Distribution by Scientific Domains
Distribution within Engineering

Kinds of Impedance

  • ac impedance
  • bioelectrical impedance
  • characteristic impedance
  • electrical impedance
  • electrode impedance
  • input impedance
  • intraluminal impedance
  • lead impedance
  • multichannel intraluminal impedance
  • surface impedance

  • Terms modified by Impedance

  • impedance analysis
  • impedance bandwidth
  • impedance change
  • impedance characteristic
  • impedance control
  • impedance function
  • impedance matching
  • impedance matrix
  • impedance measurement
  • impedance monitoring
  • impedance parameter
  • impedance resonator
  • impedance response
  • impedance signal
  • impedance spectroscopy
  • impedance spectroscopy measurement
  • impedance spectrum
  • impedance tensor
  • impedance tomography

  • Selected Abstracts

    Surface Design in Solid-State Dye Sensitized Solar Cells: Effects of Zwitterionic Co-adsorbents on Photovoltaic Performance

    Mingkui Wang
    Abstract In solid-state dye sensitized solar cells (SSDSCs) charge recombination at the dye-hole transporting material interface plays a critical role in the cell efficiency. For the first time we report on the influence of dipolar co-adsorbents on the photovoltaic performance of sensitized hetero-junction solar cells. In the present study, we investigated the effect of two zwitterionic butyric acid derivatives differing only in the polar moiety attached to their common 4 carbon-chain acid, i.e., 4-guanidinobutyric acid (GBA) and 4-aminobutyric acid (ABA). These two molecules were implemented as co-adsorbents in conjunction with Z907Na dye on the SSDSC. It was found that a Z907Na/GBA dye/co-adsorbent combination increases both the open circuit voltage (Voc) and short-circuit current density (Jsc) as compared to using Z907Na dye alone. The Z907Na/ABA dye/co-adsorbent combination increases the Jsc. Impedance and transient photovoltage investigations elucidate the cause of these remarkable observations. [source]

    High-frequency Impedance and Sensitivity of Micro-fluxgate Sensors Fabricated with Cobalt Base Amorphous Films

    Kwang-Ho Shin Non-member
    Abstract Micro-fluxgate sensors 2 mm long, 1.5 mm wide were fabricated with CoZrNb amorphous films. Their high-frequency input/output impedance was measured and evaluated to investigate whether the sensor output and/or sensitivity could be estimated by the complex impedance, especially the reactance. The output reactance changed from 11.1 to 6.1 ohm at 8 MHz by applying the external magnetic field of 10.5 Oe, whereas the input impedance changed from 12.3 to 10.1 ohm. The parasitic capacitance was driven from the measured reactance and resonance frequency. The inductance and inductive reactance could be evaluated with the parasitic capacitance and measured reactance. The tendency of output voltage dependent on frequency is similar to that of inductive reactance. The sensitivity of the fabricated sensor was 17.6 mV/VOe at 8 MHz. Copyright © 2008 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [source]

    An investigation into the relationship between apical root Impedance and canal anatomy

    S. M. Ardeshna
    Aim, To investigate a possible relationship between apical root impedance and canal anatomy. Methodology, Twenty-three roots from human extracted teeth (mostly single rooted but also from molars) with different apical anatomy were selected. The apical anatomy was initially classified by staining the root tip to identify number of canal exits; after impedance measurements, the anatomy was confirmed by staining and clearing the dentine. The roots were divided into two groups; 12 had simple (S) anatomy (Vertucci type 1 with a single exit) and 11 had complex (C) anatomy (various Vertucci canal types with multiple exist). Impedance measurements were taken using a frequency response analyser at seven levels in the root (0.0, 0.5, 1.0, 2.0, 3.0, 4.0 and 5.0 mm short of the apical terminus) at 14 frequencies ranging from 1120 to 100 000 Hz. Care was taken to control the temperature and other variables that could confound measurement accuracy. The impedance characteristics of individual roots were compared with 37 equivalent circuits (based on a pool created from a previous study); the best fitting equivalent circuit was selected. The equivalent circuits were used as the single outcome measure describing the impedance characteristics and correlated with the canal anatomy (S/C). Generalized estimating equations were used to perform logistic regression to analyse the data. Results, Canal anatomy had a significant (P = 0.046) effect on the equivalent circuit model. One circuit (model 10) was found to be the commonest and occurred significantly more commonly in the simple canals. The odds of prevalence of circuit model 10 were 2.2 times (odds ratio 2.17, 95% confidence interval 1.01,4.63) higher in canals with simple anatomy compared with canals with complex anatomy. Conclusions, Canal anatomy had a significant effect on the equivalent circuit describing its impedance characteristics. It should be possible to use impedance spectroscopy to clinically predict and image apical canal complexities. [source]

