Inga Margrit Elixmann

Hirndruckmodellierung und Regelung einer neuen mechatronischen externen Ventrikeldrainage

Zusammenfassung Die Ableitung von Hirnwasser durch externe Ventrikeldrainagen ist eine lebensnotwendige Maßnahme bei akutem Hirndruckanstieg und wird bisher in der Regel rein mechanisch umgesetzt. Die neu entwickelte und hier vorgestellte mechatronische Ventrikeldrainage regelt den Hirndruck und ermöglicht dem Patienten damit eine zuverlässigere Therapie. Das Drainagekonzept erlaubt dem Arzt eine umfassendere Beobachtung des Krankheitsverlaufs durch die Darstellung wichtiger Parameter wie Hirndruck, drainiertem Hirnwasserfluss und Compliance. Für die Regelung der externen Ventrikeldrainage wurde eine statische Teilkompensation des nichtlinearen Prozesses mit einem PI-Anteil kombiniert und simulativ erprobt. Im Einsatz an einem Menschmodell-Prüfstand konnte die geregelte Ventrikeldrainage die vorgegebenen Regelziele erfüllen. Abstract The drainage of cerebrospinal fluid by an external ventricular drainage is an indispensable therapy for acute brain pressure rise which at present is realized commonly with purely mechanical devices. The new drainage concept presented in this work uses a mechatronic device with automatic pressure control to enable a more reliable and automated therapy for the patient and a comprehensive examination of the disease for the doctor by the monitoring of the important parameters brain pressure, drained cerebrospinal fluid and compliance. To control the ventricular drainage, a partial static compensation of the process nonlinearity was combined with a proportional integral controller. This controller was tested in simulations and in a human-like test rig. The controlled ventricular drainage was able to achieve all brain pressure control targets.

Control of an electromechanical hydrocephalus shunt--a new approach.

Hydrocephalus is characterized by an excessive accumulation of cerebrospinal fluid (CSF). Therapeutically, an artificial pressure relief valve (so-called shunt) is implanted which opens in case of increased intracranial pressure (ICP) and drains CSF into another body compartment. Today, available shunts are of a mechanical nature and drainage depends on the pressure drop across the shunt. According to the latest data, craniospinal compliance is considered to be even more important than mean ICP alone. In addition, ICP is not constant but varies due to several influences. In fact, heartbeat-related ICP waveform patterns depend on volume changes in the cranial vessels during a heartbeat and changes its shape as a function of craniospinal compliance. In this paper, we present an electromechanical shunt approach, which changes the CSF drainage as a function of the current ICP waveform. A series of 12 infusion tests in patients were analyzed and revealed a trend between the compliance and specific features of the ICP waveform. For waveform analysis of patient data, an existing signal processing algorithm was improved (using a Moore machine) and was implemented on a low-power microcontroller within the electromechanical shunt. In a test rig, the ICP waveforms were replicated and the decisions of the ICP analysis algorithm were verified. The proposed control algorithm consists of a cascaded integral controller which determines the target ICP from the measured waveform, and a faster inner-loop integral controller that keeps ICP close to the target pressure. Feedforward control using measurement data of the patients position was implemented to compensate for changes in hydrostatic pressure during change in position. A model-based design procedure was used to lay out controller parameters in a simple model of the cerebrospinal system. Successful simulation results have been obtained with this new approach by keeping ICP within the target range for a healthy waveform.

Single pulse analysis of intracranial pressure for a hydrocephalus implant

The intracranial pressure (ICP) waveform contains important diagnostic information. Changes in ICP are associated with changes of the pulse waveform. This change has explicitly been observed in 13 infusion tests by analyzing 100 Hz ICP data. An algorithm is proposed which automatically extracts the pulse waves and categorizes them into predefined patterns. A developed algorithm determined 88%±8% (mean ±SD) of all classified pulse waves correctly on predefined patterns. This algorithm has low computational cost and is independent of a pressure drift in the sensor by using only the relationship between special waveform characteristics. Hence, it could be implemented on a microcontroller of a future electromechanic hydrocephalus shunt system to control the drainage of cerebrospinal fluid (CSF).

IN-VITRO EVALUATION OF A DRAINAGE CATHETER WITH INTEGRATED BIOIMPEDANCE ELECTRODES TO DETERMINE VENTRICULAR SIZE

Patients suffering from Hydrocephalus show an increased accumulation of cerebrospinal fluid, which needs to be drained into another body compartment by an im- planted shunt. To prevent from over-drainage, which some- times still occurs despite improvements in shunt technology, a possible future shunt could contain sensors and supervise the ventricular size electrically. This work approaches this and presents the in vitro study of a drainage catheter with integrated bioimpedance evaluation capabilities.

Simulation of existing and future electromechanical shunt valves in combination with a model for brain fluid dynamics.

