André Stollenwerk

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.

A physiological model for extracorporeal oxygenation controller design

Long term extracorporeal membrane oxygenation can be used in cases of severe lung failure to maintain sufficient gas exchange without the need to apply higher ventilation pressures which damage the lung additionally. The use of cardiopulmonary bypass devices is well established inside the operating room. The usage of such devices as long-term support in the intensive care unit is still experimental and limited to few cases. This is because neither machine architecture nor staff situation provides for the long term application scenario. In the joint research Project “smart ECLA” we target an advanced ECMO device featuring an automation system capable of maintaining gas concentrations automatically. One key requirement for systematic controller design is the availability of a process model, which will be presented in this article.

An undergraduate embedded software laboratory for the masses

In addition to lectures on basic theoretical topics nowadays curricula demand more and more practical experiences from the students. Due to the so-called bologna process in Europe the graduation scheme at the department of computer science at RWTH Aachen University was changed, towards Bachelor and Master degrees. Within this change additional courses were established in order to improve the quality of education. The paper presents a lab course given at RWTH Aachen University already twice. It gives third semester bachelor students a first impression on creating embedded software. The course has to be attended by all undergraduate students. Due to the increasing number of students in computer science this will be up to 250 students, which is one of the biggest challenges of this course. In addition to embedded programming many system software concepts are practically implemented in this lab course. This enables the students to gain crucial knowledge in basic fields of computer science.

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.

ROBUST CONTROL OF END-TIDAL CO 2 USING THE H ∞ LOOP-SHAPING APPROACH

Mechanically ventilated patients require appropriate settings of respiratory control variables to maintain acceptable gas exchange. To control the carbon dioxide (CO 2 ) level effectively and automatically, system identification based on a human subject was performed using a linear affine model and a nonlinear Hammerstein structure. Subsequently, a robust controller was designed using the H ∞ loop-shaping approach, which synthesizes the optimal controller based on a specific objective by achieving stability with guaranteed performance. For demonstration purposes, the closed-loop control ventilation system was successfully tested in a human volunteer. The experimental results indicate that the blood CO 2 level may indeed be controlled noninvasively by measuring end-tidal CO 2 from expired air. Keeping the limited amount of experimental data in mind, we conclude that H ∞ loop-shaping may be a promising technique for control of mechanical ventilation in patients with respiratory insufficiency.

Automatisierung und Fehlerdiagnose bei der extrakorporalen Membranoxygenierung

Zusammenfassung Die Extrakorporale Membranoxygenierung ist eine der letzten Therapieoptionen für schwere Fälle eines akuten Lungenversagens. Hierzu wird Blut in einem externen Kreislauf ähnlich einer Herz-Lungen-Maschine durch einen Oxygenator gepumpt. In diesem findet ein zusätzlicher Gasaustausch statt. Im Gegensatz zum Einsatz im Operationssaal wird die länger andauernde Therapie auf der Intensivstation in der Regel nicht kontinuierlich durch einen Kardiotechniker überwacht. Die in diesem Beitrag vorgestellten Konzepte für Automatisierung und Fehlerdiagnose sind ein wichtiger Schritt hin zu einem sicheren und zuverlässigen teil-autonomen Betrieb eines Systems, das sich den individuellen Bedürfnissen des Patienten kontinuierlich anpasst.

Analyzing Embedded Systems Code for Mixed-Critical Systems Using Hybrid Memory Representations

This paper presents a low-level memory and hardware model suitable for analyzing embedded systems software written in high-level languages such as C. The key feature of this approach is that it combines information that can be discovered from the C code itself with information from the executable binary program. Further, it also integrates effects caused through hardware dependencies. We describe the benefits of this model by showing its applicability to thev erification of properties related to software partitioning, which is crucial for systems of mixed criticality. Furthermore, wede monstrate that our model can easily be integrated into abstract interpretation frameworks for high-level languages so as to increase analysis precision.

Smart Medical Information Technology for Healthcare (SMITH)

Summary Introduction: This article is part of the Focus Theme of Methods of Information in Medicine on the German Medical Informatics Initiative. “Smart Medical Information Technology for Healthcare (SMITH)” is one of four consortia funded by the German Medical Informatics Initiative (MI-I) to create an alliance of universities, university hospitals, research institutions and IT companies. SMITH’s goals are to establish Data Integration Centers (DICs) at each SMITH partner hospital and to implement use cases which demonstrate the usefulness of the approach. Objectives: To give insight into architectural design issues underlying SMITH data integration and to introduce the use cases to be implemented. Governance and Policies: SMITH implements a federated approach as well for its governance structure as for its information system architecture. SMITH has designed a generic concept for its data integration centers. They share identical services and functionalities to take best advantage of the interoperability architectures and of the data use and access process planned. The DICs provide access to the local hospitals’ Electronic Medical Records (EMR). This is based on data trustee and privacy management services. DIC staff will curate and amend EMR data in the Health Data Storage. Methodology and Architectural Framework: To share medical and research data, SMITH’s information system is based on communication and storage standards. We use the Reference Model of the Open Archival Information System and will consistently implement profiles of Integrating the Health Care Enterprise (IHE) and Health Level Seven (HL7) standards. Standard terminologies will be applied. The SMITH Market Place will be used for devising agreements on data access and distribution. 3LGM 2 for enterprise architecture modeling supports a consistent development process. The DIC reference architecture determines the services, applications and the standards-based communication links needed for efficiently supporting the ingesting, data nourishing, trustee, privacy management and data transfer tasks of the SMITH DICs. The reference architecture is adopted at the local sites. Data sharing services and the market place enable interoperability. Use Cases: The methodological use case “Phenotype Pipeline” (PheP) constructs algorithms for annotations and analyses of patient-related phenotypes according to classification rules or statistical models based on structured data. Unstructured textual data will be subject to natural language processing to permit integration into the phenotyping algorithms. The clinical use case “Algorithmic Surveillance of ICU Patients” (ASIC) focusses on patients in Intensive Care Units (ICU) with the acute respiratory distress syndrome (ARDS). A model-based decision-support system will give advice for mechanical ventilation. The clinical use case HELP develops a “hospital-wide electronic medical record-based computerized decision support system to improve outcomes of patients with blood-stream infections” (HELP). ASIC and HELP use the PheP. The clinical benefit of the use cases ASIC and HELP will be demonstrated in a change of care clinical trial based on a step wedge design. Discussion: SMITH’s strength is the modular, reusable IT architecture based on interoperability standards, the integration of the hospitals’ information management departments and the public-private partnership. The project aims at sustainability beyond the first 4-year funding period.

Enrichment of a diving computer with body sensor network data

Decompression algorithms in hyperbaric applications currently usually base on information about the ambient pressure in a temporal course. However, the impact of other factors like temperature or physical activity is well documented in literature. Therefore, we elaborated a prototypic setup, which is not only able to enrich the decompression algorithms run on a diving computer by this data, but also store this information for successive data mining.

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.