    Intraoperative Comparison of a Subthreshold Test Pulse with the Standard High-Energy Shock Approach for the Measurement of Defibrillation Lead Impedance

    There are two methods to measure shocking lead impedance: delivery of high-energy shocks that require patient sedation, and the painless measurement of impedance from subthreshold test pulses. The aim of this study was to compare the two methods. Methods: The study included 131 patients implanted with a standard DR (n = 71) or VR (n = 60) ICD connected to either single-coil (n = 39) or dual-coil (n = 92) defibrillation leads. The noninvasive high-energy impedance test was done using a 17 J shock after induction of ventricular tachyarrhythmias and compared to a 0.4 ,J test pulse used by the ICD for the subthreshold measurements. Results: Defibrillation lead impedance measurements were not significantly different between patients with the same shocking vector configuration. In patients with a single-coil defibrillation lead the impedance was 62 ± 9 , with the high-energy shock and 62 ± 8 , with the subthreshold test pulses (P = 0.13). Patients with a dual-coil configuration recorded average impedances of 40 ± 5 , from both tests (P = 0.44). While there was no difference in values recorded within each lead configuration, there was a significant difference in impedance between the single-coil and the dual-coil patient groups (P = 0.001). Conclusions: There was no significant difference between shocking lead impedances measured with the high-energy shock or the subthreshold test pulses. This offers the possibility of noninvasive, low-energy serial measurements of shocking lead impedance at follow-up visits and removing the need for sedation. [source]

    Positive end-expiratory pressure optimization using electric impedance tomography in morbidly obese patients during laparoscopic gastric bypass surgery

    K. Erlandsson
    Background:, Morbidly obese patients have an increased risk for peri-operative lung complications and develop a decrease in functional residual capacity (FRC). Electric impedance tomography (EIT) can be used for continuous, fast-response measurement of lung volume changes. This method was used to optimize positive end-expiratory pressure (PEEP) to maintain FRC. Methods:, Fifteen patients with a body mass index of 49 ± 8 kg/m2 were studied during anaesthesia for laparoscopic gastric bypass surgery. Before induction, 16 electrodes were placed around the thorax to monitor ventilation-induced impedance changes. Calibration of the electric impedance tomograph against lung volume changes was made by increasing the tidal volume in steps of 200 ml. PEEP was titrated stepwise to maintain a horizontal baseline of the EIT curve, corresponding to a stable FRC. Absolute FRC was measured with a nitrogen wash-out/wash-in technique. Cardiac output was measured with an oesophageal Doppler method. Volume expanders, 1 ± 0.5 l, were given to prevent PEEP-induced haemodynamic impairment. Results:, Impedance changes closely followed tidal volume changes (R2 > 0.95). The optimal PEEP level was 15 ± 1 cmH2O, and FRC at this PEEP level was 1706 ± 447 ml before and 2210 ± 540 ml after surgery (P < 0.01). The cardiac index increased significantly from 2.6 ± 0.5 before to 3.1 ± 0.8 l/min/m2 after surgery, and the alveolar dead space decreased. PaO2/FiO2, shunt and compliance remained unchanged. Conclusion:, EIT enables rapid assessment of lung volume changes in morbidly obese patients, and optimization of PEEP. High PEEP levels need to be used to maintain a normal FRC and to minimize shunt. Volume loading prevents circulatory depression in spite of a high PEEP level. [source]

