A multichannel portable ECG system with capacitive sensors

In-ovo imaging using ostrich eggs: Biomagnetism for detection of cardiac signals and embryonal motion

In-ovo imaging using ostrich eggs has been described as a potential alternative to common animal testing. The main advantage is its independence from small animal imaging devices as ostrich eggs provide good image quality on regular CT, MRI, or PET used in examinations of humans. However, embryonal motion during dynamic imaging studies produce artifacts. The aims of this study were (1) to explore the feasibility of biomagnetism to detect cardiac signals and embryonal motion and to use these findings (2) to investigate the effect of isoflurane anesthesia on ostrich embryos. A standard magnetoencephalography developed for brain studies was used to detect embryonal signals of ostrich eggs on developmental day 34. Signals were instantly shown on a screen and data were also postprocessed. For assessing the effects of anesthesia, nine ostrich eggs were investigated using isoflurane 6% for 90 min. Biomagnetic signals were recorded simultaneously. A control group consisting of eight different ostrich eggs was also investigated. Cardiac signals similar to electrocardiography were observed in all eggs. Postprocessing revealed frequent motion of embryos without anesthesia. The exposure to isoflurane led to a significant decrease in motion signals in 9/9 ostrich embryos after 8 min. Motion was significantly reduced in the isoflurane group versus control group. There were no isoflurane-related deaths. This study shows that biomagnetism is feasible to detect cardiac signals and motion of ostrich embryos in-ovo. Application of isoflurane is safe and leads to a rapid decrease in embryonal motion, which is an important prerequisite for the implementation of in-ovo imaging using ostrich eggs.

Novel Stable Capacitive Electrocardiogram Measurement System

This study presents a noncontact electrocardiogram (ECG) measurement system to replace conventional ECG electrode pads during ECG measurement. The proposed noncontact electrode design comprises a surface guard ring, the optimal input resistance, a ground guard ring, and an optimal voltage divider feedback. The surface and ground guard rings are used to reduce environmental noise. The optimal input resistor mitigates distortion caused by the input bias current, and the optimal voltage divider feedback increases the gain. Simulated gain analysis was subsequently performed to determine the most suitable parameters for the design, and the system was combined with a capacitive driven right leg circuit to reduce common-mode interference. The present study simulated actual environments in which interference is present in capacitive ECG signal measurement. Both in the case of environmental interference and motion artifact interference, relative to capacitive ECG electrodes, the proposed electrodes measured ECG signals with greater stability. In terms of R-R intervals, the measured ECG signals exhibited a 98.6% similarity to ECGs measured using contact ECG systems. The proposed noncontact ECG measurement system based on capacitive sensing is applicable for use in everyday life.

Quality evaluation of signals collected by portable ECG devices using dimensionality reduction and flexible model integration

OBJECTIVE

Portable devices for collecting electrocardiograms (ECGs) and telemedicine systems for diagnosis are available to residents in deprived areas, but ECGs collected by non-professionals are not necessarily reliable and may impair the accuracy of diagnosis. We propose an algorithm for accurate ECG quality assessment, which can help improve the reliability of ECGs collected by portable devices.

APPROACH

Using challenge data from CinC (2019), signals were classified as 'acceptable' and 'unacceptable' by annotators. The training set contained 998 12-lead ECGs and the test set contained 500. A 998 × 84 feature matrix, S, was formed by feature extraction and three basic models were obtained through training SVM, DT and NBC on S. The feature subsets S1, S2 and S3 were obtained by dimensionality reduction on S using SVM, DT and NBC, respectively. Three other basic models were obtained through training SVM on S1, DT on S2 and NBC on S3. By combining these six basic models, several integrated models were formed. An iterative method was proposed to select the integrated model with the highest accuracy on the training set. Having compared differences between the output labels and the original data labels, evaluation criteria were calculated.

MAIN RESULTS

An accuracy of 98.70% and 98.60% was achieved on the training and test datasets, respectively. High F1 score and Kappa values were also obtained.

SIGNIFICANCE

The proposed algorithm has advantages over previously reported approaches during automatic assessment of ECG quality and can thus help to reduce reliance on highly trained professionals when assessing the quality of ECGs.

