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Dive into the research topics where Tobias Wartzek is active.

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Featured researches published by Tobias Wartzek.


ubiquitous computing | 2011

The smart car seat: personalized monitoring of vital signs in automotive applications

Marian Walter; Benjamin Eilebrecht; Tobias Wartzek; Steffen Leonhardt

Embedded wireless sensors are important components of mobile distributed computing networks, and one of the target applications areas is health care. The preservation of mobility for senior citizens is one of the key issues in maintaining an independent lifestyle. Thus health technologies inside a car can contribute both to safety issues (supervision of driver fitness) as well as healthcare issues by monitoring vitals signs imperceptibly. In this paper, three embedded measurement techniques for non-contact monitoring of vital signals have been investigated. Specifically, capacitive electrocardiogram (cECG) monitoring, mechanical movement analysis (ballistocardiogram, BCG) using piezo-foils and inductive impedance monitoring were examined regarding their potential for integration into car seats. All three sensing techniques omit the need for electroconductive contact to the human body, but require defined mechanical boundary conditions (stable distances or, in the case of BCG, frictional connection). The physical principles of operation, the specific boundary conditions regarding automotive integration and the results during wireless operation in a running car are presented. All three sensors were equipped with local intelligence by incorporating a microcontroller. To eliminate the need for additional cabling, a wireless Bluetooth communication module was added and used to transmit data to a measurement PC. Finally, preliminary results obtained during test drives on German city roads and highways are discussed.


IEEE Transactions on Biomedical Engineering | 2011

ECG on the Road: Robust and Unobtrusive Estimation of Heart Rate

Tobias Wartzek; Benjamin Eilebrecht; Jeroen Lem; Hans-Joachim Lindner; Steffen Leonhardt; Marian Walter

Modern automobiles include an increasing number of assistance systems to increase the drivers safety. This feasibility study investigated unobtrusive capacitive ECG measurements in an automotive environment. Electrodes integrated into the driving seat allowed to measure a reliable ECG in 86% of the drivers; when only (light) cotton clothing was worn by the drivers, this value increased to 95%. Results show that an array of sensors is needed that can adapt to the different drivers and sitting positions. Measurements while driving show that traveling on the highway does not distort the signal any more than with the car engine turned OFF, whereas driving in city traffic results in a lowered detection rate due to the drivers heavier movements. To enable robust and reliable estimation of heart rate, an algorithm is presented (based on principal component analysis) to detect and discard time intervals with artifacts. This, then, allows a reliable estimation of heart rate of up to 61% in city traffic and up to 86% on the highway: as a percentage of the total driving period with at least four consecutive QRS complexes.


IEEE Transactions on Biomedical Engineering | 2011

Triboelectricity in Capacitive Biopotential Measurements

Tobias Wartzek; Thomas Lammersen; Benjamin Eilebrecht; Marian Walter; Steffen Leonhardt

Capacitive biopotential measurements suffer from strong motion artifacts, which may result in long time periods during which a reliable measurement is not possible. This study examines contact electrification and triboelectricity as possible reasons for these artifacts and discusses local triboelectric effects on the electrode-body interface as well as global electrostatic effects as common-mode interferences. It will be shown that most probably the triboelectric effects on the electrode-body interface are the main reason for artifacts, and a reduction of artifacts can only be achieved with a proper design of the electrode-body interface. For a deeper understanding of the observed effects, a mathematical model for triboelectric effects in highly isolated capacitive biopotential measurements is presented and verified with experiments. Based on these analyses of the triboelectric effects on the electrode-body interface, different electrode designs are developed and analyzed in order to minimize artifacts due to triboelectricity on the electrode-body interface.


IEEE Reviews in Biomedical Engineering | 2015

Ambient and Unobtrusive Cardiorespiratory Monitoring Techniques

Christoph Brüser; Christoph Hoog Antink; Tobias Wartzek; Marian Walter; Steffen Leonhardt

Monitoring vital signs through unobtrusive means is a goal which has attracted a lot of attention in the past decade. This review provides a systematic and comprehensive review over the current state of the field of ambient and unobtrusive cardiorespiratory monitoring. To this end, nine different sensing modalities which have been in the focus of current research activities are covered: capacitive electrocardiography, seismo- and ballistocardiography, reflective photoplethysmography (PPG) and PPG imaging, thermography, methods relying on laser or radar for distance-based measurements, video motion analysis, as well as methods using high-frequency electromagnetic fields. Current trends in these subfields are reviewed. Moreover, we systematically analyze similarities and differences between these methods with respect to the physiological and physical effects they sense as well as the resulting implications. Finally, future research trends for the field as a whole are identified.