    Evolution of Brain Impedance in Dystonic Patients Treated by GPi Electrical Stimulation

    NEUROMODULATION, Issue 2 2004
    Simone Hemm BME.
    Abstract Deep Brain Stimulation is an effective treatment of generalized dystonia. Optimal stimulation parameters vary between patients. This article investigates the influence of electrical brain impedance and delivered current on the brain response to stimulation. Twenty-four patients were bilaterally stimulated in the globus pallidus internus through two implanted four-contact electrodes. The variation of brain impedance and current measurements was correlated with stimulation parameters, time course, and clinical outcome. When a contact was activated, a statistically significant and reversible decrease of brain impedance was found. Impedance and current values and their variations with time significantly differed between patients. The absolute impedance did not significantly correlate with the final outcome. We conclude that the reversible decrease of impedance reflects an adaptive long-term mechanism, which could be due to a plasticity phenomenon, but has no prognostic value. Impedance and current measurements give new complementary information for parameter adjustment and trouble shooting and should therefore be included in all patients' follow-up. [source]

    Subthreshold Test Pulses Versus Low Energy Shock Delivery to Estimate High Energy Lead Impedance in Implanted Cardioverter Defibrillator Patients

    VOLLMANN, D., et al.: Subthreshold Test Pulses Versus Low Energy Shock Delivery to Estimate High Energy Lead Impedance in Implanted Cardioverter Defibrillator Patients. The high energy lead impedance is valuable for detecting lead failure in ICDs, but until recently shock delivery was necessary for high energy impedance measurement. This study compared the use of subthreshold test pulses and low energy test shocks to estimate the high energy impedance. Immediately after implantation of Ventak Prizm ICDs in 29 patients, the lead impedance was measured with five subthreshold (0.4 ,J) test pulses, 5 low energy (1.1 J) shocks, and two to three high energy(16 ± 4.5 J)shocks. The mean impedances measured using high energy shocks, low energy shocks, and subthreshold pulses were42.0 ± 7.3 ,, 46.5 ± 8.1 ,, and42.4 ± 7.1 ,, respectively. The impedances measured using high and low energy shocks differed significantly(P <0.0001), while those obtained by high energy shocks and low energy pulses did not(P = 0.63). According to the Pearson correlation coefficient, the impedance measurements with subthreshold pulses and low energy shocks were both closely correlated(P < 0.0001)with impedance values determined with high energy shocks. However, while the impedance values tended to be higher when measured with low energy shocks, the concordance correlation coefficient (c) was higher for subthreshold test pulse versus high energy shock(c = 0.92)than for low versus high energy shock(c = 0.73). Furthermore, the intraindividual variability of impedance measurements was lower with subthreshold pulse measurements than with low energy shocks. Compared with low energy shocks, impedance measurement with subthreshold pulses has higher reproducibility and a higher correlation with the impedance obtained by high energy shock delivery. Safe and painless high energy impedance estimation with subthreshold pulses might, therefore, help to detect ICD lead failure during routine follow-up. (PACE 2003; 26:[Pt. II]:457,460) [source]

    Clinical Use of Intracardiac Impedance: Current Applications and Future Perspectives

    ARTHUR, W., et al.: Clinical Use of Intracardiac Impedance: Current Applications and Future Perspectives. For over 40 years the measurement of intracardiac impedance has been proposed as a method of assessing the contractile state of the heart muscle. This technique requires the positioning of one or more intracavitary electrodes and the generation of an electric field from an alternating current source. Variations in the calculated impedance signal reflect changes in the ventricular blood pool volume adjacent to the electrodes. Intracardiac impedance measurement has been successfully developed as a research tool to assess myocardial contractility, and from this, clinical uses have evolved. Commercial rate responsive pacing systems use intracardiac impedance to assess the inotropic state of the heart. Further development of this technology might allow hemodynamic discrimination of cardiac arrhythmias. [source]

    Real time monitoring of drug metabolic enzyme response inside human hepatoma GS-3A4-HepG2 cells by means of electrochemical impedance measurement