Bioelectronic properties of DNA, protein, cells and their applications for diagnostic medical devices

From a couple of centuries ago, understanding physical properties of biological material, their interference with their natural host and their potential manipulation for employment as a conductor in medical devices, has gathered substantial interest in the field of bioelectronics. With the fast-emerging technologies for fabrication of diagnostic modalities, wearable biosensors and implantable devices, which electrical components are of essential importance, a need for developing novel conductors within such devices has evolved over the past decades. As the possibility of electron transport within small biological molecules, such as DNA and proteins, as well as larger elements such as cells was established, several discoveries of the modern charge characterization technologies were evolved. Development of Electrochemical Scanning Tunneling Microscopy and Nuclear Magnetic Resonance among many other techniques were of vital importance, following the discoveries made in sub-micron scales of biological material. This review covers the most recent understandings of electronic properties within different scale of biological material starting from nanometer range to millimeter-sized organs. We also discuss the state-of-the-art technology that's been made taking advantage of electronic properties of biological material for addressing diseases like Parkinson's Disease and Epilepsy.

Noise-Resistant CECG Using Novel Capacitive Electrodes

For years, capacitive electrocardiogram (CECG) has been known to be susceptible to ambient interference. In light of this, a novel capacitive electrode was developed as an effective way to reduce the interference effect. This was done by simply introducing the capacitive elector in series with a 1 pF capacitor, and the 60 Hz common mode noise induced by AC power lines was cancelled using a capacitive right leg (CRL) circuit. The proposed electrode did as expected outperform two counterparts in terms of SNR, and particularly gave an up to 99.8% correlation between RRIs extracted from an ECG and a CECG signal, a figure far beyond 52% and 63% using the two counterparts. This capacitive electrode was originally designed for long-term noncontact monitoring of heart rate, and hopefully can be integrated to portable devices for other medical care services in the near future.

A Novel Antibacterial Membrane Electrode Based on Bacterial Cellulose/Polyaniline/AgNO3 Composite for Bio-Potential Signal Monitoring

We propose a flexible, dry, and antibacterial electrode with a low and stable skin electrode contact impedance for bio-potential signal monitoring. We fabricated a bacterial cellulose/polyaniline/AgNO₃ nanocomposite membrane (BC/PANI/AgNO₃) and used it for bio-potential signal monitoring. The bacterial cellulose (BC) provides a 3-D nanoporous network structure, and it was used as a substrate material in the BC/PANI/AgNO₃ nanocomposite membrane. Polyaniline (PANI) and AgNO₃, acting as conductive and antibacterial components, respectively, were polymerized and deposited on the surfaces of BC nanofibers to produce uniform thin film membrane with flexible, antibacterial, and conductive properties. Various measurements were conducted, in terms of antibacterial activity, skin electrode contact impedance, and qualitative analysis of ECG signal recordings. The BC/PANI/AgNO3 membrane revealed 100% antibacterial activities against both the Staphylococcus aureus and Escherichia coli bacteria. The skin electrode contact impedance of the proposed BC/PANI/AgNO₃ electrode is lower than that of the Ag/AgCl gel electrode, with the same active area. In addition, the electrocardiogram (ECG) signals acquired with the proposed electrodes have stable characteristic waveforms, and they are not contaminated by noise. The waveform fidelity of the BC/PANI/AgNO₃ membrane electrodes over 800 ECG cardiac cycles is 99.49%, and after the electrodes were worn for 24 hours, a fidelity of 98.40% was recorded over the same number of cardiac cycles. With the low and stable skin electrode contact impedance, the proposed dry BC/PANI/AgNO₃ membrane electrode provided high fidelity for ECG signal recordings, thus offering a potential approach for bio-potential signal monitoring. With the above benefits, the novel flexible and dry BC/PANI/AgNO₃ electrode has a significant antibacterial. Most of all, it is the first research to develop antibacterial in the electrode design.

Noise Model of Capacitive and Textile Capacitive Noncontact Electrodes for Bioelectric Applications

In this paper, a comprehensive model for the electronic noise properties and frequency-dependent responses of printed circuit board (PCB)-based as well as textile noncontact capacitive electrodes is presented. For bioelectric diagnostics, noncontact capacitive electrodes provide an interesting alternative to classical galvanically coupled electrodes, since such a low-cost diagnostic system can be applied without preparation time and in mobile wireless environments. For even higher user comfort, textile capacitive electrodes are preferable. This paper provides a thorough study of the influence of the electrical components of capacitive electrodes and textile capacitive electrodes, as well as their surface area and circumferences on the resulting noise properties of the electrode by independently measuring the corresponding noise spectra. Consequently, the equivalent noise model is developed. The most important noise source is the high input bias resistance, which, in combination with the involved capacitance, results in an apparent $1/f^2$-power noise spectrum. By comparing the noise measurements with the noise model of the electrode, we conclude that the surface of the electrode contributes to an additional $1/f$ -power noise in the noise spectrum. We also found that the highest possible coupling capacitance is most favorable for low-noise behavior. Therefore, electrodes with electrically conducting fabric surfaces are investigated. Due to this, it is possible to enlarge the surface of the electrode and maintain a small distance between the body and the surface of the electrode. We show that with the use of textile capacitive electrodes, it is possible to reduce the noise characteristics considerably. Our findings in this paper provide a necessary source for further optimization of capacitive electrodes for bioelectric measurement applications.

