Axel Cordes

Electric impedance tomography for monitoring volume and size of the urinary bladder.

Abstract A novel non-invasive technique for monitoring fluid content in the human bladder is described. Specifically, a precommercial electric impedance tomograph (EIT) was applied to measure and visualize impedance changes in the lower torso due to changes in bladder volume. Preliminary measurements were conducted during routine urodynamic tests of nine male paraplegic patients, in whom a contrast agent was slowly infused into the bladder for diagnostic purposes. In some patients, a good correlation between bladder volume and EIT measurements was found, whereas in others the correlation was still good but inverted, presumably due to a poor electrode positioning. These preliminary results indicate that a sufficiently accurate finite element modeling of the impedance distribution in the abdomen, and proper electrode positioning aids, are important prerequisites to enable this technology to be used for routine measurement of bladder volume.

[Non-contact monitoring of heart and lung activity using magnetic induction measurement in a neonatal animal model].

Zusammenfassung Hintergrund: Die magnetische Bioimpedanzmessung (MBM) ermöglicht die Bestimmung des Widerstandes in biologischem Gewebe mit Hilfe von magnetischen Wechselfeldern, d.h. sich zeitlich ändernden Magnetfeldern. Diese entstehen, wenn im Körper leitende Fluide bei Atemtätigkeit (Luft, schlecht leitend) oder Herzaktion (Blut, gut leitend) verschoben werden. Als Folge verändert sich die Widerstandsverteilung im Thorax, und es kommt zur Verschiebung seines Gesamtwiderstandes. Mittels Spulen werden diese Veränderungen kontaktlos registriert und aufgezeichnet. Dieses Messprinzip wurde bisher in einem Tiermodell mit ausgewachsenen Schweinen und bei gesunden Erwachsenen angewandt. Ein neonatales Tiermodell existiert nicht. Unser Ziel war es, mittels MBM kontaktlos Atemtätigkeit und Herzaktion bei neugeborenen Ferkeln zu messen, um dieses Verfahren gegebenenfalls als Modell zur Evaluation von Störungen der Herz- und Atemfunktion im Neugeborenenalter zu testen. Material und Methode: Mittels 5 Spulen (3 Mess- und 2 Erregerspulen) im Boden eines Experimentalinkubators wurde bei 16 analgosedierten Ferkeln simultan die Veränderung der magnetischen Induktion in Abhängigkeit von Herzaktion und Atemtätigkeit gemessen und mit einem Pulsoxymeter (Monitorsystem Sirecust 404 N) und einem Atemflussdetektor (Strömungswiderstand und Differenzdrucksensor) als Referenzsignale verglichen. Neben Spontanatmung wurden die Tiere unter Continuous Positive Airway Pressure (CPAP, Atemunterstützung zur Verhinderung des endexpiratorischen Alveolarkollapses,) (Flow 8 l/min, PEEP 5 cm H2O), konventioneller Beatmung (inspiratorischer Druck 14 mm Hg, Frequenz 40/min) und Hochfrequenzoszillation (HFOV, Beatmungsverfahren bei Lungenversagen) (Frequenz 10 Hz, Mitteldruck 10 mm Hg, Amplitude 1,5) untersucht. Die Erkennung der Atemtätigkeit durch MBM, im Vergleich zum Referenzsignal, wurde anhand der prozentualen Detektionsrate „korrekt registrierter Atemzüge“ (95-%-Konfidenzintervall) beurteilt. Zur Quantifizierung der Übereinstimmung zwischen MBM und Referenzmessung in der Herzfrequenz wurden der Konkordanzkorrelationskoeffizient (KKK) nach Lin (95% Konfidenzintervall) und der Bland-Altman-Plot herangezogen. Ergebnisse und Diskussion: Die Detektionsrate der Atemtätigkeit für MBM im Vergleich zum Referenzsignal lag unter CPAP bei 88% [95% KI: (87,1%; 88,5%)], unter konventioneller Beatmung bei 91% [95% KI: (90,3%; 91,2%)] und unter HFOV bei 95% [95% KI: (94,7%; 94,9%)]. Bei der Herzaktion lag während der Apnoephasen die Differenz bei 1,1 Schlägen/min (±11,3 SD) und unter HFOV bei 5,3 Schlägen/min (±26,4 SD). Unter Spontanatmung gelang es bisher nicht, eine Korrelation zwischen MBM und Referenzsignal herzustellen. Aufgrund von Interferenzproblemen war eine Erfassung der Herzaktion nur während Apnoephasen und unter HFOV möglich. Schlussfolgerung: Die Erfassung der Atemtätigkeit mittels MBM ist in einem neonatalen Tiermodell grundsätzlich möglich. Aufgrund der viel kleineren Herzsignal-anteile gelingt die Herzaktivität bisher nur in ausgewählten Situationen. Die Ergebnisse können eine Basis für die Entwicklung von wenig- bzw. nichtinvasiven Parametern in der Neonatologie sein, wobei als nächstes qualitative Eigenschaften der Atemtätigkeit erfasst werden sollten. Abstract Background: Magnetic induction measurement (MIM) allows the identification of resistance in biologic tissues by alternating magnetic fields. These occur when well-conducting (blood) and poor-conducting matter (air) is moved through the thorax during heart and lung activity. As a result, allocation of the resistance changes and the total resistance of the thorax is shifted. By using coils, these changes can be registered in a non-contact manner and recorded. To date, this measuring principle was employed only in adult volunteers or in full-grown pigs. A neonatal animal model has not yet been described. The aim of this study was to test the hypothesis that non-contact monitoring of heart and lung activity using MIM in a porcine newborn piglet model can be applied in order to evaluate neonatal disorders of heart and lung activity in the future. Materials and methods: By using five coils (three measurement and two excitation coils), placed at the bottom of an experimental incubator, magnetic induction changes, depending on the heart and lung activity in 16 analgosedated piglets, were simultaneously measured and compared with pulse oximetry and airflow detection (flow resistance and pressure differential sensor) as reference signals. In addition, spontaneous breathing, including apnea, CPAP (continuous positive airway pressure to prevent end-expiratory alveolar collapse, flow 8 l/min; pressure 5 cm H2O), mechanical ventilation (inspiratory pressure 14 cm H2O; frequency 40/min) and high frequency oxygenation ventilation (HFOV, ventilation method in lung failure) (frequency 10 Hz, mean pressure 10 cm H2O, amplitude 1.5) were performed. Lung activity with MIM compared with the reference signal was estimated with a detection rate (%) of “correct registered lung activity”. To quantify the analogy between MIM and reference signal for heart activity, the concordance correlation coefficient after Lin (95% confidence interval) and the Bland-Altman plot were calculated. Results and discussion: The detection rate for breathing [%] of MIM compared with the reference signal under CPAP was 88% [95% CI: (87.1%; 88.5%)], mechanical ventilation 91% [95% CI: (90.3%; 91.2%)] and under HFOV 95% [95% CI: (94.7%; 94.9%)]. For heart activity, during apnea the difference between MIM and reference signal was 1.1 bpm (±11.3 SD) in apnea and during HFOV 5.3 bpm (±26.4 SD). Under spontaneous breathing it was not possible to achieve a correlation. Owing to interference problems, registration of heart activity with MIM during simultaneous breathing activity (CPAP, conventional mechanical ventilation, HFOV) was insufficient. Conclusion: Non-contact monitoring of lung activity using MIM in a neonatal piglet model is possible under specific conditions. These results might be a basis for the development of non-invasive parameters in neonatology. It also provides the possibility of obtaining more information about the characteristics of lung activity of the newborn.