    Masaaki Kobayashi
    Abstract Cytochrome P-450s (CYPs) are important biopolymers for the maintenance of cellular function. If metabolic activity of the CYP in the cells can be estimated, so can the function of metabolism, which is closer to the organism. In this research, the method of measuring the drug metabolic activity inside the cell by making use of an electrochemical technique was examined. Human hepatoma GS-3A4-HepG2 cells of which the cytochrome P-4503A4 (CYP3A4) drug metabolic activity is found to be the same as that of primary hepatocytes were used in the experiment. The GS-3A4-HepG2 cells were cultured on an indium-tin oxide (ITO) electrode until they became confluent. Substrate testosterone and inhibitor ketoconazole of CYP3A4 were exposed to cells cultured on an ITO electrode, and the reaction was observed by noting the electrochemical impedance measurement. Impedance was decomposed into the resistance component and the reactance component, and each was examined in detail. As a result, according to testosterone concentration change, there was a remarkable time change in the reactance component. A similar impedance measurement was done by using human hepatoma HepG2 cells in which the drug metabolic activity had extremely decreased. Nevertheless, no time change in the reactance component that was noticed in GS-3A4-HepG2 cells was observed. Next, the amount of metabolite in the solution after impedance measurement was measured by means of liquid chromatography-tandem mass spectroscopy (LC-MS/MS). In the experiment with GS-3A4-HepG2 cells, a testosterone concentration-dependent correlation was observed between the reactance component change and the amount of metabolite. But, in the impedance measurement by ketoconazole, the change in reactance components was not observed in either the GS-3A4-HepG2 cells or the HepG2 cells. Ketoconazole and the heme iron in CYP3A4 effect the coordination bond, but ketoconazole was not metabolized by CYP3A4. It was confirmed that the time change in the reactance component which was caused by the testosterone was detected neither in the cells that take up the substrate, nor in the coordination bond between the CYP enzyme and the drug. Therefore, the time change in the remarkable reactance component observed by this electrochemical impedance measurement is dependent on drug metabolic activity. An electrochemical drug metabolic activity measuring method with the human hepatoma GS-3A4-HepG2 cells was able to be established. Copyright © 2004 John Wiley & Sons, Ltd. [source]

    Electrochemical Quartz Crystal Impedance and Fluorescence Quenching Studies on the Binding of Carbon Nanotubes (CNTs)-Adsorbed and Solution Rutin with Hemoglobin

    Yuhua Su
    Electrochemical quartz crystal impedance (QCI) technique was utilized to monitor in situ the adsorption of rutin (RT) onto a carbon nanotubes (CNTs)-modified gold electrode and to study the binding process of solution hemoglobin (Hb) to RT immobilized on the electrode. Time courses of the QCI parameters including crystal resonant frequency were simultaneously obtained during the RT adsorption and Hb-RT binding. In contrast to the negligible RT adsorption at a bare gold electrode, the modification by CNTs notably enhanced the amount of adsorption, and almost all of the adsorbed RT molecules were found to be electroactive. On the basis of the frequency response from the binding of adsorbed RT to solution Hb and the diminished electroactivity of adsorbed RT after the formation of the electrochemically inactive RT-Hb adduct, the average binding molar ratio of adsorbed RT to Hb was estimated to be 23.9:1, and the association constant (Ka) for the binding was estimated to be 2.87 × 106 (frequency) and 3.92 × 106 (charge) L mol,1, respectively. Comparable results were obtained from fluorescence quenching measurements in mixed solutions containing RT of fixed concentration and Hb of varying concentrations, demonstrating that the interfacial RT here behaved equivalently in the RT-Hb binding activity compared to that in solution. This work may have presented a new and general protocol involving CNTs to study many other electroactive natural antioxidants or drugs that are at the interface or in solution, their binding with proteins or other biomolecules, and changes of their antioxidant activity after the binding. [source]

    ChemInform Abstract: Determination of the Sodium Ion Transference Number of the Dion,Jacobson-Type Layered Perovskite NaCa2Nb3O10 Using ac Impedance and dc Methods.