Several models are available to simulate raised intracranial pressure (ICP) in hydrocephalus. However, the hydrodynamic effect of an implanted shunt has seldom been examined. In this study, the simple model of Ursino and Lodi [14]is extended to include (1) the effect of a typical ball-in-cone valve, (2) the effect of the size of the diameter of the connecting tube from valve to abdomen, and (3) the concept of a controlled electromechanical shunt valve in overall cerebrospinal fluid dynamics.By means of simulation, it is shown how a shunt can lower ICP. Simulation results indicate that P and B waves still exist but at a lower ICP level and that, due to the exponential pressure-volume curve, their amplitude is also considerably lowered. A waves only develop if the valve is partially blocked. The resulting ICP is above the opening pressure of the valve, depending on the drain and resistance of the shunt.The concept of a new electromechanical shunt was more successful than the traditional mechanical valves in keeping ICP at a desired level. The influence of the patients movements or coughing on ICP as well as the body position affecting the reference ICP, which can be measured, has not yet been modeled and should be addressed in future using suitable algorithms.

Robust Control of Intracranial Pressure with an Electromechanical Extra-ventricular Drainage

The drainage control of cerebrosprinal fluid, as needed in the treatment of increased intracranial pressure, is to this day achieved manually by using an external ventricular drainage system. The manual control procedure bears several risks for the patient among which the rapid decrease of intracranial pressure induced by patients upper body inclination angle change is the most prominent. An automatic controller is suggested to increase patients safety and the quality of the therapy by delivering a continuous pressure control and the rejection of disturbances like cerebrospinal fluid production rate and inclination angle changes. In this contribution an intracranial pressure controller is designed using the robust control methodology and subsequently validated in nonlinear simulations and in a hydrodynamic human cerebral simulator. The controller is designed using a mixed uncertainty approach accounting for uncertainties in the technical and the physiological system. A self-scheduled implementation of the controller guarantees the compensation of the nonlinear input function for the process, being of Hammer stein structure. The controller shows stable response in simulations and Mock experiments for various operating points and disturbance rejection tests.

Transcutaneous Energy Transfer System Incorporating a Datalink for a Wearable Autonomous Implant

This paper presents a newly developed Transcutaneous Energy Transfer (TET) System to supply an electromechanical implant with energy. The system is capable of delivering a power of 1-5 W to the implant over a distance of up to 5 cm via an inductive link with a frequency of 100 kHz. Additionally, the inductive link incorporates a data link which allows transmission of measurement data and information regarding the link quality. Because of the integration of power transfer and data transfer the system is thus energy saving in comparison to most TET systems, which often need an additional second dedicated radio communication channel. For the data transmission from the energy transmitter to the implant frequency shift keying and from the implant to the energy transmitter load modulation has been implemented.

Analyse und Regelung des Hirndrucks beim Hydrozephalus

Das folgende Kapitel widmet sich dem Thema des Hirndrucks und technischen Medizinprodukten, die diesen bei Bedarf therapeutisch beeinflussen konnen. Ziel dieses Kapitels ist es, Grundlagen zum Thema des Hirndrucks inklusive Messtechnik zu vermitteln und Pathologien mit resultierendem erhohten Hirndruck zu erlautern, die eine Therapie benotigen. Es soll anhand eines historischen Uberblicks vermittelt werden, wie sich therapeutische Masnahmen durch Hirnwasser-Drainagesysteme zur Hirndruckreduktion uber die Zeit entwickelt haben und anhand eines Beispiels gezeigt werden, wie diese durch Modellbildung simulativ evaluiert werden konnen.

Design and Evaluation of an Automatic Extraventricular Drainage Control System

Until this day, the drainage of cerebrospinal fluid, as necessary in case of an acute increased intracranial pressure, is conducted manually by adjusting the hydrostatic height of an external drainage bag. The associated problems with the manual open-loop control strategy are an increasing pressure error over time periods involving no correction and the inherent risk of an overdrainage, which may occur, for example, after changes of the patients upper body inclination angle. In this paper, an automatic control strategy is suggested to alleviate these problems thereby increasing the patients safety and the overall quality of the therapy. The automatic controller presented in this paper is designed for our newly developed intelligent external ventricular drainage system. The proposed controller has to guarantee robustness and performance in face of uncertain patient intracranial dynamics and nonlinearities associated with the actuator. The controller is thus designed to guarantee robust performance using a mixed uncertainty modeling approach and extended by a self-scheduling approach to compensate for input nonlinearities. Controller performance is validated in nonlinear simulations, an experimental test setup, and animal experiments, involving pigs with an artificially induced hydrocephalus.

FIRST RESULTS OF A NEW ELECTROMECHANICAL CONTROLLED EXTERNAL VENTRICULAR DRAINAGE IN A PORCINE MODEL

Acute increase of intracranial pressure (ICP) usually has to be treated with an external ventricular drainage (EVD). Current standard mechanical EVD carry a lot of disadvantages, which hypothetically could be bet- ter managed by a newly developed electromechanical EVD. In this report our first preliminary results of such an elec- tromechanical EVD applied in a porcine animal model are presented. The drainage was demonstrated to be both suc- cessful in monitoring and controlling elevated ICP, and able to detect slit ventricles due to overdrainage, if the indented target ICP was set too low.