Continuous Impedance Measurement Research Articles

Validation of Multi-Frequency Inductive-Loop Measurement System for Parameters of Moving Vehicle Based on Laboratory Model

The paper presents research on a system for measuring the parameters of a vehicle in motion and the process of validating it under laboratory conditions. The measurement system uses four inductive-loop (IL) sensors, two slim ILs and two wide ILs. The vehicle speed, wheelbase, length, and overhangs are all determined on the basis of a vehicle magnetic profile (VMP) waveform. VMPs are captured from the continuous IL-based impedance measurement. The impedance measurement for a single IL is performed simultaneously at three carrier frequencies. The uncontrolled measurement conditions in the field on a real road test bed (RTB), including the speed of passing vehicles, motivated the development of a laboratory test bed (LTB). This LTB serves as a model of an existing measurement setup installed on the road, i.e., the RTB. The LTB includes IL sensors and a movable model of the vehicle made in 1:50 scale. The LTB enables validation of the whole measurement system in the vehicle speed range from 10 km/h up to 150 km/h in 5 km/h increments in fully controlled conditions. The measurement results are presented in the distance domain, calculated from the VMPs and the measured speed. The largest errors in estimating vehicle-model body parameters, on a natural scale, do not exceed 4.3 cm.

Intraindividual variability of the Eustachian tube function: a longitudinal study in a pressure chamber.

The Eustachian tube (ET) is essential for fast and direct pressure equalisation between middle ear and ambient pressure. It is not yet known to what extent Eustachian tube function in healthy adults changes in a weekly periodicity due to internal and external factors. This question is particularly interesting with regard to scuba divers among whom there is a need to evaluate intraindividual ET function variability. Continuous impedance measurement in a pressure chamber was performed three times at one-week intervals between measurements. Twenty healthy participants (40 ears) were enrolled. Using a monoplace hyperbaric chamber, individual subjects were exposed to a standardised pressure profile consisting of a 20 kPa decompression over 1 min, a 40 kPa compression over 2 min, and a 20 kPa decompression over 1 min. Measurements of Eustachian tube opening pressure (ETOP), opening duration (ETOD), and opening frequency (ETOF) were made. Intraindividual variability was assessed. Mean ETOD during compression (actively induced pressure equalisation) on the right side was 273.8 (SD 158.8) ms, 259.4 (157.7) ms, and 249.2 (154.1) ms (Chi-square 7.30, P = 0.026) across weeks 1-3. Mean ETOD for both sides was 265.6 (153.3) ms, 256.1 (154.6) ms, and 245.7 (147.8) ms (Chi-square 10.00, P = 0.007) across weeks 1-3. There were no other significant differences in ETOD, ETOP and ETOF across the three weekly measurements. This longitudinal study suggests low week-to-week intraindividual variability of Eustachian tube function.

Polynomial analysis as a new way of describing dynamic impedance spectra – Differential and relative impedance spectra

Model measurements of an equivalent electrical system were carried out using the technique of Dynamic Electrochemical Impedance Spectroscopy. The measurement took the form of potentiodynamic changes imposed on the tested system. Using the possibility of continuous impedance measurements, an attempt was made to develop an original and innovative method of analyzing impedance spectrograms, which is termed polynomial analysis. As a result of this approach, it is possible to generate two novel impedance spectra from the primary impedance spectrogram. The innovation lies in the use of simple polynomials to describe a set of spectra, and then performing differential and division operations, which result in differential- and relative-impedance spectra. Among other things, differential spectra have the ability to track the rate of change in impedance as a function of an independent variable. By contrast, relative impedance spectra eliminate surface influence, which opens the way to the direct comparison of physicochemical processes and more.

A Method for Monitoring State-of-Charge of Lithium-Ion Cells Using Multi-Sine Signal Excitation

In this paper, a method for monitoring SoC of a lithium-ion battery cell through continuous impedance measurement during cell operation is introduced. A multi-sine signal is applied to the cell operating current, and the cell SoH and SoC can be simultaneously monitored via impedance at each frequency. Unlike existing studies in which cell impedance measurement is performed ex situ through EIS equipment, cell state estimation is performed in situ. The measured impedance takes into account cell temperature and cell SoH, enabling accurate SoC estimation. The measurement system configured for the experiment and considerations for the selection of measurement parameters are described, and the accuracy of cell SoC estimation is presented.