    CHEMINFORM, Issue 24 2002
    V. Thangadurai
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

    Nutritional status of children with coeliac disease

    ACTA PAEDIATRICA, Issue 7 2010
    B Aurangzeb
    Abstract Aims:, The main aim of this study was to assess the nutritional status of children with newly diagnosed Coeliac disease (CD)with comparison to matched controls. A further aim was to assess relationships between presentation patterns and nutrition in childhood CD. Methods:, The nutritional status of newly diagnosed CD was assessed by anthropometry, Bioelectrical Impedance and serum leptin levels, and contrasted to age and gender matched controls. Results:, Twenty-five children with CD (mean age of 8.2 ± 4.5 years) and 25 control children (mean age 8.1 ± 4.4.) were enrolled. Thirteen (52%) children with CD had gastrointestinal symptoms with 14 having a family history of CD. At presentation 8.7% were wasted, 4.2% were stunted and 20.8% overweight, although none were obese. Mean height and weight for age, other nutritional parameters and serum leptin did not differ between the groups. Serum leptin correlated with BMI in both groups. Conclusions:, Children with CD more commonly present with atypical symptoms than with classical features. Variations in nutrition (under to overnutrition) may be seen at diagnosis, without relationship to the presence of symptoms. Leptin levels were not altered specifically in the setting of CD. Nutritional assessment remains important in the assessment and management of CD in children. [source]

    Prevalence of Sleep Disordered Breathing in a Heart Failure Program

    Robin J. Trupp MSN
    Recent data show that a high percentage of patients with systolic left ventricular dysfunction have sleep-disordered breathing (SDB), contributing to the incidence of morbidity and mortality in heart failure. This study examines the prevalence of sleep disorders in stable heart failure patients regardless of ejection fraction. On three consecutive days in a heart failure clinic, all patients were asked to participate in a screening for SDB. This screening involved the placement of an outpatient device (ClearPath, Nexan, Inc., Alpharetta, GA), which collects thoracic impedance, oxyhemoglobin saturation, and 2-lead electrocardiogram data. Sixteen patients (42%) had moderate or severe SDB, and 22 patients (55%) had mild or no significant SDB. Fourteen of the 16 patients with moderate or severe SDB subsequently received treatment by confirming SDB and the continuous positive airway pressure in a sleep lab. Forty-two percent of patients with stable heart failure presenting to a heart failure clinic screened positive for SDB, despite receiving optimal standard of care. [source]

    Diagnosis of Nonmelanoma Skin Cancer/Keratinocyte Carcinoma: A Review of Diagnostic Accuracy of Nonmelanoma Skin Cancer Diagnostic Tests and Technologies

    BACKGROUND Nonmelanoma skin cancer (NMSC) is the most prevalent cancer in the light-skinned population. Noninvasive treatment is increasingly used for NMSC patients with superficial lesions, making the development of noninvasive diagnostic technologies highly relevant. OBJECTIVE The scope of this review is to present data on the current state-of-the-art diagnostic methods for keratinocyte carcinoma: basal cell carcinoma, squamous cell carcinoma, and actinic keratosis. METHODS AND MATERIALS MEDLINE, BIOSIS, and EMBASE searches on NMSC and physical and clinical examination, biopsy, molecular marker, ultrasonography, Doppler, optical coherence tomography, dermoscopy, spectroscopy, fluorescence imaging, confocal microscopy, positron emission tomography, computed tomography, magnetic resonance imaging, terahertz imaging, electrical impedance and sensitivity, specificity, and diagnostic accuracy. RESULTS State-of-the-art diagnostic research has been limited in this field, but encouraging results from the reviewed diagnostic trials have suggested a high diagnostic accuracy for many of the technologies. Most of the studies, however, were pilot or small studies and the results would need to be validated in larger trials. CONCLUSIONS Some of these new imaging technologies have the capability of providing new, three-dimensional in vivo, in situ understanding of NMSC development over time. Some of the new technologies described here have the potential to make it from the bench to the clinic. [source]

