Benjamin Eilebrecht

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

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.

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

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.

Triboelectricity in Capacitive Biopotential Measurements

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.

Non-contact monitoring techniques - Principles and applications

This work gives an overview about some non-contact methods for monitoring of physiological activity. In particular, the focus is on ballistocardiography, capacitive ECG, Infrared Thermography, Magnetic Impedance Monitroing and Photoplethymographic Imaging. The principles behind the methods are described and an inside into possible medical applications is offered.

Impedance Measurement System for Determination of Capacitive Electrode Coupling

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.

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

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.

Clinical proof of practicability for an ECG device without any conductive contact

Abstract Heart rhythm disturbances are common symptoms of several heart disorders. One of the most effective screening methods is the traditional electrode-based ECG. However, this examination can be both time- and resource-consuming. Capacitive-coupling ECG (cECG) screening – working without any conductive electrical contact with the patient – might help to shorten the time required for diagnosis. In this study, we examine the practicability of employing a non-contact capacitive ECG in a clinical setting. A total of 30 volunteer patients aged over 50 years without pacemakers were included in our trial, after obtaining their written informed consent and their medical history. A cECG as well as a conventional, conductive ECG were recorded simultaneously. In addition to mathematical analysis, ECG data were manually evaluated by two clinicians blinded to the recording method and patient conditions. Data from 30 patients were collected during our study, seven of whom had experienced myocardial infarction. The obtained cECG signals showed a high correlation with the simultaneously recorded Einthoven lead II of the conventional ECG. The values for heart rate, PQ and QT time periods correlated particularly well. Significant differences were observed with regard to QRS duration. Data recorded in the supine position contained less motion artefacts and, in particular, there were fewer breathing artefacts compared to data collected from those in a sitting position. Owing to the easy and quick application of the cECG system, the feedback from the examined patients was consistently positive. In conclusion, recording cECG data in a sitting position provided sufficient quality for screening purposes. Further studies will be needed for the evaluation of cECG appropriateness in diagnosing heart disease.

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

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.

A capacitive ECG array with visual patient feedback

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.

Automatic electrode selection in unobtrusive capacitive ECG measurements

Due to the demographic change and increased cost pressure, contactless measurement methods such as capacitive ECG become more and more interesting in research and industry. As these electrodes shall be integrated in objects of daily life to unobtrusively monitor patients (e.g. a chair or a bed), one major problem arises: no medical expert attaches the electrodes and it is a priori not known to which electrodes the patient will have the best contact. Hence, several electrodes are usually integrated and this paper proposes a simple but robust method to automatically select the best coupled electrodes for the deduction of an ECG. It uses the driven right leg (DRL)-electrode to capacitively inject a high frequency voltage into the patient which is then capacitively received and analysed by each electrode. The electrodes with the largest high frequency signal are then used for the deduction of the ECG.