Short-Time Impedance Spectroscopy Using a Mode-Switching Nonsinusoidal Oscillator: Applicability to Biological Tissues and Continuous Measurement.

Herein, we propose an impedance spectroscopy method using a mode-switching nonsinusoidal oscillator and apply this method for measuring the impedance of biological tissues and continuous impedance measurement. To obtain impedance spectra over a wide frequency range, we fabricated a novel nonsinusoidal oscillator incorporating binary counters and analog switches. This oscillator could periodically switch oscillation frequency through the mode switching of the feedback resistor. From the oscillation waveform at each oscillation frequency of this circuit (oscillator), we determined the impedance spectrum of a measured object using the discrete-time Fourier transform. Subsequently, we obtained the broad impedance spectrum of the measured object by merging odd-order harmonic spectral components up to the 19th order for each oscillation frequency. From the measured spectrum, the resistive and capacitive components of the circuit simulating bioimpedance were estimated with high accuracy. Moreover, the proposed method was used to measure the impedance of porcine myocardium; changes in the impedance spectrum of the myocardial tissue due to coagulation could be measured. Furthermore, rapid variations in the resistance value of a CdS photocell could be continuously measured using the proposed method.

Use of Continuous Electrical Impedance Measurement for Accurate Nerve Block in Rabbits.

To perform an effective and safe nerve block, the needle must be placed near the target nerve while avoiding nerve damage. Our objective was to conduct an animal study to determine whether changes in electrical impedance (EI) could be used to guide the needle and achieve a safe and accurate nerve block. We measured the EI of rabbit tissues during ultrasound-guided sciatic nerve block using a bipolar needle via the in-plane needle approach. The EI values and needle track on the ultrasound monitor were video-recorded. When there was a change in the EI, the needle advancement was stopped, and a stained anesthetic was injected. Subsequently, the animals were euthanized, and the anesthetic-stained tissue was examined via dissection, while the other tissue was preserved at -80°C for microscopic analysis. The EI remained stable as the needle advanced through the muscle (extraneural); however, it markedly decreased when the needle tip contacted the nerve or slightly punctured the epineurium (paraneural). The mean extra- and paraneural EIs were 4.92 ± 1.31 kΩ (range, 2.39-9.67 kΩ) and 2.86 ± 0.96 kΩ (range, 1.66-5.13 kΩ), respectively. Examination of the dissections and cryostat sections showed anesthetic delivery around the nerve. EI values differed between extra- and paraneural sites, and monitoring these values allowed prediction of the needle tip location with respect to the target nerve. Real-time EI measurement could improve the nerve block.

Continuous body impedance measurement to detect bladder volume changes during urodynamic study: A prospective study in pediatric patients.

To assess the possibility of the body impedance (BI) reflecting bladder volumes (BV) in pediatric patients, the BI signals are measured continuously with the equipment that we have developed and reported previously, during the filling phase of urodynamic study (UDS). A total of 30 children (5-12 years old) are included in this prospective study. The equipment uses two dry electrodes embedded inside a strap to collect impedance and electrocardiogram signals. The factors affecting baseline BI and its decreases during UDS have been investigated. The median age is 6.1 years and BI is accurately measured in 27 out of 30 patients (90.0% accuracy). The median value of baseline BI is 1958 Ω. It is higher when they are older, equal to or taller than 125 cm, or non-neurogenic bladder patients. BI decreases as the bladder is filled with saline in 21 patients (77.8%), and remains constant in 6 patients (22.2%). The median age of the Decreased Group is significantly higher than that of Nondecreased Group (p = .036). Height of 125 cm or more is significant in the Decreased Group (p = .020). Heart rates also have been simultaneously measured and revealed a mild decrease during the filling phase. The baseline BI is affected by the height and age of the children. BI is effectively measured and reflects a change in the BV in older children who are taller than 125 cm, with a small device using a smartphone and a strap.

Impedimetric Detection and Electromediated Apoptosis of Vascular Smooth Muscle Using Microfabricated Biosensors for Diagnosis and Therapeutic Intervention in Cardiovascular Diseases.