    Subclinical vascular alterations in young adults with type 1 diabetes detected by arterial tonometry

    I. Barchetta
    Abstract Background Diabetes mellitus is characterized by a very high prevalence of atherosclerotic disease. Aims of this study were to determine arterial compliance parameters in type 1 diabetes (T1D) patients as an expression of early pre-clinical endothelial dysfunction and to evaluate the impact of glucose exposure parameters such as the duration of diabetes and glycosylated haemoglobin (HbA1c) on the risk of developing alterations in vascular compliance. Methods 23 patients with uncomplicated type 1 diabetes (mean age: 32.78 ± 9.06 years, mean disease duration: 10.78 ± 7.51 years, mean HbA1c levels: 7.7 ± 1.9) and 26 age- and sex-matched healthy subjects (mean age: 32.3 ± 8.51 years) were recruited. In these subjects, we evaluated arterial compliance by calibrated tonometry (HDI/PulsewaveÔ CR-2000). Parameters included the following: large artery elasticity (C1), small artery elasticity (C2), systemic vascular resistance (SVR) and total vascular impedance (TVI). Results Patients with longer duration of T1D (>10 years) showed significant alterations in C2 (4.97 ± 2.7 mL/mmHg × 100) and in SVR (1464.67 ± 169.16 dina × s × cm,5) when compared with both healthy individuals (C2: 8.28 ± 2.67 mL/mmHg × 100, p = 0.001; SVR: 1180.58 ± 151.55 dina × s × cm,5, p = 0.01) and patients with recent-onset disease (,10 years) (C2: 10.02 ± 3.6 mL/mmHg × 100, p < 0.001; SVR: 1124.18 ± 178.5 dina × s × cm,5, p < 0.000). Both disease duration and HbA1c independently predicted impaired arterial compliance. Conclusions Young adult T1D patients with no signs of disease complication have detectable vessel wall abnormalities, particularly of small arteries, suggestive of hyperglycaemia-related early endothelial dysfunction. Copyright © 2009 John Wiley & Sons, Ltd. [source]

    Inter-observer agreement for multichannel intraluminal impedance,pH testing

    K. Ravi
    SUMMARY Twenty-four-hour ambulatory multichannel intraluminal impedance (MII),pH detects both acid and nonacid reflux (NAR). A computer-based program (AutoscanÔ, Sandhill Scientific, Highlands Ranch, CO, USA) automates the detection of reflux episodes, increasing the ease of study interpretation. Inter-observer agreement between multiple reviewers and with AutoscanÔ for the evaluation of significant NAR with MII,pH has not been studied in the adult population. Twenty MII,pH studies on patients taking a proton pump inhibitor twice daily were randomly selected. AutoscanÔ analyzed all studies using the same pre-programmed parameters. Four reviewers interpreted the MII,pH studies, adding or deleting reflux episodes detected by AutoscanÔ. Positive studies for NAR and total reflux episodes were based on published criteria. Cohen's kappa statistic (,) evaluated inter-observer agreement between reviewers and AutoscanÔ analysis. The average , for pathologic NAR between reviewers was 0.57 (0.47,0.70), and between reviewers and AutoscanÔ was 0.56 (0.4,0.8). When using the total reflux episode number as a marker for pathologic reflux (acid and NAR), the , score was 0.72 (0.61,0.89) between reviewers, and 0.74 (0.53,0.9) when evaluating total reflux episodes. Two reviewers agreed more often with each other and with AutoscanÔ on the number of NAR episodes, while the other two reviewers agreed with each other, but did not agree with either AutoscanÔ or the first two reviewers. Inter-observer agreement between reviewers and AutoscanÔ for detecting pathologic NAR is moderate, with reviewers either excluding more of the AutoscanÔ-defined events or excluding fewer events and therefore agreeing with AutoscanÔ. [source]

    Multichannel intraluminal impedance for the assessment of post-fundoplication dysphagia