Obstacles in using a computer screen for steady-state visually evoked potential stimulation

In brain computer interface (BCI) applications, the use of steady-state visually evoked potentials (SSVEPs) is common. Therefore, a visual stimulation with a constant repetition frequency is necessary. However, using a computer monitor, the set of frequencies that can be used is restricted by the refresh rate of the screen. Frequencies that are not an integer divisor of the refresh rate cannot be displayed correctly. Furthermore, the programming language the stimulation software is written in and the operating system influence the actually generated and presented frequencies. The aim of this paper is to identify the main challenges in generating SSVEP stimulation using a computer screen with and without using DirectX in Windows-based PC systems and to provide solutions for these issues.

Design and Development of Non-Contact Bio-Potential Electrodes for Pervasive Health Monitoring Applications

For the advent of pervasive bio-potential monitoring, it will be necessary to utilize a combination of cheap, quick to apply, low-noise electrodes and compact electronics with wireless technologies. Once available, all electrical activity resulting from the processes of the human body could be actively and constantly monitored without the need for cumbersome application and maintenance. This could significantly improve the early diagnosis of a range of different conditions in high-risk individuals, opening the possibility for new treatments and interventions as conditions develop. This paper presents the design and implementation of compact, non-contact capacitive bio-potential electrodes utilising a low impedance current-to-voltage configuration and a bootstrapped voltage follower, demonstrating results applicable to research applications for capacitive electrocardiography and capacitive electromyography. The presented electrodes use few components, have a small surface area and are capable of acquiring a range of bio-potential signals.

Wearable Noncontact Armband for Mobile ECG Monitoring System

One of the best ways to obtain health information is from an electrocardiogram (ECG). Through an ECG, characteristics such as patients' heartbeats, heart conditions, and heart disease can be analyzed. Unfortunately, most available healthcare devices do not provide clinical data such as information regarding patients' heart activities. Many researchers have tried to solve this problem by inventing wearable heart monitoring systems with a chest strap or wristband, but their performances were not feasible for practical applications. Thus, the aim of this study is to build a new system to monitor heart activity through ECG signals. The proposed system consists of capacitive-coupled electrodes embedded in an armband. It is considered to be a reliable, robust, and low-power-transmission ECG monitoring system. The reliability of this system was achieved by the careful placement of sensors in the armband. Bluetooth low energy (BLE) was used as the protocol for data transmission; this protocol was proposed to develop the low-power-transmission system. For robustness, the proposed system is equipped with analysis capabilities-e.g., real-time heartbeat detection and a filter algorithm to ignore distractions from body movements or noise from the environment.

Multi-Channel Capacitive Sensor Arrays

In this paper, multi-channel capacitive sensor arrays based on microstrip band-stop filters are studied. The sensor arrays can be used to detect the proximity of objects at different positions and directions. Each capacitive sensing structure in the array is connected to an inductive element to form resonance at different frequencies. The resonances are designed to be isolated in the frequency spectrum, such that the change in one channel does not affect resonances at other channels. The inductive element associated with each capacitive sensor can be surface-mounted inductors, integrated microstrip inductors or metamaterial-inspired structures. We show that by using metamaterial split-ring structures coupled to a microstrip line, the quality factor of each resonance can be greatly improved compared to conventional surface-mounted or microstrip meander inductors. With such a microstrip-coupled split-ring design, more sensing elements can be integrated in the same frequency spectrum, and the sensitivity can be greatly improved.

Ambient and Unobtrusive Cardiorespiratory Monitoring Techniques

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.

