Electrode-skin Interface Impedance Research Articles

A 0.67 μV-IIRN super-T Ω-Z IN 17.5 μW/Ch Active Electrode With In-Channel Boosted CMRR for Distributed EEG Monitoring.

We present the design, development, and experimental characterization of an active electrode (AE) IC for wearable ambulatory EEG recording. The proposed architecture features in-AE double common-mode (CM) rejection, making the recording's CMRR independent of typically-significant AE-to-AE gain variations. Thanks to being DC coupled and needless of chopper stabilization for flicker noise suppression, the architecture yields a super-T Ω input impedance. Such a large input impedance makes the AE's CMRR practically immune to electrode-skin interface impedance variations across different recording channels, a critical feature for dry-electrode ambulatory systems. Signal quantization and serialization are also performed in-AE, which enables a distributed system in which all AEs use a single data bus for data/command communication to the backend module, thus significantly improving the system's scalability. Additionally, the presented AE hosts auxiliary modules for (i) detection of an unstable electrode-skin connection through continuous interface impedance monitoring, (ii) dynamic measurement and adjustment of input DC level, and (iii) a CM feedback loop for further CMRR enhancement. The article also presents the development of printed (extrusion) tattoo electrodes and their experimental characterization results with the proposed AE architecture. Besides bio-compatibility, low-cost, pattern flexibility, and quick fabrication process, the printed electrodes offer a very stable electrode-skin connection, conform to scalp shape, and exhibit consistent performance under various bending curvatures. Analog circuit blocks of the presented AE architecture are designed and fabricated using a standard 180 nm CMOS technology, and the [Formula: see text] IC is integrated with off-chip low-power digital modules on a PCB to form the AE. Our measurement results show a CMRR of 82.2 dB (at 60 Hz), amplification voltage gain of 52.8 dB, a bandwidth of 0.2-400 Hz, ±500 mV input DC offset tolerance, An input impedance [Formula: see text], and 0.67 μV RMS integrated input referred noise (0.5-100 Hz), while consuming 17.5 μW per channel. All auxiliary modules are tested experimentally, and the entire system is validated in-vivo, for both ECG and EEG recording.

Microneedle Array Electrodes Fabricated With 3D Printing Technology for High-Quality Electrophysiological Acquisition.

Electrophysiological recordings are vital in assessing biological functions, diagnosing diseases, and facilitating biofeedback and rehabilitation. The applications of conventional wet (gel) electrodes often come with some limitations. Microneedle array electrodes (MAEs) present a possible solution for high-quality electrophysiological acquisition, while the prior technologies for MAE fabrication have been either complex, expensive, or incapable of producing microneedles with uniform dimensions. This work employed a projection stereolithography (P μ SL) 3D printing technology to fabricate MAEs with micrometer-level precision. The MAEs were compared with gel and flat electrodes on electrode-skin interface impedance (EII) and performances of EMG and ECG acquisition. The experimental results indicate that the P μ SL 3D printing technology contributed to an easy-to-perform and low-cost fabrication approach for MAEs. The developed MAEs exhibited promising EII and enabled a stable EMG and ECG acquisition in different conditions without inducing skin allergies, inflammation, or injuries. This research lies in the development of a type of customizable MAE with considerable biomedical application potentials for ultra-minimally invasive or non-invasive electrophysiological acquisition.

Long-Term Electrode-Skin Impedance Variation for Electromyographic Measurements.

This study aims to observe the evolution of the electrode-skin interface impedance of surface EMG electrodes over the time taken to determine the time of stabilization. Eight healthy subjects participated in the study. Electrode-skin impedance was evaluated in the rectus abdominal muscle every five minutes, over a total period of 50 min. A reduction of 13.23% in the impedance values was observed in minute 10 (p = 0.007), and a reduction of 9.02% was observed in minute 15 (p = 0.029). No statistically significant differences were observed in the other instants evaluated. The findings obtained in the present study demonstrate a decrease in electrode-skin impedance from minute 5 to minute 15, followed by a stabilization period with a low percentage of variation till minute 50.