Cardiovascular diseases remain a significant global burden with 1‐in‐3 of all deaths attributable to the consequences of the disease. The main cause is blocked arteries which often remain undetected. Implantable medical devices (IMDs) such as stents and grafts are often used to reopen vessels but over time these too will re‐block. A vascular biosensor is developed that can report on cellularity and is amenable to being mounted on a stent or graft for remote reporting. Moreover, the device is designed to also receive currents that can induce a controlled form of cell death, apoptosis. A combined diagnostic and therapeutic biosensor would be transformational for the treatment of vascular diseases such as atherosclerosis and central line access. In this work, a cell sensing and cell apoptosing system based on the same interdigitated electrodes (IDEs) is developed. It is shown that the device is scalable and that by miniaturizing the IDEs, the detection sensitivity is increased. Apoptosis of vascular smooth muscle cells is monitored using continuous impedance measurements at a frequency of 10 kHz and rates of cell death are tracked using fluorescent dyes and live cell imaging.

Disturbing-Free Determination of Yeast Concentration in DI Water and in Glucose Using Impedance Biochips.

Deionized water and glucose without yeast and with yeast (Saccharomyces cerevisiae) of optical density OD600 that ranges from 4 to 16 has been put in the ring electrode region of six different types of impedance biochips and impedance has been measured in dependence on the added volume (20, 21, 22, 23, 24, 25 µL). The measured impedance of two out of the six types of biochips is strongly sensitive to the addition of both liquid without yeast and liquid with yeast and modelled impedance reveals a linear relationship between the impedance model parameters and yeast concentration. The presented biochips allow for continuous impedance measurements without interrupting the cultivation of the yeast. A multiparameter fit of the impedance model parameters allows for determining the concentration of yeast (cy) in the range from cy = 3.3 × 107 to cy = 17 × 107 cells/mL. This work shows that independent on the liquid, i.e., DI water or glucose, the impedance model parameters of the two most sensitive types of biochips with liquid without yeast and with liquid with yeast are clearly distinguishable for the two most sensitive types of biochips.

Aptamer-Modified Microelectrodes for the Electrochemical Impedance Spectroscopy Detection of Neuropeptide Y

The design novel biosensors is a broad field including a wide range of applications including medical diagnostics and environmental monitoring. Small sizes of the electrodes have advantages used for selective identification of a biological target, such as voltammetric time scales, lower background noise and higher spatial resolution. Platinum and Carbon nanofiber has been some promising materials for fabrication of electrodes because of their electrical conductivity, chemical stability and high surface area. The intended application is to the possibility to create point of care diagnostics for monitoring the health of astronauts. Neuropeptides are short amino acid chains that are synthesized in the soma and dendrites, and they are stored in large dense core vesicles until released from nerve endings as well as from dendrites. Also, it’s not recycled and there is no reuptake system, but they are broken by peptidases, which require the cell to always synthesize new molecules to replace them by sending them from the soma to the nerve endings and dendrites. Other small neurotransmitters are normally released together with neuropeptides; therefore, it is essential to develop a technique for their detection as selective as possible and to have a strategy to cancel out the signal exerted by other neurotransmitters. The structural similarity between neuropeptides makes their detection impossible using common electrochemical techniques. Their study is currently done measuring the expression of neuropeptides in-vitro or using microdialysis coupled with mass spectrometry, which gives temporal resolution of tens of minutes. In this project, we have developed a modification protocol that reproducibly adds highly selective aptamers to the microelectrodes and the adsorption of neuropeptide Y differentially detected using microelectrodes. Based on the results, changes in concentration due to the release and absorption of neuropeptide Y can be followed with continuous electrochemical impedance measurements using microelectrodes, with the specificity provided by the used of aptamers in the surface of the microelectrodes.

Evaluation of the Parameter "Mean Impedance" for Representing Eustachian tube Functions During Pressure Increase and Decrease in Pressure Chamber Measurements.