Novel active comb-shaped dry electrode for EEG measurement in hairy site

Electroencephalography (EEG) is an important biopotential, and has been widely applied in clinical applications. The conventional EEG electrode with conductive gels is usually used for measuring EEG. However, the use of conductive gel also encounters with the issue of drying and hardening. Recently, many dry EEG electrodes based on different conductive materials and techniques were proposed to solve the previous issue. However, measuring EEG in the hairy site is still a difficult challenge. In this study, a novel active comb-shaped dry electrode was proposed to measure EEG in hairy site. Different form other comb-shaped or spike-shaped dry electrodes, it can provide more excellent performance of avoiding the signal attenuation, phase distortion, and the reduction of common mode rejection ratio. Even under walking motion, it can effectively acquire EEG in hairy site. Finally, the experiments for alpha rhythm and steady-state visually evoked potential were also tested to validate the proposed electrode.

Flexible capacitive electrodes for minimizing motion artifacts in ambulatory electrocardiograms

This study proposes the use of flexible capacitive electrodes for reducing motion artifacts in a wearable electrocardiogram (ECG) device. The capacitive electrodes have conductive foam on their surface, a shield, an optimal input bias resistor, and guarding feedback. The electrodes are integrated in a chest belt, and the acquired signals are transmitted wirelessly for ambulatory heart rate monitoring. We experimentally validated the electrode performance with subjects standing and walking on a treadmill at speeds of up to 7 km/h. The results confirmed the highly accurate heart rate detection capacity of the developed system and its feasibility for daily-life ECG monitoring.

Unobtrusive ECG monitoring in the NICU using a capacitive sensing array

The thin skin of preterm babies is easily damaged by adhesive electrodes, tapes, chest drains and needle-marks. The scars caused could be disfiguring or disabling to 10% of preterm newborns. Capacitive sensors present an attractive option for pervasively monitoring neonatal ECG, and can be embedded in a support system or even a garment worn by the neonate. This could improve comfort and reduce pain aiding better recovery as well as avoiding the scars caused by adhesive electrodes. In this work, we investigate the use of an array of capacitive sensors unobtrusively embedded in a mattress and used in a clinical environment for 15 preterm neonates. We also describe the analysis framework including the fusion of information from all sensors to provide a more accurate ECG signal. We propose a channel selection strategy as well as a method using physiological information to obtain a reliable ECG signal. When sensor coverage is well attained, results for both instantaneous heart rate and ECG signal shape analysis are very encouraging. The study also provides several insights on important factors affecting the results. These include the effect of textile type, number of layers, interferences (e.g. people walking by), motion severity and interventions. Incorporating this knowledge in the design of a capacitive sensing system would be crucial in ensuring that these sensors provide a reliable ECG signal when embedded in a neonatal support system.

IMPLEMENTATION OF MULTIPLE-CHANNEL CAPACITIVE ECG MEASUREMENT BASED ON CONDUCTIVE FABRIC

Capacitive electrocardiogram (cECG) measurement is an attractive approach for long-term health monitoring. However, there is little literature available for the implementation of multiple-channel cECG system in standard limb leads. The circuit diagram for such a system is also rarely available in literature. This paper presents a multiple-channel limb-lead cECG system that utilized conductive fabrics as the capacitive sensors. The design criteria and the corresponding circuit diagram are described in detail. The proposed system also incorporates the capacitive driven-body (CDB) circuit to reduce the common-mode power-line interference (PLI). The presented system is verified to be stable by theoretic analysis and long-term experiments. The signals acquired by the presented system are competitive with those by commercially available electrocardiogram (ECG) machines. The feasible size and distance to the subject for the sensor made by conductive fabric have also been evaluated by a series of tests. From the test results, the sensor is suggested to be of greater than 60 cm2 in area and not more than 3 mm in distance for cECG measurement.

Lower limb wearable capacitive sensing and its applications to recognizing human gaits

In this paper, we present an approach to sense human body capacitance and apply it to recognize lower limb locomotion modes. The proposed wearable sensing system includes sensing bands, a signal processing circuit and a gait event detection module. Experiments on long-term working stability, adaptability to disturbance and locomotion mode recognition are carried out to validate the effectiveness of the proposed approach. Twelve able-bodied subjects are recruited, and eleven normal gait modes are investigated. With an event-dependent linear discriminant analysis classifier and feature selection procedure, four time-domain features are used for pattern recognition and satisfactory recognition accuracies (97:3% ± 0:5%, 97:0% ± 0:4%, 95:6% ± 0:9% and 97:0% ± 0:4% for four phases of one gait cycle respectively) are obtained. The accuracies are comparable with that from electromyography-based systems and inertial-based systems. The results validate the effectiveness of the proposed lower limb capacitive sensing approach in recognizing human normal gaits.