Using microneedle array electrodes for non-invasive electrophysiological signal acquisition and sensory feedback evoking.

Introduction: Bidirectional transmission of information is needed to realize a closed-loop human-machine interaction (HMI), where electrophysiological signals are recorded for man-machine control and electrical stimulations are used for machine-man feedback. As a neural interface (NI) connecting man and machine, electrodes play an important role in HMI and their characteristics are critical for information transmission. Methods: In this work, we fabricated a kind of microneedle array electrodes (MAEs) by using a magnetization-induced self-assembly method, where microneedles with a length of 500-600μm and a tip diameter of ∼20μm were constructed on flexible substrates. Part of the needle length could penetrate through the subjects' stratum corneum and reach the epidermis, but not touch the dermis, establishing a safe and direct communication pathway between external electrical circuit and internal peripheral nervous system. Results: The MAEs showed significantly lower and more stable electrode-skin interface impedance than the metal-based flat array electrodes (FAEs) in various testing scenarios, demonstrating their promising impedance characteristics. With the stable microneedle structure, MAEs exhibited an average SNR of EMG that is more than 30% higher than FAEs, and a motion-intention classification accuracy that is 10% higher than FAEs. The successful sensation evoking demonstrated the feasibility of the MAE-based electrical stimulation for sensory feedback, where a variety of natural and intuitive feelings were generated in the subjects and thereafter objectively verified through EEG analysis. Discussion: This work confirms the application potential of MAEs working as an effective NI, in both electrophysiological recording and electrical stimulation, which may provide a technique support for the development of HMI.

(Digital Presentation) A Low-Modulus, Soft and Stretchable Wearable Electrocardiography Sensor-System Patch

Electrocardiography (ECG) is a primary tool for diagnosis of various types of disease and disorders such as arrhythmias, coronary heart disease, heart attack, mental disorders, etc. Reliable wearable ECG devices can be a valuable tool in early diagnosis and effective treatment of such disease and disorders. Convention wearable ECG sensor-systems are rigid, bulky, expensive, and the recorded ECG signals using these wearable devices lack required accuracy for medical diagnosis mainly due to motion artifacts that is originated from slippage of sensors on skin and/or instable interface between the soft sensor and the rigid electronic circuits.Here, we report a low-modulus, soft and stretchable wearable electrocardiography (ECG) sensor-system patch which enables continuous and long-term recording of ECG signals with minimal motion artifacts. This system consists of two reusable, detachable-attachable patches: sensor patch and circuit patch, as shown in Figure 1a. The reusable multi-wall carbon nanotube (MWCNT) based sensor patch is fabricated on stretchable elastomer substrate by our developed cost and time-effective method. Reusable, front-end and wireless circuit patch is made by integration of the off-the-shelf integrated circuit components with three-dimensional (3D) stretchable-deformable interconnects (SDI). SDIs are 3D springs of liquid metal (EGaIn). Unlike other reported liquid metal based interconnects, SDI has been designed in 3D form to increase the stretchability and make it low-modulus and robust to deformations in all directions. The stretchability of SDI structure is beyond 500% (the limit of our measurement system) without any negligible change in electrical resistivity of the interconnects. With less than 1% change in the resistance of SDIs after 50,000 cycles of applied tensile strain of 200%, the SDI structure ensures reliable stretchability and durability of the circuit patch for long-term electrocardiography.The sensor patch is soft, stretchable and it is fabricated using a low-cost scalable method. This soft and stretchable ECG sensor-system shows comparable performance with respect to medical grade Ag/AgCl wet gel electrodes. Our CNT-PDMS sensors shows low electrode-skin interface impedance and low susceptibility to motion artifact which similar of it in medical grade Ag/AgCl wet gel sensors (Fig. 1b). Further, it is waterproof, reusable and comfortable to wear.The circuit patch includes a rechargeable battery and ECG signals is wirelessly sent to a personal device such as cellphone, tablet and laptop through Bluetooth low energy (BLE) and it is displayed in real-time (Fig. 1c) Our developed sensor-system is a multi-use platform which can be applied for the detection of EMG, EEG or EOG signals. Figure 1

A PDMS-based microneedle array electrode for long-term ECG recording.

