Bernhard P. Lampe

Physiological control of a rotary blood pump with selectable therapeutic options: control of pulsatility gradient.

A control strategy for rotary blood pumps meeting different user-selectable control objectives is proposed: maximum support with the highest feasible flow rate versus medium support with maximum ventricular washout and controlled opening of the aortic valve (AoV). A pulsatility index (PI) is calculated from the pressure difference, which is deduced from the axial thrust measured by the magnetic bearing of the pump. The gradient of PI with respect to pump speed (GPI) is estimated via online system identification. The outer loop of a cascaded controller regulates GPI to a reference value satisfying the selected control objective. The inner loop controls the PI to a reference value set by the outer loop. Adverse pumping states such as suction and regurgitation can be detected on the basis of the GPI estimates and corrected by the controller. A lumped-parameter computer model of the assisted circulation was used to simulate variations of ventricular contractility, pulmonary venous pressure, and aortic pressure. The performance of the outer control loop was demonstrated by transitions between the two control modes. Fast reaction of the inner loop was tested by stepwise reduction of venous return. For maximum support, a low PI was maintained without inducing ventricular collapse. For maximum washout, the pump worked at a high PI in the transition region between the opening and the permanently closed AoV. The cascaded control of GPI and PI is able to meet different control objectives and is worth testing in vitro and in vivo.

Application of Laplace transformation for digital redesign of continuous control systems

A frequency method of optimal digital re-design of an existing continuous-time system by a quadratic criterion is presented. The method is based on the use of Laplace transformation in continuous time and a parametrization of the set of admissible controllers. The proposed technique makes it possible to solve the optimization problem directly by employing input-output relations without an auxiliary passage to the state space. With such an approach the synthesis procedure is often greatly simplified. The method has the important feature that pure delays in the digital redesigned system can be taken into account in a simple way. It is shown that the presented method can be generalized onto different LQ-optimization problems for sampled-data systems.

Stability investigation for linear periodic time-delayed systems using Fredholm theory

A single-loop linear periodic system with time delay is considered. Using the mathematical tool of integral Fredholm equations of the second kind, a characteristic function is constructed, the roots of which are inverses of the multipliers of the system. Rigorous sufficient stability conditions are given, which are based on approximate representation of the characteristic function in the form of a polynomial.

Frequency-domain method for H 2 optimization of time-delayed sampled-data systems

Abstract A frequency domain method based on the parametric transfer function concept is developed for the design of digital control systems with time-delayed continuous-time plants. The method allows to investigate the behavior of sampled-data systems in continuous-time in terms of input-output relations. An algorithm is presented for the design of an optimal digital controller that minimizes a quadratic cost functional under stochastic disturbances. The method is applicable to the design of digital controllers for arbitrary linear continuous-time plants.

The benefits of using Guyton's model in a hypotensive control system

In order to improve the intraoperative applications, this paper presents the advantages of using Guytons model in hypotensive control system development. In this system, the mean arterial pressure is decreased and maintained at a low level during anaesthesia by controlling sodium nitroprusside infusion rate. The key of the study is to develop a physiological model of cardiovascular dynamics to present the mean arterial pressure response to sodium nitroprusside, which was considered as a linear model in most of known blood pressure control systems. Being linear, the previous models cannot accurately mimic a physiological system of human circulation, especially at deep hypotensive control with strong reaction of the body. The enhanced model in this study was modified based on Guytons model of human circulation. It is useful to design a PID controller, which allows studying and handling the wide range of the body sensitivities. This model is also helpful for studying the behaviors of patients under anaesthesia conditions, such as the perfusion of organs and the reaction of the body at hypotensive state. A fuzzy gain scheduler and a supervising algorithm were also developed for online tuning the controller to handle the behavior of the body. The control system was tested on 25 experiments on seven pigs in the animal laboratory. Simulation and experiment results proved the usefulness of Guytons model in control system design which can present the dynamical response of blood pressure in the circulation under and after hypotensive control. The results also indicated the safety and stability of the controller.

A DEVS-based approach for modeling and simulation of hybrid variable structure systems

The modular-hierarchical modeling subdivides a system into dynamic describing atomic, and structure describing coupled systems. Due to the usally static structure of coupled systems, it can sometimes be hard to realize a component-oriented mapping of real system elements in model components. Hence, several approaches to model structural changes are developed, which are roughly classified in the paper.