Development of Novel Non-Contact Electrodes for Mobile Electrocardiogram Monitoring System

Real-time monitoring of cardiac health is helpful for patients with cardiovascular disease. Many telemedicine systems based on ubiquitous computing and communication techniques have been proposed for monitoring the user's electrocardiogram (ECG) anywhere and anytime. Usually, wet electrodes are used in these telemedicine systems. However, wet electrodes require conduction gels and skin preparation that can be inconvenient and uncomfortable for users. In order to overcome this issue, a new non-contact electrode circuit was proposed and applied in developing a mobile electrocardiogram monitoring system. The proposed non-contact electrode can measure bio-potentials across thin clothing, allowing it to be embedded in a user's normal clothing to monitor ECG in daily life. We attempted to simplify the design of these non-contact electrodes to reduce power consumption while continuing to provide good signal quality. The electrical specifications and the performance of monitoring arrhythmia in clinical settings were also validated to investigate the reliability of the proposed design. Experimental results show that the proposed non-contact electrode provides good signal quality for measuring ECG across thin clothes.

Design and development of an automated, portable and handheld tablet personal computer-based data acquisition system for monitoring electromyography signals during rehabilitation

This article describes the design of a robust, inexpensive, easy-to-use, small, and portable online electromyography acquisition system for monitoring electromyography signals during rehabilitation. This single-channel (one-muscle) system was connected via the universal serial bus port to a programmable Windows operating system handheld tablet personal computer for storage and analysis of the data by the end user. The raw electromyography signals were amplified in order to convert them to an observable scale. The inherent noise of 50 Hz (Malaysia) from power lines electromagnetic interference was then eliminated using a single-hybrid IC notch filter. These signals were sampled by a signal processing module and converted into 24-bit digital data. An algorithm was developed and programmed to transmit the digital data to the computer, where it was reassembled and displayed in the computer using software. Finally, the following device was furnished with the graphical user interface to display the online muscle strength streaming signal in a handheld tablet personal computer. This battery-operated system was tested on the biceps brachii muscles of 20 healthy subjects, and the results were compared to those obtained with a commercial single-channel (one-muscle) electromyography acquisition system. The results obtained using the developed device when compared to those obtained from a commercially available physiological signal monitoring system for activities involving muscle contractions were found to be comparable (the comparison of various statistical parameters) between male and female subjects. In addition, the key advantage of this developed system over the conventional desktop personal computer-based acquisition systems is its portability due to the use of a tablet personal computer in which the results are accessible graphically as well as stored in text (comma-separated value) form.

Evaluation of a novel portable capacitive ECG system in the clinical practice for a fast and simple ECG assessment in patients presenting with chest pain: FIDET (Fast Infarction Diagnosis ECG Trial)

Background

Electrocardiogram (ECG) assessment plays a crucial role in patients presenting with chest pain and suspected acute coronary syndrome (ACS). In a pilot study, we previously evaluated a capacitive ECG system (cECG) as a novel ECG technique for a fast and simple ECG assessment in patients with ST-elevation myocardial infarction (STEMI). In a next step, the sensitivity and specificity of this novel ECG technique have to be assessed in patients with ACS.

Hypothesis

The Fast Infarction Diagnosis ECG Trial (FIDET) is a prospective, bi-center, observer-blinded noninferiority study to evaluate the cECG compared to the conventional ECG (kECG) in the clinical practice for ECG assessment in consecutive patients presenting with suspected ACS.

Methods

In 250 patients who were admitted to the hospital, because of an ACS [including STEMI and non-ST-elevation acute coronary syndrome (NSTE-ACS)], both a kECG and a cECG recording were performed within a time lag of less than 10 min.

End points

The primary end point will be sensitivity and specificity of the cECG compared to the kECG in diagnosing a STEMI with a margin of noninferiority of 7.5 %. Secondary end points include sensitivity and specificity of the cECG compared to the kECG in diagnosing an NSTE-ACS, safety of the cECG system (adverse event, serious adverse event and suspected unexpected serious adverse reaction), parameters of the ECG measurement (PQ-interval, QT-interval, ST-amplitude and heart rate) and measurement duration of the two methods.

Conclusion

FIDET is designed as a noninferiority study to show that a novel cECG system is suitable for the diagnosis of myocardial infarction in the clinical context and might even have benefits, for example by offering a faster and easier ECG assessment.