The hypothesis of the study is that the mean impedance (MI) during compression and decompression provides additional information of the Eustachian tube (ET) function. The continuous impedance measurement in a pressure chamber can provide valuable information about the opening function of the ET. Around 55 ear-healthy volunteers were examined in a pressure chamber. These were subjected to a decompression phase and a compression phase. The pressure change was constantly 20 kPa/min. Using evaluation software, the MI could be determined for both ears in each case for the phases of compression and decompression. In 49 participants, we could interpret the data successfully. On average, an output value (without pressure changes) of the impedance of 0.58 ±0.11 Pa on the right side and 0.43 ± 0.1 Pa on the left side were measured. During decompression, 0.098 ± 0.05 Pa (right) and 0.087 ± 0.043 Pa (left) could be determined. For compression, values of 0.086 ± 0.044 Pa on the right and 0.079 ± 0.045 Pa on the left were detected. The retest reliability was higher with an intraclass correlation coefficient for the decompression MI of 0.833 than the 0.772 compression MI. It is possible to measure MI in healthy subjects during compression and decompression. This value represents a good average in terms of the pressure tolerance of the middle ear. In future, studies will be required to determine whether MI will be a useful parameter in differentiating normal and abnormal ET function.

Multifunctional and miniaturized flexible sensor patch: Design and application for in situ monitoring of epoxy polymerization

Sensor systems capable of in situ, continuous impedance measurements are expected to play an important role for a broad spectrum of applications. However, widespread use of these devices is hindered by their current form of separated sensors from bulky, expensive readout instruments. Moreover, the lack of other relevant sensing functionalities on the same system results in an incomplete understanding of the complex physical and chemical changes taking place. In this paper, a miniaturized sensor patch (MSP) with simultaneous impedance and temperature measurements and fully integrated readout is cleverly designed. By using an on-board microcontroller, sensor signal is read out locally and transmitted digitally, eliminating the noise on the signal over the transmission path. The MSP is stable over a wide temperature range (20–180 °C), and in various dielectric mediums (air, epoxies). Moreover, flexible circuit board technology based device fabrication permits further extended functionalities of the patch with off-the-shelf surface mounted devices. The MSPs were successfully applied for monitoring the polymerization processes of two epoxies, demonstrated the potential of the proposed sensor patch as an integrated and multifunctional sensing solution.

A cell impedance-based real-time in vitro assay to assess the toxicity of amphotericin B formulations

Aerosolized liposomal amphotericin B (L-AmB) has been investigated as prophylaxis against invasive aspergillosis. However, the clinical results are controversial and some trials suggest that toxicity could be a limitation for wider use. Our aim was to assess the dynamics of cell toxicity induced in a human alveolar epithelial cell line (A549) after exposure to L-AmB (50 to 400μg/ml) or amphotericin B deoxycholate (D-AmB; 50 to 200μg/ml) by monitoring real-time A549 cell viability using an impedance-based technology. Results were expressed as cell index values integrating cell adhesion, proliferation, and survival. In parallel, the gene expression of proinflammatory cytokines was quantified at 6 and 24h after drug addition by real-time RT-PCR on cell lysates. No sustained reduction of cell indexes was observed with L-AmB or empty liposomes, even at 400μg/ml. Only the highest concentration tested of L-AmB (400μg/ml) yielded transient significant 6-fold and 4-fold induction of TNF-α and IL-8 mRNAs, respectively. In contrast, D-AmB induced a decrease in cell indexes and only the 50μg/ml concentration of D-AmB was followed by cell recovery, higher concentrations leading to cell death. Significant 4-fold, 7-fold and 3-fold inductions of TNF-α, IL-8 and IL-33 mRNAs were also observed at 6h with 50μg/ml of D-AmB. In conclusion, continuous cell impedance measurement showed no toxicity on overall cellular behavior although a slight proinflammatory cytokine expression is possible after L-AmB challenge. Real-time kinetics of cell impedance is an interesting tool for initial screening of cell toxicity.

Impact of Mycotoxins Secreted by Aspergillus Molds on the Inflammatory Response of Human Corneal Epithelial Cells

Exposure to molds and mycotoxins not only contributes to the onset of respiratory disease, it also affects the ocular surface. Very few published studies concern the evaluation of the effect of mycotoxin exposure on ocular cells. The present study investigates the effects of aflatoxin B1 (AFB1) and gliotoxin, two mycotoxins secreted by Aspergillus molds, on the biological activity of the human corneal epithelial (HCE) cells. After 24, 48, and 72 h of exposure, cellular viability and inflammatory response were assessed. Both endpoint cell viability colorimetric assays and continuous cell impedance measurements, providing noninvasive real-time assessment of the effect on cells, were performed. Cytokine gene expression and interleukin-8 release were quantified. Gliotoxin appeared more cytotoxic than AFB1 but, at the same time, led to a lower increase of the inflammatory response reflecting its immunosuppressive properties. Real-time cell impedance measurement showed a distinct profile of cytotoxicity for both mycotoxins. HCE cells appeared to be a well-suited in vitro model to study ocular surface reactivity following biological contaminant exposure. Low, but persistent inflammation, caused by environmental factors, such as fungal toxins, leads to irritation and sensitization, and could be responsible for allergic manifestations which, in turn, could lead to mucosal hyper-reactivity.

