an efficient and cost-saving manner. The modeling is performed using Lagrange’s equations. The control concept is based on PI- and LQR-control. The control concept is evaluated by transferring ventricular and arterial pressures generated by a simulation of the cardiovascular system to the HIL test bench.

Respiratory Mechanics, Gas Transport and Perfusion During Exercise

Abstract Several mathematical models of the respiratory system and gas transport have been proposed in order to explain the behavior of this complex system. These potential tools can help clinicians to understand pathophysiological processes as well as to improve medical therapies, especially under the clinical point of view. In this paper, a nonlinear dynamic mathematical model able to represent the relationship between lungs, blood and tissues is proposed. The aim of this system is to analyse the mechanics of breathing, gas transport and perfusion under different circumstances: resting, exercise and recovery. In this paper four principal components of this physiological system are highly focused: lungs, pulmonary capillaries, lungs and systemic capillaries. For the implementation, Dymola, an objected-oriented physical modelling language, was used. The results achieved show the ability of the implemented model to reproduce the main features of the systems response in terms of ventilation and gas exchange. Moreover, it also demonstrates the ability and feasibility to simulate the dynamics of pressures and concentrations of carbon dioxide (CO 2 ) and oxygen (O 2 ) in the pulmonary and systemic circulation. In order to validate the results, they are compared with data from other papers. To sum up, by implementing this sophisticated model the multifactorial interactions between changes in ventilation, perfusion and diffusion before, during and after exercise can be studied.

Dynamic Hardware-in-the-Loop Test Stand for Total Artificial Hearts

Abstract A new tool for the development process of total artificial hearts (TAH) dedicated for the long-term use is presented. The focus is on the modelling of a dynamic Mock Circulatory Loop, which can adapt to different physiological conditions and simulates a natural transient behaviour in between. This is important for the development of adaptive control algorithms which are able to respond to the physiological demand. After an introduction of the clinical problem, the Mock Circulatory Loop is described. The concept for the simulation process of the TAH with the Mock Circulatory Loop and with the hardware to realize Hardware-in-the-Loop (HIL) simulation is introduced. Finally, some results of the first measurements with a component of the Mock Circulatory Loop are presented.