Christian Brendle

Evaluation of a 433 MHz Band Body Sensor Network for Biomedical Applications

Body sensor networks (BSN) are an important research topic due to various advantages over conventional measurement equipment. One main advantage is the feasibility to deploy a BSN system for 24/7 health monitoring applications. The requirements for such an application are miniaturization of the network nodes and the use of wireless data transmission technologies to ensure wearability and ease of use. Therefore, the reliability of such a system depends on the quality of the wireless data transmission. At present, most BSNs use ZigBee or other IEEE 802.15.4 based transmission technologies. Here, we evaluated the performance of a wireless transmission system of a novel BSN for biomedical applications in the 433 MHz ISM band, called Integrated Posture and Activity NEtwork by Medit Aachen (IPANEMA) BSN. The 433 MHz ISM band is used mostly by implanted sensors and thus allows easy integration of such into the BSN. Multiple measurement scenarios have been assessed, including varying antenna orientations, transmission distances and the number of network participants. The mean packet loss rate (PLR) was 0.63% for a single slave, which is comparable to IEEE 802.15.4 BSNs in the proximity of Bluetooth or WiFi networks. Secondly, an enhanced version is evaluated during on-body measurements with five slaves. The mean PLR results show a comparable good performance for measurements on a treadmill (2.5%), an outdoor track (3.4%) and in a climate chamber (1.5%).

Closed Loop Physiological ECMO Control

Patients suffering acute lung failure depend on artificial ventilation in order to survive. In severe cases, this therapy may not be sufficient any more and long term extracorporeal membrane oxygenation (ECMO) may be used as a last chance rescue therapy. Adapted from short term cardiopulmonary bypass, these machines now need an increased ability for autonomous and unsupervised operation. Apart from the material aspects (hemolysis and long term biocompatibility), a prerequisite for safe and reliable operation is the implementation of an adequate automation and safety scheme. Extending previous work [1,2] where we focused on machine internal control and the modeling of the biological process, this paper presents an integrated control of the physiological target values.

Electrical Bioimpedance-Controlled Surgical Instrumentation

A bioimpedance-controlled concept for bone cement milling during revision total hip replacement is presented. Normally, the surgeon manually removes bone cement using a hammer and chisel. However, this procedure is relatively rough and unintended harm may occur to tissue at any time. The proposed bioimpedance-controlled surgical instrumentation improves this process because, for example, most risks associated with bone cement removal are avoided. The electrical bioimpedance measurements enable online process-control by using the milling head as both a cutting tool and measurement electrode at the same time. Furthermore, a novel integrated surgical milling tool is introduced, which allows acquisition of electrical bioimpedance data for online control; these data are used as a process variable. Process identification is based on finite element method simulation and on experimental studies with a rapid control prototyping system. The control loop design includes the identified process model, the characterization of noise as being normally distributed and the filtering, which is necessary for sufficient accuracy ( ±0.5 mm). Also, in a comparative study, noise suppression is investigated in silico with a moving average filter and a Kalman filter. Finally, performance analysis shows that the bioimpedance-controlled surgical instrumentation may also performs effectively at a higher feed rate (e.g., 5 mm/s).

Model-based supervision of a blood pump

Abstract In this paper, we present a novel method to supervise several discrete events and continuous processes causing failures in a blood pump. These are potential hazards which regularly cause problems in intensive care routine. We propose an indicator that considers the nonlinear shear thinning flow properties of blood. Based on a threefold of physiological motivated measures, we calculate an indicator which is not only able to detect ongoing events like gas in the blood phase but also to predict upcoming events like the suction of the withdrawing cannula to the surrounding vessels wall. We present an algorithm that is embedded in a distributed 32 bit microcontroller network and holding hard real-time constraints. We were able to evaluate out algorithms in-vivo. For this algorithm we analyzed online data of more than 140 hours of animal experiments.

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.