    T. Yigit
    SUMMARY., Dysphagia often occurs after fundoplication, although its pathophysiology is not clear. We sought to better understand postfundoplication dysphagia by measuring esophageal clearance with multichannel intraluminal impedance (MII) along with more traditional work-up (manometry, upper gastrointestinal imaging [UGI], endoscopy). We evaluated 80 consecutive patients after laparoscopic fundoplication between April 2002 and November 2004. Patients were evaluated clinically and underwent simultaneous manometry and MII, 24-hour pH monitoring, endoscopy, and UGI. For analysis, patients were divided into the following groups based on the presence of dysphagia and fundoplication anatomy (by UGI/endoscopy): (1) Dysphagia and normal anatomy; (2) Dysphagia and abnormal anatomy; (3) No dysphagia and abnormal anatomy; and (4) No dysphagia and normal anatomy. Patients with dysphagia (Groups 1 & 2) had similar peristalsis (manometry), but were more likely to have impaired clearance by MII (32 pts, 62%) than those without dysphagia (9 pts, 32%, P = 0.01). Patients with abnormal anatomy (Groups 2 & 3) were also more likely to have impaired esophageal clearance (66%vs. 38%, P = 0.01). Finally, of patients that had normal fundoplication anatomy, those with dysphagia were much more likely to have impaired clearance (12 pts, 52%) than those with dysphagia (4 pts, 21%, P = 0.03). MII after fundoplication provides objective evidence of esophageal clearance, and is commonly abnormal in patients with abnormal fundoplication anatomy and/or dysphagia. Esophageal clearance is impaired in the majority of patients with postoperative dysphagia, even with normal fundoplication anatomy and normal peristalsis. MII may detect disorders in esophageal motility not detected by manometry. [source]

    A practical method for estimating dynamic soil stiffness on surface of multi-layered soil

    Naohiro Nakamura
    Abstract It is important to estimate the influence of layered soil in soil,structure interaction analyses. Although a great number of investigations have been carried out on this subject, there are very few practical methods that do not require complex calculations. In this paper, a simple and practical method for estimating the horizontal dynamic stiffness of a rigid foundation on the surface of multi-layered soil is proposed. In this method, waves propagating in the soil are traced using the conception of the cone model, and the impulse response function can be calculated directly and easily in the time domain with a good degree of accuracy. The characteristics of the impedance, that is the transformed value to the frequency domain of the obtained impulse response, are studied using two- to four-layered soil models. The cause of the fluctuation of impedance is expressed clearly from its relation to reflected waves from the lower layer boundary in the model. Copyright © 2005 John Wiley & Sons, Ltd. [source]

    Feasibility of using impedance-based damage assessment for pipeline structures

    Gyuhae Park
    Abstract This paper presents the feasibility of using an impedance-based health monitoring technique in monitoring a critical civil facility. The objective of this research is to utilize the capability of the impedance method in identifying structural damage in those areas where a very quick condition monitoring is urgently needed, such as in a post-earthquake analysis of a pipeline system. The basic principle behind this technique is to utilize high-frequency structural excitation (typically greater than 30 kHz) through surface-bonded piezoelectric sensors/actuators to detect changes in structural point impedance due to the presence of damage. Real-time damage detection in pipes connected by bolted joints was investigated, and the capability of the impedance method in tracking and monitoring the integrity of the typical civil facility has been demonstrated. Data collected from the tests illustrates the capability of this technology to detect imminent damage under normal operating conditions and immediately after a natural disaster. Copyright © 2001 John Wiley & Sons, Ltd. [source]

    Estimation of backward impedance on low-voltage distribution system using measured resonant current

    Toru Miki
    Abstract Two estimation methods for a backward impedance of a power distribution system are proposed in this paper. According to the first method, the backward impedance is estimated based on information obtained from the frequency response of a transient current flowing into a capacitor connected to a distribution line. The backward impedance is determined from the attenuation constant and the resonant frequency calculated using the capacitance and the impedance of the power distribution system. These parameters can be reliably obtained from a frequency response of the transient current using the least square method. The accuracy of the method strongly depends on the origin on the time axis for Fourier transform. An additional estimate of the time-origin is required for an accurate estimation of the backward impedance. The second method estimates the backward impedance using two transient current waveforms obtained by alternately connecting different capacitors to a distribution line. The backward impedance can be represented as a function of the frequency responses of these currents. Since this method is independent from the time-origin, it is suitable for automatic measurements of the backward impedance. Proposed methods are applicable to the estimation of harmonic currents in distribution systems. In this paper, harmonic currents flowing through a distribution line are calculated based on the estimated backward impedance and on the measured values of voltage harmonics obtained by the instrument developed by the authors. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 171(3): 28,40, 2010; Published online in Wiley InterScience ( DOI 10.1002/eej.20900 [source]