To acquire high-quality electrocardiogram (ECG) signals, traditional Ag/AgCl wet electrodes used together with conductive gel can effectively reduce electrode-skin interface impedance (EII) in a short term. However, their weaknesses of poor flexibility and instability can no longer meet the long-term monitoring requirements of intelligent wearable devices. Owing to the flexible dry electrode without conductive gel, it is a good choice to solve the critical problem on drying-out of conductive gel. Therefore, we develop a flexible microneedle array electrode (FMAE) based on polydimethylsiloxane (PDMS) substrate, which obtains reliable bioelectrical signals by way of penetrating into the stratum corneum (SC) of the skin. The fabrication process, including silicon mold, twice PDMS shape-transferring and encapsulation, has advantages of low cost, repeatable production and good biocompatibility. Afterwards, by comparing the performance with different electrodes, impedance test results indicate that the impedance of FMAE are smaller and more stable, and ECG tests in long term and at resting/jogging states also verify that FMAE can obtain durable, stable and reliable signals. In conclusion, FMAE is promising in long-term ECG monitoring.

High-Performance Flexible Microneedle Array as a Low-Impedance Surface Biopotential Dry Electrode for Wearable Electrophysiological Recording and Polysomnography

Highlights Polyimide-based flexible microneedle array (PI-MNA) electrodes realize high electrical/mechanical performance and are compatible with wearable wireless recording systems.The normalized electrode–skin interface impedance (EII) of the PI-MNA electrodes reaches 0.98 kΩ cm2 at 1 kHz and 1.50 kΩ cm2 at 10 Hz, approximately 1/250 of clinical standard electrodes.This is the first report on the clinical study of microneedle electrodes. The PI-MNA electrodes are applied to clinical long-term continuous monitoring for polysomnography.Microneedle array (MNA) electrodes are an effective solution to achieve high-quality surface biopotential recording without the coordination of conductive gel and are thus very suitable for long-term wearable applications. Existing schemes are limited by flexibility, biosafety, and manufacturing costs, which create large barriers for wider applications. Here, we present a novel flexible MNA electrode that can simultaneously achieve flexibility of the substrate to fit a curved body surface, robustness of microneedles to penetrate the skin without fracture, and a simplified process to allow mass production. The compatibility with wearable wireless systems and the short preparation time of the electrodes significantly improves the comfort and convenience of electrophysiological recording. The normalized electrode–skin contact impedance reaches 0.98 kΩ cm2 at 1 kHz and 1.50 kΩ cm2 at 10 Hz, a record low value compared to previous reports and approximately 1/250 of the standard electrodes. The morphology, biosafety, and electrical/mechanical properties are fully characterized, and wearable recordings with a high signal-to-noise ratio and low motion artifacts are realized. The first reported clinical study of microneedle electrodes for surface electrophysiological monitoring was conducted in tens of healthy and sleep-disordered subjects with 44 nights of recording (over 8 h per night), providing substantial evidence that the electrodes can be leveraged to substitute for clinical standard electrodes.