Physiological Measurement | 2014

Bioelectrical impedance spectroscopy as a fluid management system in heart failure

Sören Weyer; Matthias Daniel Zink; Tobias Wartzek; Lennart Leicht; Karl Mischke; Thomas Vollmer; Steffen Leonhardt

Episodes of hospitalization for heart failure patients are frequent and are often accompanied by fluid accumulations. The change of the body impedance, measured by bioimpendace spectroscopy, is an indicator of the water content. The hypothesis was that it is possible to detect edema from the impedance data. First, a finite integration technique was applied to test the feasibility and allowed a theoretical analysis of current flows through the body. Based on the results of the simulations, a clinical study was designed and conducted. The segmental impedances of 25 patients suffering from heart failure were monitored over their recompensation process. The mean age of the patients was 73.8 and their mean body mass index was 28.6. From these raw data the model parameters from the Cole model were deduced by an automatic fitting algorithm. These model data were used to classify the edema status of the patient. The baseline values of the regression lines of the extra- and intracellular resistance from the transthoracic measurement and the baseline value of the regression line of the extracellular resistance from the foot-to-foot measurement were identified as important parameters for the detection of peripheral edema. The rate of change of the imaginary impedance at the characteristic frequency and the mean intracellular resistance from the foot-to-foot measurement were identified as important parameters for the detection of pulmonary edema. To classify the data, two decision trees were considered: One should detect pulmonary edema (n(pulmonary) = 13, n(none) = 12) and the other peripheral edema (n(peripheral) = 12, n(none) = 13). Peripheral edema could be detected with a sensitivity of 100% and a specificity of 90%. The detection of pulmonary edema showed a sensitivity of 92.31% and a specificity of 100%. The leave-one-out cross-validation-error for the peripheral edema detection was 12% and 8% for the detection of pulmonary edema. This enables the application of BIS as an early warning system for cardiac decompensation with the potential to optimize patient care.


IEEE Journal of Biomedical and Health Informatics | 2014

Robust Sensor Fusion of Unobtrusively Measured Heart Rate

Tobias Wartzek; Christoph Brüser; Marian Walter; Steffen Leonhardt

Contactless vital sign measurement technologies often have the drawback of severe motion artifacts and periods in which no signal is available. However, using several identical or physically different sensors, redundancy can be used to decrease the error in noncontact heart rate estimation, while increasing the time period during which reliable data are available. In this paper, we show for the first time two major results in case of contactless heart rate measurements deduced from a capacitive ECG and optical pulse signals. First, an artifact detection is an essential preprocessing step to allow a reliable fusion. Second, the robust but computationally efficient median already provides good results; however, using a Bayesian approach, and a short time estimation of the variance, best results in terms of difference to reference heart rate and temporal coverage can be achieved. In this paper, six sensor signals were used and coverage increased from 0-90% to 80-94%, while the difference between the estimated heart rate and the gold standard was less than ±2 BPM.


IEEE Transactions on Biomedical Circuits and Systems | 2013

Impedance Measurement System for Determination of Capacitive Electrode Coupling

Benjamin Eilebrecht; Johannes Willkomm; Antje Pohl; Tobias Wartzek; Steffen Leonhardt

Capacitive electrodes have been studied as an alternative to gel electrodes, as they allow measurement of biopotentials without conductive contact with the patient. However, because the skin interface is not as precisely defined as with gel electrodes, this could lead to signal deformation and misdiagnoses. Thus, measurement of a capacitive coupling of the electrodes may allow to draw conclusions about the applicability of such systems. In addition, combining capacitive biosignal sensing with an impedance measurement unit may enable bioimpedance measurements, from which additional information on the hydration status can be extracted. A prototype system is introduced which measures impedance over capacitive electrodes in parallel with biopotential measurements. Also presented are the first results on characterization of the skin electrode coupling achieved with the system.


Archive | 2011

Motion Artifact Removal from Capacitive ECG Measurements by Means of Adaptive Filtering

Benjamin Eilebrecht; Tobias Wartzek; Johannes Willkomm; A. Schommartz; Marian Walter; Steffen Leonhardt

Capacitive ECG sensing is not just a very promising alternative to conventional ECG but also allows for new applications, in which recording a conventional ECG is not imaginable due to practical aspects. This way, integration into car seats for monitoring of the heart rate of the driver or a usage in a home monitoring scenario is no longer unimaginable. Nevertheless, capacitive ECG measurements are very prone to motion artifacts, which need to be eliminated. For this purpose, this paper introduces adaptive filtering as a method for signal enhancement by using a second signal, which is correlated with the interfering signal. The approach is validated in a setting with an additional acceleration signal during car drive.


Archive | 2009

Implementation of a capacitive ECG measurement system in clinical practice: an interim report

Benjamin Eilebrecht; Michael Czaplik; Marian Walter; Tobias Wartzek; Rolf Rossaint; Steffen Leonhardt

This paper presents the first results about the acceptance of a capacitive ECG measurement system on the clinicians as well as on the patient side. In a clinical study an ECG measurement system with capacitively coupled electrodes was tested against a conventional reference ECG. The whole setup including study design, description of the measurement and clinical setup as well as the results about acceptance and first diagnostic are presented and the use in different application scenarios is discussed.


international conference of the ieee engineering in medicine and biology society | 2010

A capacitive ECG array with visual patient feedback

Benjamin Eilebrecht; Antje Schommartz; Marian Walter; Tobias Wartzek; Michael Czaplik; Steffen Leonhardt

Capacitive electrocardiogram (ECG) sensing is a promising technique for less constraining vital signal measurement and close to a commercial application. Even bigger trials testing the diagnostic significance were already done with single lead systems. Anyway, most applications to be found in research are limited to one channel and thus limited in its diagnostic relevance as only diseases coming along with a change of the heart rate can be diagnosed adequately. As a consequence the need for capacitive multi-channel ECGs combining the diagnostic relevance and the advantages of capacitive ECG sensing emerges. This paper introduces a capacitive ECG measurement system which allows the recording of standardized ECG leads according to Einthoven and Goldberger by means of an electrode array with nine electrodes.

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Jutta Arens

RWTH Aachen University

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