Matrix of regularity for improving the quality of ECGs

The 12-lead electrocardiography (ECG) is the gold standard for diagnosis of abnormalities of the heart. However, the ECG is susceptible to artifacts, which may lead to wrong diagnosis and thus mistreatment. It is a clinical challenge of great significance differentiating ECG artifacts from patterns of diseases. We propose a computational framework, called the matrix of regularity, to evaluate the quality of ECGs. The matrix of regularity is a novel mechanism to fuse results from multiple tests of signal quality. Moreover, this method can produce a continuous grade, which can more accurately represent the quality of an ECG. When tested on a dataset from the Computing in Cardiology/PhysioNet Challenge 2011, the algorithm achieves up to 95% accuracy. The area under the receiver operating characteristic curve is 0.97. The developed framework and computer program have the potential to improve the quality of ECGs collected using conventional and portable devices.

In the Spotlight: BioInstrumentation

This review briefly introduces three topics from recent publications in this field. These are: 1) new concepts of measurement methods; 2) noteworthy improvements of existing methods; and 3) feasible applications of bioinstrumentation.

First clinical evaluation of a novel capacitive ECG system in patients with acute myocardial infarction

Objective

The ECG plays a central role in the rapid diagnosis of acute myocardial infarctions (MI). In haemodynamically instable patients, adhesion of electrodes sometimes is difficult and assessing ECGs through layers of clothes has not been done so far. A novel capacitive measurement of ECG signals is possible without skin contact. Whether this technical innovation can be used in patients with MI is unclear.

Methods

We evaluated a capacitive ECG system (cECG) in patients with anterior and inferior ST elevation MI (STEMI) as compared to patients without ST elevations in anterior and inferior leads. The cECG was assessed using a sensor array consisting of 15 electrodes of which the classical leads I, II, III, aVL, aVF and V₁–V₃ were calculated from. 66 patients were included in the study. In addition to the conventional ECG (kECG) the novel cECG was registered before reperfusion therapy was started.

Results

In a first round, 19 patients presented with anterior MI, 23 with inferior MI, and 7 either with left bundle branch block or lateral MI. Regarding anterior MI, a significant correlation (P < 0.05) was found between ST elevations in leads I, aVL, V₂ and V₃ comparing cECG and kECG. In inferior MI, there was only a significant correlation (P < 0.05) in lead III between cECG and kECG, but not in II and aVF. Therefore, 17 additional patients were included in the study by placing an additional electrode further away from the sensor array on the chest. ST elevations now correlated in all inferior leads II, III and aVF (P < 0.05) as measured in 9 patients with inferior MI. In addition, in 8 patients an inferior MI was correctly ruled out.

Conclusion

It is possible to identify STEMIs by cECG. This innovative technique could play an important role in the pre-hospital period as well as in the hospital.

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.

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.

Capacitive ECG system with direct access to standard leads and body surface potential mapping

Capacitive electrodes provide the same access to the human electrocardiogram (ECG) as galvanic electrodes, but without the need of direct electrical skin contact and even through layers of clothing. Thus, potential artifacts as a result of poor electrode contact to the skin are avoided and preparation time is significantly reduced. Our system integrates such capacitive electrodes in a 15 sensor array, which is combined with a Tablet PC. This integrated lightweight ECG system (cECG) is easy to place on the chest wall and allows for simultaneous recordings of 14 ECG channels, even if the patient is slightly dressed, e.g., with a t-shirt. In this paper, we present preliminary results on the performance of the cECG regarding the capability of recording body surface potential maps (BSPMs) and obtaining reconstructed standard ECG leads including Einthoven, Goldberger and, with some limitations, Wilson leads. All signals were measured having the subject lie in a supine position and wear a cotton shirt. Signal quality and diagnostic ECG information of the extracted leads are compared with standard ECG measurements. The results show a very close correlation between both types of ECG measurements. It is concluded that the cECG lends itself to rapid screening in clinically unstable patients.

Extraction of SSVEP signals of a capacitive EEG helmet for human machine interface

The use of capacitive electrodes for measuring EEG eliminates the preparation procedure known from classical noninvasive EEG measurements. The insulated interface to the brain signals in combination with steady-state visual evoked potentials (SSVEP) enables a zero prep human machine interface triggered by brain signals. This paper presents a 28-channel EEG helmet system based on our capacitive electrodes measuring and analyzing SSVEPs even through scalp hair. Correlation analysis is employed to extract the stimulation frequency of the EEG signal. The system is characterized corresponding to the available detection time with different subjects. As demonstration of the use of capacitive electrodes for SSVEP measurements, preliminary online Brain-Computer Interface (BCI) results of the system are presented. Detection times lie about a factor of 3 higher than in galvanic EEG SSVEP measurements, but are low enough to establish a proper communication channel for Human Machine Interface (HMI).