A portable magnetic induction measurement system (PIMS).

Abstract For contactless monitoring of ventilation and heart activity, magnetic induction measurements are applicable. As the technique is harmless for the human body, it is well suited for long-term monitoring solutions, e.g., bedside monitoring, monitoring of home care patients, and the monitoring of persons in critical occupations. For such settings, a two-channel portable magnetic induction system has been developed, which is small and light enough to be fitted in a chair or bed. Because demodulation, control, and filtering are implemented on a front-end digital signal processor, a PC is not required (except for visualization/data storage during research and development). The system can be connected to a local area network (LAN) or wireless network (WiFi), allowing to connect several devices to a large monitoring system, e.g., for a residential home for the elderly or a hospital with low-risk patients not requiring standard ECG monitoring. To visualize data streams, a Qt-based (Qt-framework by Nokia, Espoo, Finland) monitoring application has been developed, which runs on Netbook computers, laptops, or standard PCs. To induce and measure the magnetic fields, external coils and amplifiers are required. This article describes the system and presents results for monitoring respiration and heart activity in a (divan) bed and for respiration monitoring in a chair. Planar configurations and orthogonal coil setups were examined during the measurement procedures. The measurement data were streamed over a LAN to a monitoring PC running Matlab (The MathWorks Inc, Natick, MA, USA).

Breathing detection with a portable impedance measurement system: First measurements

For monitoring the health status of individuals, detection of breathing and heart activity is important. From an electrical point of view, it is known that breathing and heart activity change the electrical impedance distribution in the human body over the time due to ventilation (high impedance) and blood shifts (low impedance). Thus, it is possible to detect both important vital parameters by measuring the impedance of the thorax or the region around lung and heart. For some measurement scenarios it is also essential to detect these parameters contactless. For instance, monitoring bus drivers health could help to limit accidents, but directly connected systems limit the drivers free moving space. One measurement technology for measuring the impedance changes in the chest without cables is the magnetic impedance tomography (MIT). This article describes a portable measurement system we developed for this scenario that allows to measure breathing contactless. Furthermore, first measurements with five volunteers were performed and analyzed.