Entwurf optimaler digitaler Kursregler mit Hilfe von Parametrischen Übertragungsfunktionen

Prof. Dr. rer. nat. Dr.-Ing. Yephim N. Rosenwasser ist Professor für Regelungstechnik und Leiter des Lehrstuhls für Automat is ierung von Schiffsanlagen an der Meerestechnischen Universität Sankt Petersburg, Rußland. Hauptarbeitsgebiete: Regelungstheorie, zeitvariante und nichtlineare Mehrgrößensysteme. Adresse: Meerestechnische Universität Sankt Petersburg, Lehrstuhl Automatis ierung von Schiffsanlagen, 190008 Sankt Petersburg, Rußland

Fully autonomous preload-sensitive control of implantable rotary blood pumps.

A pulsatility-based control algorithm with a self-adapting pulsatility reference value is proposed for an implantable rotary blood pump and is to be tested in computer simulations. The only input signal is the pressure difference across the pump, which is deduced from measurements of the pumps magnetic bearing. A pulsatility index (PI) is calculated as the mean absolute deviation from the mean pressure difference. As a second characteristic, the gradient of the PI with respect to the pump speed is derived. This pulsatility gradient (GPI) is used as the controlled variable to adjust the operating point of the pump when physiological variables such as the systemic arterial pressure, left ventricular contractility, or heart rate change. Depending on the selected mode of operation, the controller is either a linear controller or an extremum-seeking controller. A supervisory mechanism monitors the state of the system and projects the system into the region of convergence when necessary. The controller of the GPI continuously adjusts the reference value for PI. An underlying robust linear controller regulates the PI to the reference value in order to take into account changes in pulmonary venous return. As a means of reacting to sudden changes in the venous return, a suction detection mechanism was included. The control system is robustly stable within a wide range of physiological variables. All the clinician needs to do is to select between the two operating modes. No other adjustments are required. The algorithm showed promising results which encourage further testing in vitro and in vivo.

Design and implementation of a control system reflecting the level of analgesia during general anesthesia.

Abstract Introduction: Measuring and ensuring an adequate level of analgesia in patients are of increasing interest in the area of automated drug delivery during general anesthesia. Therefore, the aim of this investigation was to develop a control system that may reflect the intraoperative analgesia value. Our hypothesis was that a feedback controller could be applied in clinical practice safely and at an adequate quality of analgesia. The purpose of this study was to evaluate the practical feasibility of such a system in a clinical setting. Methods: The control system for the level of analgesia described in this paper relies on a parameter combination of heart rate variability (HRV), heart rate (HR), and blood pressure (mean arterial pressure, MAP), which serve as input variables for an expert system. For this fuzzy system, the experience of the participating anesthesiologists was translated into a set of fuzzy rules. In a pilot trial, the control system for automated titration of remifentanil, a short-acting opioid, was tested combined with a closed-loop propofol infusion system for hypnosis. Ten adult patients (4 women, 6 men), aged 22–52 years (median, 45 years; range, 29–49 years), with an American Society of Anesthesiologists physical status class I or II and who were scheduled for elective trauma surgery in a supine position were enrolled in this prospective trial. The precision of the system was calculated using internationally defined performance parameters. Results: There was no human intervention necessary during the computer-controlled administration of propofol and remifentanil, and operating conditions were satisfactory in all patients. All patients assessed the quality of anesthesia as “good” to “very good”. Median performance error, median absolute performance error, and wobble for HR and MAP during maintenance of anesthesia were -8.98 (5.32), 10.08 (4.17), and 2.68 (1.29) and -4.51 (12.73), 13.63 (2.27), and 3.90 (2.08) [mean (SD)], respectively. Conclusion: The control system, reflecting the level of analgesia during general anesthesia designed and evaluated in this study, allows for a clinically practical, nearly fully automated infusion of an opioid during medium-length surgical procedures with acceptable technical requirements and an adequate precision.

Statistical analysis of stable FDLCP systems by parametric transfer matrices

This paper considers the problem of determining the statistical characteristics of the response of internally stable finite-dimensional continuous-time periodic (FDLCP) systems to stationary stochastic input signals. Closed formulae for calculating the variance matrix of the state and the output vectors are derived, as well as for the mean variance of the output and the 2-norm of the systems, where only matrices of finite dimension are used. The method bases on application of the parametric transfer matrix (PTM) and needs a precalculation of the transition matrix of the system on the interval 0≤  t ≤ T, where T is the period of the system.