Life expectancy in most countries has been increasing continually over the several few decades thanks to significant improvements in medicine, public health, as well as personal and environmental hygiene. However, increased life expectancy combined with falling birth rates are expected to engender a large aging demographic in the near future that would impose significant burdens on the socio-economic structure of these countries. Therefore, it is essential to develop cost-effective, easy-to-use systems for the sake of elderly healthcare and well-being. Remote health monitoring, based on non-invasive and wearable sensors, actuators and modern communication and information technologies offers an efficient and cost-effective solution that allows the elderly to continue to live in their comfortable home environment instead of expensive healthcare facilities. These systems will also allow healthcare personnel to monitor important physiological signs of their patients in real time, assess health conditions and provide feedback from distant facilities. In this paper, we have presented and compared several low-cost and non-invasive health and activity monitoring systems that were reported in recent years. A survey on textile-based sensors that can potentially be used in wearable systems is also presented. Finally, compatibility of several communication technologies as well as future perspectives and research challenges in remote monitoring systems will be discussed.

Wearable Sensors for Remote Health Monitoring.

Under the alternating electrical excitation, biological tissues produce a complex electrical impedance which depends on tissue composition, structures, health status, and applied signal frequency, and hence the bioelectrical impedance methods can be utilized for noninvasive tissue characterization. As the impedance responses of these tissue parameters vary with frequencies of the applied signal, the impedance analysis conducted over a wide frequency band provides more information about the tissue interiors which help us to better understand the biological tissues anatomy, physiology, and pathology. Over past few decades, a number of impedance based noninvasive tissue characterization techniques such as bioelectrical impedance analysis (BIA), electrical impedance spectroscopy (EIS), electrical impedance plethysmography (IPG), impedance cardiography (ICG), and electrical impedance tomography (EIT) have been proposed and a lot of research works have been conducted on these methods for noninvasive tissue characterization and disease diagnosis. In this paper BIA, EIS, IPG, ICG, and EIT techniques and their applications in different fields have been reviewed and technical perspective of these impedance methods has been presented. The working principles, applications, merits, and demerits of these methods has been discussed in detail along with their other technical issues followed by present status and future trends.

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Bioelectrical Impedance Methods for Noninvasive Health Monitoring: A Review.

Brain activity associated with attention sustained on the task of safe driving has received considerable attention recently in many neurophysiological studies. Those investigations have also accurately estimated shifts in drivers' levels of arousal, fatigue, and vigilance, as evidenced by variations in their task performance, by evaluating electroencephalographic (EEG) changes. However, monitoring the neurophysiological activities of automobile drivers poses a major measurement challenge when using a laboratory-oriented biosensor technology. This work presents a novel dry EEG sensor based mobile wireless EEG system (referred to herein as Mindo) to monitor in real time a driver's vigilance status in order to link the fluctuation of driving performance with changes in brain activities. The proposed Mindo system incorporates the use of a wireless and wearable EEG device to record EEG signals from hairy regions of the driver conveniently. Additionally, the proposed system can process EEG recordings and translate them into the vigilance level. The study compares the system performance between different regression models. Moreover, the proposed system is implemented using JAVA programming language as a mobile application for online analysis. A case study involving 15 study participants assigned a 90 min sustained-attention driving task in an immersive virtual driving environment demonstrates the reliability of the proposed system. Consistent with previous studies, power spectral analysis results confirm that the EEG activities correlate well with the variations in vigilance. Furthermore, the proposed system demonstrated the feasibility of predicting the driver's vigilance in real time.

https://ir.nctu.edu.tw:443/bitstream/11536/24756/1/000337154000003.pdf

Wireless and Wearable EEG System for Evaluating Driver Vigilance

We present wearable dry electrodes made of silver nanowires for electrophysiological sensing such as electrocardiography and electromyography. The dry electrodes perform as well as the Ag/AgCl wet electrodes when the subject is resting and show fewer motion artifacts, but without the electrolytic gel. The nanowire electrodes show no signs of skin irritation, which is desirable for long-term health monitoring.

/pdf/wearable-silver-nanowire-dry-electrodes-for-2r0kgk0ycf.pdf

Wearable silver nanowire dry electrodes for electrophysiological sensing

Functionalized textiles and graphene are both emerging materials for wearable technologies. Here, we unite graphene with ordinary textiles and report the development of graphene-clad, conductive textile electrodes for biosignal acquisition specifically in cardiac monitoring. The proposed electrode was prepared by dipping nylon fabric in reduced graphene oxide (rGO) solution followed by a subsequent thermal treatment to allow conformal coating of conductive graphene layers around the fabric. The application of the electrode was demonstrated by successful measurements of the electrocardiogram (ECG). Performance of the textile-based electrodes were compared to the conventional silver/silver chloride (Ag/AgCl) electrodes in terms of skin-electrode impedance, ECG signal quality and noise levels. Excellent conformity and cross correlation of 97% was achieved between the signals measured with the new graphene-clad textile electrodes and conventional electrodes.