Development of a Portable Impedance Tomography System (PITS)

This paper shows a first concept on the realization of a Portable Impedance Tomography System (PITS). It works with alternating magnetic fields, induced into the patient’s body, to determine the tissue impedance without contact. The whole system, including the hardware configuration, measurement software and a discussion on gathered results, is treated in this work.

Magnetic induction measurements with a six channel coil array for vital parameter monitoring

Vital parameter monitoring on neonatal intensive care units is essential but very stressful for patients during daily routine care. For contact-less monitoring of breathing and heart activity, magnetic induction measurements are applicable in research scenarios. For monitoring both vital parameters in newborn intensive care wards, we developed a Multi Channel Simultaneous Magnetic Induction Measurement System (MUSIMITOS2+). In this article we now evaluate the technical requirements of a coil array for vital parameter monitoring and finally present a multichannel coil array with 6 excitation and measurement channels combined as axial gradiometers for the specific measurement scenario. This array will be stored underneath the child. As a test case we will present data of a animal trial with the described coil array and the measurement device MUSIMITOS2+.

Development of a device for measuring the sensitivity area of coil arrays for magnetic induction measurements

Combining single coils to form a coil array provide advantages for magnetic induction measurements of breathing or heart activity. The main goal for such combination could be a coil configuration which makes the whole measurement system less sensitive for moving artifacts of the patient due to the capability of using many coils for signal acquisition. Such setup could be designed and tested with FEM software. But in most cases, the technical realization differs from theoretical, for instance due to cable effects or the presence of amplifiers attached very close to the coils. Thus, a measurement system for detecting the sensitive area of real arrays is required. In this article, such a device is presented. Based on a crane construction, it is well suited for testing arrays which are built for an integration under a bed or within an incubator for vital parameter monitoring. We will describe the construction as well as first example measurements of a test array.

A full digital magnetic induction measurement device for non-contact vital parameter monitoring (MONTOS)

Magnetic induction measurements enable contactless monitoring of breathing and heart activity. Since this technique is in the scope of many research groups, there are several research devices available. Most of these devices are suitable for tomography approaches, e.g. edema detection or for monitoring technical processes, such as fluid in tubes or metal blocks. However, these devices are less useable for vital parameter monitoring. In this article, we present an new modular magnetic induction measurement system called MONTOS (Monitoring System) for this scenario. Since the implementation is fully digital, each module can easily be applied to several measurement conditions in vital parameter monitoring, i.e. Multi-Frequency measurement modes, Single-Excitation and Multiple-Measurements or Multiple-Excitation and Single-Measurement. Data output is realized via local area networks (LAN), thereby streaming the data to a monitoring computer. Finally, it will be demonstrated that impedance changes due to breathing of a human adult can be detected.

A neonatal thorax phantom for contact-less magnetic induction vitalparameter monitoring

For contact-less monitoring of breathing and heart activity, magnetic induction measurements are applicable. For research and the development process of hardware and algorithms for parameter extraction, test cases are computer simulations, animal trials and, at the end, human trials. However, in the first development processes human trials are not suitable due to ethical reasons. Simliarly, animal trials may not be reasonable for only testing different amplifier approaches or basic testing of new coil configurations. There, computer simulations are the only available benchmarks but not suitable for every problem. In this article, we present a neonatal thorax phantom for emulation of lung and heart activity for magnetic induction systems as a test platform.

Comparison of different coil positions for ventilation monitoring with contact-less magnetic impedance measurements

For monitoring the health status of individuals, proper monitoring of ventilation is desirable. Therefore, a continuous measurement technique is an advantage for many patients since it allows personal home care scenarios. As an example, monitoring of elderly people at home could enable them to live in their familiar environment on their own with the safety of a continuous monitoring. Therefore, a measurement technique without the restriction of mobility is required. Since it is possible to monitor ventilation with magnetic impedance measurements without conductive contact, this technique is well suited for the mentioned scenario. Integrated in a chair, a persons health state could be monitored in many situations, e.g. during meals, while watching TV or reading a book. In this paper, we compare different positions of coil arrays for a magnetic impedance measurement system integrated in a chair in order to monitor ventilation continuously. For limiting the costs and technical complexity of the magnetic impedance measurement system, we have a focus on coil configurations with one RF channel. To limit the needed space and thickness of the array in the backrest, planar gradiometer coil setups are investigated. All measurements will be performed with a new developed portable magnetic impedance measurement system and a standard office chair.