Substrate-free, ultra-conformable PEDOT: PSS E-tattoo achieved by energy regulation on skin

Electronic tattoo has great potential application in mobile health. Fully conformal contact between E-tattoo and skin is critical for reliable monitoring. In this paper, we reported a substrate-free, ultra-conformable PEDOT: PSS (3,4-ethylenedioxythiophene):poly(styrene-sulfonate) E-tattoo achieved by interface energy regulation on skin. The controllable gel/dry electrode mutual transformation property of PEDOT: PSS was carefully studied and reported. Then a novel transfer approach was studied to transfer thin, substrate-free PEDOT: PSS E-tattoo onto skin. Meanwhile, PEDOT: PSS E-tattoo was gelled, then dried directly on skin, regulating its bending energy, contact area, and interface adhesion energy with skin. Through this method, the critical thickness of the after-transformation dry E-tattoo that could form fully conformal contact with skin was increased by 4 times. The electrode-skin interface impedance and ECG measurement performance of the reported E-tattoo were on par with commercial Ag/AgCl gel electrodes, while offering superior comfort and reliability. The substrate-free, ultra-conformable PEDOT: PSS E-tattoo could be applied as sensing electrode for reliable monitoring in mobile health.

Fabrication of Bendable Microneedle-Array Electrode by Magnetorheological Drawing Lithography for Electroencephalogram Recording

Continuous electroencephalogram (EEG) recording is vital for brain science research, monitoring pathological and physiological conditions, and the diagnosis of brain disease. Conventional wet electrodes require skin preparation and a gel electrolyte to reduce electrode–skin interface impedance (EII), which limits its further application in long-term EEG signal recording. Microneedle-array electrodes (MAEs) have been employed in EEG recording, as they can be used directly without skin preparation or the gel electrolyte. However, most microneedles used in MAE are rigid and have a high aspect ratio; thus, they can break easily. Hence, we developed a novel bendable MAE for EEG recording. It is made of a flexible polydimethylsiloxane (PDMS) pillar array with rigid microneedle tips. The PDMS pillar array could help the MAE pass through hair and enable the microneedle tips to penetrate a stratum corneum layer into a scalp, thus reducing the EII. Moreover, the PDMS pillar array is bendable, which prevents the microneedles tips from breaking. The MAE can record EEG signals well in a BIOPAC system and an Emotiv EPOC+ device. The bendable MAE may be an alternative electrode for long-term EEG recording.

A silver/silver chloride woven electrode with convex based on electrical impedance tomography

Advanced wearable medical devices are widely used for health monitoring, i.e. recording and analyzing signals from human organs. However, the signal quality is influenced significantly by medical electrodes, which became the bottleneck for health monitoring due to unstable impedance under long-term daily usage. Here, a novel monitoring electrode was designed with uniform micro-convex shape to increase the impedance reliability of electrode-skin interface in long-term monitoring and under dynamic conditions, and we set up the electrode-skin interface model to describe the electrode-skin interface and impedance distribution clearly. Furthermore, we investigated how the electrodeposition factors affect the electrode deposition uniformity and electrode resistance. In this study, we compared the monitoring performance among two sets of electrodes: 1) Ag electrodes and Ag/AgCl electrodes, 2) plain Ag/AgCl electrodes, jacquard Ag/AgCl electrodes, and commercial wet electrodes. Specifically, the monitoring performance was quantified by the electrode-skin interface impedance during long-term monitoring, under different dynamic conditions. The optimal electrodeposition process was a ‘small step’ multi-potential method with the 1-1.5-2 V mode. The jacquard Ag/AgCl electrodes presented the best monitoring performance under all three measurement scenarios across four types of electrodes. The results indicated that the proposed electrodes could be used for long-term medical monitoring under daily life activities based on electrical impedance tomography.

A Mini Review of Microneedle Array Electrode for Bio-Signal Recording: A Review

Bio-signal recording is vital for human condition monitoring and early disease diagnosis. An electrode is a biosensor for bio-signal collection. The conventional wet electrode is not suitable for long-term bio-signal recording owing to the gradual drying of the electrolytic gel and increase in the electrode-skin interface impedance. Microneedle array electrode is a dry electrode that can painlessly pierce skin, form a contact interface between the microneedles and skin tissue, eliminate the high impedance of stratum corneum, weaken the motion artifact, and accurately record bio-signals without skin preparation and application of electrolytic gel. This review focuses on the recently developed fabrication techniques, the mechanical performance, and bio-signal recording performance of microneedle array electrode. The microneedle array electrode is a potential electrode for long-term bio-signal recording, although progress is required in terms of safety and scaled-up manufacture.