P083 Method for continuous multichannel measurement of impedance at the auricular sites innervated by various cranial nerves

Question External auricule receives afferent supply via vagal, trigeminal and cervical nerves ( Peuker and Filler, 2002 ). Reduced impedance of the auricular sites innervated by vagal and trigeminal nerves is associated with pain and malfunction of internal organs ( Oleson et al., 1980 ; Saku et al., 1993 ). The aim was to develop the robust method for continuous measurement of skin impedance at the sites of auricle, supplied by various cranial nerves. Methods Multichannel device for continuous impedance measurement, based on Atmel ATmega16 microprocessor with 1 kHz of probing alternating current frequency was controlled using Matlab environment via USB port. The device measures voltage difference between the reference electrode (right forearm) and the sites of interest (innervation areas of cranial nerves) and transforms the voltage values into impedance using the calibration measurements of known resistances. Surface ECG and stainless steel needle electrodes were used at the sites of interest on the right auricles of healthy volunteers. Impedance monitoring was performed at rest and under the heat pain stimuli, delivered via CHEPS thermode (MEDOC analyser, Israel). Results Reproducible stable data with the voltage of 1 V, current values of 100 μ A and impedance around 10 k Ω were acquired (Fig. 1 Download : Download high-res image (306KB) Download : Download full-size image ), whereas invasive measurement yielded less variable data than non- invasive procedure. Heat pain stimulation led to differential reduction of the impedance in the sites of cranial nerve innervation (Fig. 2), whereas the decreased impedance recovered to the baseline values (Fig. 2 Download : Download high-res image (266KB) Download : Download full-size image ). Conclusions The multichannel continuous measurement of impedance at the external auricle was feasible. Further investigations are warranted to clarify the differential impedance response from the auricular sites in healthy subjects under stress challenge and patients.

Genetic variation and dynamics of infections of equine herpesvirus type 5 (EHV-5) in individual horses

without antiviral) to 45% and 100% in presence of Acyclovir (10ml/ mL and 100 mg/mL, respectively). These results are correlated with the decreased of viral load measured in the presence of Acyclovir: 1010 genome copies/mLwith EHV-1 only,106 copies/mL with EHV-1 + Acyclovir 10 mg/mL and 105 copies/mLwith EHV-1 + Acyclovir 100 mg/ mL. In conclusion, the cellular impedance monitoring system is a new real-time method to monitor cell growth and viral proliferation in cell cultures. This technology is well adapted for high-throughput screening of antiviral molecules. In fact, the xCELLigence system enables continuous impedance measurement and quantification of cell adhesion, proliferation, cell death and detachment during viral infection.

Real-time monitoring of Equid herpesviruses infectivity in equine dermal cell based on impedance measurements

In virology, different conventional methods are commonly used for virus titration and infectivity studies. Most of them are based on direct examination of viral cytopathic effect, which is time consuming, tedious and requires an endpoint reading. The RTCA xCELLigence system (ACEA Biosciences) has been developed to follow cellular events and their dynamics in real time using a micro-electrical biosensor technology. The aim of this study was to evaluate the feasibility of using this biosensor technology to measure the effect of different equid herpesviruses on equine dermal cell cultures, with or without antiviral acyclovir treatment. Cells were infected with EHV-1 (VR700), EHV-4 (VR2230), EHV-2 (VR701) or EHV-3 (VR352). The viral effects were monitored by 3 different methods: impedance measurements (RTCA), cytopathic effects recording (microscopy) and viral load quantification (qPCR). The RTCA technology showed a dose dependent drop of the cellular index induced by specific impedance variations measured during growth of each virus tested. These results correlated with the cytopathic effect induced by the different herpesvirus species, as well as viral loads measured by qPCR. For example, after 3 days of incubation with EHV-1, RTCA results showed an increase of the cellular index from 0% (infection without antiviral) to 45% and 100% in presence of Acyclovir (10μl/mL and 100 μg/mL, respectively). These results are correlated with the decreased of viral load measured in the presence of Acyclovir: 1010 genome copies/mL with EHV-1 only, 106 copies/mL with EHV-1 + Acyclovir 10 μg/ mL and 105 copies/mL with EHV-1 + Acyclovir 100 μg/ mL. In conclusion, the cellular impedance monitoring system is a new real-time method to monitor cell growth and viral proliferation in cell cultures. This technology is well adapted for high-throughput screening of antiviral molecules. In fact, the xCELLigence system enables continuous impedance measurement and quantification of cell adhesion, proliferation, cell death and detachment during viral infection.