Decentralized safety concept for closed-loop controlled intensive care : Supervision of a blood pump during extracorporeal circulation

Abstract: This paper presents a decentralized safety concept for networked intensive care setups, for which a decentralized network of sensors and actuators is realized by embedded microcontroller nodes. It is evaluated for up to eleven medical devices in a setup for automated acute respiratory distress syndrome (ARDS) therapy. In this contribution we highlight a blood pump supervision as exemplary safety measure, which allows a reliable bubble detection in an extracorporeal blood circulation. The approach is validated with data of animal experiments including 35 bubbles with a size between 0.05 and 0.3 ml. All 18 bubbles with a size down to 0.15 ml are successfully detected. By using hidden Markov models (HMMs) as statistical method the number of necessary sensors can be reduced by two pressure sensors.

Physiological closed-loop control of mechanical ventilation and extracorporeal membrane oxygenation.

Abstract A new concept is presented for cooperative automation of mechanical ventilation and extracorporeal membrane oxygenation (ECMO) therapy for treatment of acute respiratory distress syndrome (ARDS). While mechanical ventilation is continuously optimized to promote lung protection, extracorporeal gas transfer rates are simultaneously adjusted to control oxygen supply and carbon dioxide removal using a robust patient-in-the-loop control system. In addition, the cooperative therapy management uses higher-level algorithms to adjust both therapeutic approaches. The controller synthesis is derived based on the introduced objectives, the experimental setup and the uncertain models. Finally, the autonomous ARDS therapy system capabilities are demonstrated and discussed based on in vivo data from animal experiments.

Modeling of Bioimpedance Spectroscopy Measurements for the Process Control of an Orthopedic Surgical Milling Tool

Surgical standard procedures such as the Revision Total Hip Replacement (RTHR) are essential to maintain individual mobility and life quality in aging industrial societies. As a consequence the number of these surgeries increases, but the used instruments do not guarantee the desired precision and application security in all cases. Due to this fact the integration of medical measurement methods like the Bioimpedance Spectroscopy (BIS), which is cheap, fast, accurate and unobtrusive, into surgical instruments for online process control and fault detection is suggested to solve this drawback. To improve this we developed an Impendence Controlled Surgical Instrument (ICOS), which enables BIS measurements during the Bone Cement (BC) removal by milling over the fast rotating milling head as active electrode. To establish BIS as a measured variable for the control setup we predict the BIS values for our ICOS in Finite Elements Method (FEM) simulations of the physiological operation scenario. Based on this an experimental in vitro setup is designed and validated with FEM simulations to enable the reproducible experiments and analysis of additional influencing variables. Beyond that we model the BC removal with a variable capacitive impedance in dependence of the residual BC thickness and a constant serial impedance offset. Finally we experimentally parameterize the model and a sensitivity analysis and first results of the feedback control will be given.

Bootstrap aggregating decision tree for motion classification based on a textile-integrated and wearable sensorarray

In this work a system for instant classification of motion patterns is presented. It is based on a non-contact magnetic induction monitoring device, which is textile-integrated, wearable, and able to measure pulse and respiratory activity. The proposed classificator is based on a decision tree algorithm generated by bootstrap aggregating. Its accurate classification performance is validated with the help of a data set comprising five exemplary motion patterns. Furthermore, the dependance of the misclassification error on the input sample length is investigated.

Femoral Test Bed for Impedance Controlled Surgical Instrumentation

The risk for patients during the standard procedure of revision of cemented artificial hip joints is unsatisfactorily highdue to its high level of invasiveness and limited access to the operative field. To reduce this risk we are developing anImpedance Controlled Surgical Instrumentation (ICOS) system, which aims to establish real-time control during a BoneCement (BC) milling process. For this, the relationship between the thickness of the BC and its frequency-dependentelectrical impedance is used to estimate the residual BC thickness. The aim is to avoid unintended cutting of boneby detecting the passage of the BC/bone boundary layer by the milling head. In a second step, an estimation of theresidual BC thickness will be used to improve process control. As a first step towards demonstrating the feasibility ofour approach, presented here are experimental studies to characterize the BC permittivity and to describe the process indetail. The results show that the permittivity properties of BC are dominated by its polymethyl methacrylate (PMMA)fraction. Thus, PMMA can be used as a substitute for future experiments. Furthermore, a Femoral Test Bed (FTB) wasdesigned. Using this setup we show it is feasible to accurately distinguish between slightly different thicknesses of BC.