(Invited) Imperceptible Graphene Based Electronic Tattoo Sensors

During last decade, there have been advances in wearables with applications in mobile healthcare, athletic, assistive technology, human machine interface and internet of things. However, current wearable sensors and systems have at least one or more of the following drawbacks: they are bulky, expensive, distractive, unsuitable for long term measurement or prone to motion artifact. We present ultrathin graphene based electronic tattoo (GET) sensors with the overall thickness of less than 500 nm. Presented e-tattoo sensors can be laminated on skin like as temporary tattoo and form conformal contact to microscopic texture of the skin. GET is a set of dry sensors with electrode-skin interface impedance comparable to wet gel electrodes that are gold standard in medical applications. Low electrode-skin interface impedance of these e-tattoo sensors results in high signal to noise ratio and high sensing quality. Due to low areal mass density of GET, it attaches to skin without any adhesive or tape, just by Van der Waals force. Presented e-tattoos are both optically and mechanically imperceptible, therefore, they are desirable for applications in prominent areas of appearance such as face. We present the successful demonstration of GET applications for electrocardiography (EEG), electroencephalography (EEG), electromyography (EMG), electrooculography (EOG), skin temperature sensing, skin hydration sensing and human robot interface.

Fabrication of Flexible Microneedle Array Electrodes for Wearable Bio-Signal Recording.

Laser-direct writing (LDW) and magneto-rheological drawing lithography (MRDL) have been proposed for the fabrication of a flexible microneedle array electrode (MAE) for wearable bio-signal monitoring. Conductive patterns were directly written onto the flexible polyethylene terephthalate (PET) substrate by LDW. The microneedle array was rapidly drawn and formed from the droplets of curable magnetorheological fluid with the assistance of an external magnetic field by MRDL. A flexible MAE can maintain a stable contact interface with curved human skin due to the flexibility of the PET substrate. Compared with Ag/AgCl electrodes and flexible dry electrodes (FDE), the electrode–skin interface impedance of flexible MAE was the minimum even after a 50-cycle bending test. Flexible MAE can record electromyography (EMG), electroencephalography (EEG) and static electrocardiography (ECG) signals with good fidelity. The main features of the dynamic ECG signal recorded by flexible MAE are the most distinguishable with the least moving artifacts. Flexible MAE is an attractive candidate electrode for wearable bio-signal monitoring.

Flexible microneedle array electrode using magnetorheological drawing lithography for bio-signal monitoring

Monitoring and timely intervention are extremely important in the continuous home care. Microneedle array electrode (MAE) have been employed for the long-term bio-signal monitoring without skin preparation. We developed a novel magneto-rheological drawing lithography (MRDL) method to cost-effectively fabricate a flexible micro-needle array electrode (FMAE) for the wearable bio-signal monitoring. Flexible substrate may match closely with curved skin and maintain a stable interface between skin and electrode. The formation mechanism of microneedle array (MA) by MRDL and bio-signal recording performance of FMAE were investigated. MA can be one-step drawn from the droplet array of curable magnetorheological fluid under the assist of external magnetic field. Ti/Au film was coated on the surface of solidified MA to insure the conductivity and compatibility of FMAE. 36-FMAE consists of 6×6 micro-needles with an average height of 600μm and an average tip radius of 12μm. FMAE with 36 needles (36-FMAE) shows a better bio-signal monitoring performance in some specific situations compared with flexible dry electrode (FDE) and commercial Ag/AgCl electrode. Electrode-skin interface impedance (EII) measured by 36-FMAE is the lowest at a given low input frequency and the amplitude of electrocardiography (ECG) and electroencephalography (EEG) signals recorded by 36-FMAE is the largest. 36-FMAE can collect more distinguishable features and weaken the effect of motion artifact during the dynamical ECG recording. Therefore, 36-FMAE is a promising sensor for the wearable bio-signal monitoring in home care.