Graphene-clad textile electrodes for electrocardiogram monitoring

Electrode properties are key to the quality of measured biopotential signals. Ubiquitous health care systems require long-term monitoring of biopotential signals from normal volunteers and patients in home or hospital environments. In these settings it is appropriate to use dry textile electrode networks for monitoring purposes, rather than the gel or saline-sponge skin interfaces used with Ag/AgCl electrodes. In this study, we report performance test results of two different electrospun conductive nanofiber webs, and three metal plated fabrics. We evaluated contact impedance, step response, noise and signal fidelity performance indices for all five dry electrodes, and compared them to those of conventional Ag/AgCl electrodes. Overall, we found nanofiber web electrodes matched Ag/AgCl electrode performance more closely than metal plated fabric electrodes, with the contact resistance and capacitance of Ag plated PVDF nanofiber web electrodes being most similar to Ag/AgCl over the 10 Hz to 500 kHz frequency range. We also observed that step responses of all three metal-plated fabrics were poorer than those for nanofiber web electrodes and Ag/AgCl. Further, noise standard deviation and noise power spectral densities were generally lower in nanofiber web electrodes than metal plated fabrics; and waveform fidelity of ECG-like traces recorded from nanofiber web electrodes was higher than for metal plated fabrics. We recommend textile nanofiber web electrodes in applications where flexibility, comfort and durability are required in addition to good electrical characteristics.

Nanofiber Web Textile Dry Electrodes for Long-Term Biopotential Recording

Efficient connection of multiple electrodes to the body for impedance measurement and voltage monitoring applications is of critical importance to measurement quality and practicality. Electrical impedance tomography (EIT) experiments have generally required a cumbersome procedure to attach the multiple electrodes needed in EIT. Once placed, these electrodes must then maintain good contact with the skin during measurements that may last several hours. There is usually also the need to manage the wires that run between the electrodes and the EIT system. These problems become more severe as the number of electrodes increases, and may limit the practicality and portability of this imaging method. There have been several trials describing human–electrode interfaces using configurations such as electrode belts, helmets or rings. In this paper, we describe an electrode belt we developed for long-term EIT monitoring of human lung ventilation. The belt included 16 embossed electrodes that were designed to make good contact with the skin. The electrodes were fabricated using an Ag-plated PVDF nanofiber web and metallic threads. A large contact area and padding were used behind each electrode to improve subject comfort and reduce contact impedances. The electrodes were incorporated, equally spaced, into an elasticated fabric belt. We tested the electrode belt in conjunction with the KHU Mark1 multi-frequency EIT system, and demonstrate time-difference images of phantoms and human subjects during normal breathing and running. We found that the Ag-plated PVDF nanofiber web electrodes were suitable for long-term measurement because of their flexibility and durability. Moreover, the contact impedance and stability of the Ag-plated PVDF nanofiber web electrodes were found to be comparable to similarly tested Ag/AgCl electrodes.

https://iopscience.iop.org/article/10.1088/0967-3334/33/10/1603/pdf

Flexible electrode belt for EIT using nanofiber web dry electrodes

An electrical impedance tomography (EIT) system can visualize conductivity and permittivity distributions inside the human body from measured boundary voltages induced by externally injected currents. We have developed a fully parallel multi-frequency EIT system called the KHU Mark2.5. It is based on an impedance measurement module (IMM) comprising a current source, a voltmeter and a calibration circuit. Each IMM is independent and can calibrate its own current source and voltmeter through an automatic self-calibration procedure. We found that the output impedance values of all current sources are greater than 1M› at the chosen frequencies. The CMRR is around 96dB and the voltmeter SNR is between 80 and 85dB depending. To increase spatial resolution of conductivity and permittivity images, we can cascade multiple EIT systems to form a system with a larger number of channels. They are synchronized by clock synchronization circuits. Physiological events such as cardiac and respiratory functions alter electrical tissue properties. To correlate such events with EIT images, we can perform a biosignal-gated EIT imaging. We can improve interpretation of EIT images by incorporating real-time ECG and respiration signals into EIT images. This may allow us to separate fast cardiac events and slow respiratory events from reconstructed EIT images and also improve the SNR by signal-gated data averaging We present the performance of the KHU Mark2.5 system with experimental results of animal.

Tae Eui Kim

Papers

Nanofiber Web Textile Dry Electrodes for Long-Term Biopotential Recording

Flexible electrode belt for EIT using nanofiber web dry electrodes

Expandable Multi-frequency EIT System for Clinical Applications