Characterizing the active opening of the eustachian tube in a hypobaric/hyperbaric pressure chamber.

Active and passive opening of the Eustachian tube (ET) enables direct aeration of the middle ear and a pressure balance between middle ear and the ambient pressure. The aim of this study was to characterize standard values for the opening pressure (ETOP), the opening frequency (ETOF), and the opening duration (ETOD) for active tubal openings (Valsalva maneuver, swallowing) in healthy participants. In a hypobaric/hyperbaric pressure chamber, 30 healthy participants (19 women, 11 men; mean age, 25.57 ± 3.33 years) were exposed to a standardized profile of compression and decompression. The pressure values were recorded via continuous impedance measurement during the Valsalva maneuver and swallowing. Based on the data, standard curves were identified and the ETOP, ETOD, and ETOF were determined. Recurring patterns of the pressure curve during active tube opening for the Valsalva maneuver and for active swallowing were characterized. The mean value for the Valsalva maneuver for ETOP was 41.21 ± 17.38 mbar; for the ETOD, it was 2.65 ± 1.87 seconds. In the active pressure compensation by swallowing, the mean value for the ETOP was 29.91 ± 13.07 mbar; and for the ETOD, it was 0.82 ± 0.53 seconds. Standard values for the opening pressure of the tube and the tube opening duration for active tubal openings (Valsalva maneuver, swallowing) were described, and typical curve gradients for healthy subjects could be shown. This is another step toward analyzing the function of the tube in compression and decompression.

Dynamic electrochemical impedance spectroscopy reconstructed from continuous impedance measurement of single frequency during charging/discharging

In this study, a novel implementation of dynamic electrochemical impedance spectroscopy (DEIS) is proposed. The method first measures the impedance continuously at a single frequency during one charging/discharging cycle, then repeats the measurement at a number of other selected frequencies. The impedance spectrum at a specific SOC is obtained by interpolating and collecting the impedance at all of the selected frequencies. The charge transfer resistance, Rct, from the DEIS is smaller than that from the steady EIS in a wide state-of-charge (SOC) range from 0.4 to 1.0, the Rct during charging is generally smaller than that during discharging for the battery chemistry used in this study.

Textrode-enabled transthoracic electrical bioimpedance measurements – towards wearable applications of impedance cardiography

Abstract During the last decades the use of electrical bioimpedance (EBI) in the medical field has been the subject of extensive research, as an affordable, harmless and non-invasive technology. In some specific applications, such as body composition assessment where EBI has proven a good degree of effectiveness and reliability, the use of textile electrodes and measurement garments have shown good performance and reproducible results. Impedance cardiography (ICG) is a modality of EBI that can benefit from the implementation and use of wearable sensors. ICG is based on continuous impedance measurements of a longitudinal segment across the thorax taken at a single frequency. The need for a specific electrode placement on the thorax and neck can be easily ensured with the use of a garment with embedded textile electrodes, also known as “textrodes.” The first step towards the implementation of garment-based ICG is to determine the quality of ICG measurements with textile sensors to allow estimation of fundamental ICG parameters. In this work, the measurement performance of a 2-belt set with incorporated textrodes for thorax and neck is compared against ICG measurements obtained with Ag/AgCl electrodes. The analysis is based on the quality of the fundamental ICG signals (ΔZ, dZ/dt and ECG), systolic time intervals and other ICG parameters. The results indicate the feasibility of using textrodes for ICG measurements with consistent measurements and relatively low data dispersion. Thus, enabling the development of measuring garments for ICG measurements.