Fabrication of Micro-Needle Electrodes for Bio-Signal Recording by a Magnetization-Induced Self-Assembly Method.

Micro-needle electrodes (MEs) have attracted more and more attention for monitoring physiological electrical signals, including electrode-skin interface impedance (EII), electromyography (EMG) and electrocardiography (ECG) recording. A magnetization-induced self-assembling method (MSM) was developed to fabricate a microneedle array (MA). A MA coated with Ti/Au film was assembled as a ME. The fracture and insertion properties of ME were tested by experiments. The bio-signal recording performance of the ME was measured and compared with a typical commercial wet electrode (Ag/AgCl electrode). The results show that the MA self-assembled from the magnetic droplet array under the sum of gravitational surface tension and magnetic potential energies. The ME had good toughness and could easily pierce rabbit skin without being broken or buckling. When the compression force applied on the ME was larger than 2 N, ME could stably record EII, which was a lower value than that measured by Ag/AgCl electrodes. EMG signals collected by ME varied along with the contraction of biceps brachii muscle. ME could record static ECG signals with a larger amplitude and dynamic ECG signals with more distinguishable features in comparison with a Ag/AgCl electrode, therefore, ME is an alternative electrode for bio-signal monitoring in some specific situations.

Fabrication of a Micro-Needle Array Electrode by Thermal Drawing for Bio-Signals Monitoring.

A novel micro-needle array electrode (MAE) fabricated by thermal drawing and coated with Ti/Au film was proposed for bio-signals monitoring. A simple and effective setup was employed to form glassy-state poly (lactic-co-glycolic acid) (PLGA) into a micro-needle array (MA) by the thermal drawing method. The MA was composed of 6 × 6 micro-needles with an average height of about 500 μm. Electrode-skin interface impedance (EII) was recorded as the insertion force was applied on the MAE. The insertion process of the MAE was also simulated by the finite element method. Results showed that MAE could insert into skin with a relatively low compression force and maintain stable contact impedance between the MAE and skin. Bio-signals, including electromyography (EMG), electrocardiography (ECG), and electroencephalograph (EEG) were also collected. Test results showed that the MAE could record EMG, ECG, and EEG signals with good fidelity in shape and amplitude in comparison with the commercial Ag/AgCl electrodes, which proves that MAE is an alternative electrode for bio-signals monitoring.

Effect of pressure and padding on motion artifact of textile electrodes.

BackgroundWith the aging population and rising healthcare costs, wearable monitoring is gaining importance. The motion artifact affecting dry electrodes is one of the main challenges preventing the widespread use of wearable monitoring systems. In this paper we investigate the motion artifact and ways of making a textile electrode more resilient against motion artifact. Our aim is to study the effects of the pressure exerted onto the electrode, and the effects of inserting padding between the applied pressure and the electrode.MethodWe measure real time electrode-skin interface impedance, ECG from two channels, the motion artifact related surface potential, and exerted pressure during controlled motion by a measurement setup designed to estimate the relation of motion artifact to the signals. We use different foam padding materials with various mechanical properties and apply electrode pressures between 5 and 25 mmHg to understand their effect. A QRS and noise detection algorithm based on a modified Pan-Tompkins QRS detection algorithm estimates the electrode behaviour in respect to the motion artifact from two channels; one dominated by the motion artifact and one containing both the motion artifact and the ECG. This procedure enables us to quantify a given setup’s susceptibility to the motion artifact.ResultsPressure is found to strongly affect signal quality as is the use of padding. In general, the paddings reduce the motion artifact. However the shape and frequency components of the motion artifact vary for different paddings, and their material and physical properties. Electrode impedance at 100 kHz correlates in some cases with the motion artifact but it is not a good predictor of the motion artifact.ConclusionFrom the results of this study, guidelines for improving electrode design regarding padding and pressure can be formulated as paddings are a necessary part of the system for reducing the motion artifact, and further, their effect maximises between 15 mmHg and 20 mmHg of exerted pressure. In addition, we present new methods for evaluating electrode sensitivity to motion, utilizing the detection of noise peaks that fall into the same frequency band as R-peaks.

Power-efficient wireless sensor for physiological signal acquisition

This work presents a power-efficient wireless sensor implemented using microelectromechanical system (MEMS)-based dry electrodes (MDE) and a ZigBee protocol chip for physiological signal acquisition. To improve signal quality with low electrode-skin interface impedance, a silicon-based MDE is fabricated via micromachining technology. The proposed wireless sensor can provide four different channels for up to 10 kHz bandwidth, 10-bit resolution biomedical signal transmissions. Different from other systems, the proposed wireless sensor employs a novel power management method for physiological signals to reduce power consumption. The proposed wireless sensor successfully transmits electrocardiogram (ECG) signals and four-channel electroencephalogram (EEG) signals with power consumptions of 92.7 and 56.8 mW respectively. It consumes 46% less power than the original sensor without power management (173 mW) in ECG acquisition and 67% less power in EEG acquisition. The circuit printed-circuit-band area in the proposed wireless sensor is 3.5×4.5 cm, suitable for various portable biomedical applications.

Factors affecting the stimulus artifact tail in surface-recorded somatosensory-evoked potentials

Surface-recorded somatosensory-evoked potentials (SEPs) are neural signals elicited by an external stimulus. In the case of electrically induced SEPs, the artifact generated by the stimulation process can severely distort the signal. In some cases, the artifact tail often lasts well into the initiation of the SEP making the determination of absolute latency very difficult. In this work, a new approach was taken to identify factors that affect the tail of the artifact. The methodology adopted was the development of a lumped electrical circuit model of the artifact generation process. While the modeling of the instrumentation hardware is relatively simple, this is not the case with tissue and electrode/skin interface effects. Consequently, this paper describes a novel tissue modeling approach that uses an autoregressive moving average (ARMA) parametric technique and an artificial neural network (ANN) to estimate tissue parameters from experimental data. This coupled with an estimation of the stimulation electrode-skin impedance completes the lumped circuit model. Simulink (The Mathworks Inc.) was used to evaluate the model under several different conditions. These results show that both the stimulation electrode-skin interface impedance and nature of the body tissue directly under the recording electrodes have a profound effect on the appearance of the stimulus artifact tail. This was verified by experimentally recorded data obtained from the median nerve using surface electrodes. Conclusions drawn from this work include that stimulation electrodes with low series capacitance should be used whenever possible to minimize the duration of the artifact tail.

Electrogastrography: a noninvasive technique to evaluate gastric electrical activity.

Electrogastrography (EGG) is the recording of gastric electrical activity (GEA) from the body surface. The cutaneous signal is low in amplitude and consequently must be amplified considerably. The resultant signal is heavily contaminated with noise, and visual analysis alone of an EGG signal is inadequate. Consequently, EGG recordings require special methodology for acquisition, processing and analysis. Essential components of this methodology involve an adequate system of digital filtering, amplification and analysis, along with minimization of the sources of external noise (random motions of the patient, electrode-skin interface impedance, electrode bending, obesity, etc) and a quantitative interpretation of the recordings. There is a close relationship between GEA and gastric motility. Although it has been demonstrated that EGG satisfactorily reflects internal GEA frequency, there is not acceptable correlation with gastric contractions or gastric emptying. Many attempts have been made to relate EGG 'abnormalities' with clinical syndromes and diseases; however, the diagnostic and clinical value of EGG is still very much in question.