    Electronic Tongues Employing Electrochemical Sensors

    ELECTROANALYSIS, Issue 14 2010
    Manel del, Valle
    Abstract This review presents recent advances concerning work with electronic tongues employing electroanalytical sensors. This new concept in the electroanalysis sensor field entails the use of chemical sensor arrays coupled with chemometric processing tools, as a mean to improve sensors performance. The revision is organized according to the electroanalytical technique used for transduction, namely: potentiometry, voltammetry/amperometry or electrochemical impedance. The significant use of biosensors, mainly enzyme-based is also presented. Salient applications in real problem solving using electrochemical electronic tongues are commented. [source]

    A Contactless Impedance Probe for Simple and Rapid Determination of the Ratio of Liquids with Different Permittivities in Binary Mixtures

    ELECTROANALYSIS, Issue 1 2009
    Franti, ek Opekar
    Abstract Simple contactless cells with planar or tubular electrodes have been designed for measurement of the permittivity of solutions. The cells, connected to an integrated circuit of astable multivibrator, respond primarily to the capacitance component of the cell impedance, the multivibrator frequency depends in a defined manner on the solution permittivity and is readily used as the analytical signal in determinations of the ratios of components in binary liquid mixtures; water solution of methanol, ethanol and dioxane have been tested. The response of the cell with planar electrodes satisfies well the simple theoretical model and both the cells provide results with a sufficient sensitivity, a low LOD value (units of %vol) and a good precision (around 1%rel). The cell simplicity, small dimensions, long-term stability and the possibility of powering them from a battery make them suitable for hand-held meters. As an example of application in practice, the content of ethanol was determined in the car fuel petrol. [source]

    Label-Free Impedance Biosensors: Opportunities and Challenges

    ELECTROANALYSIS, Issue 12 2007
    Abstract Impedance biosensors are a class of electrical biosensors that show promise for point-of-care and other applications due to low cost, ease of miniaturization, and label-free operation. Unlabeled DNA and protein targets can be detected by monitoring changes in surface impedance when a target molecule binds to an immobilized probe. The affinity capture step leads to challenges shared by all label-free affinity biosensors; these challenges are discussed along with others unique to impedance readout. Various possible mechanisms for impedance change upon target binding are discussed. We critically summarize accomplishments of past label-free impedance biosensors and identify areas for future research. [source]

    Red blood cell quantification microfluidic chip using polyelectrolytic gel electrodes

    ELECTROPHORESIS, Issue 9 2009
    Kwang Bok Kim
    Abstract This paper reports on a novel microfluidic chip with polyelectrolytic gel electrodes (PGEs) used to rapidly count the number of red blood cells (RBCs) in diluted whole blood. The proposed microdevice is based on the principle that the impedance across a microchannel between two PGEs varies sensitively as RBCs pass through it. The number and amplitude of impedance peaks provide the information about the number and size of RBCs, respectively. This system features a low-voltage dc detection method and non-contact condition between cells and metal electrodes. Major advantages include stable detection under varying cellular flow rate and position in the microchannel, little chance of cell damage due to high electric field gradient and no surface fouling of the metal electrodes. The performance of this PGEs-based system was evaluated in three steps. First, in order to observe the size-only dependence of the impedance signal, three different sizes of fluorescent microbeads (7.2, 10.0, and 15.0,,m; Bangs laboratories, USA) were used in the experiment. Second, the cell counting performance was evaluated by using 7.2,,m fluorescent microbeads, similar in size to RBCs, in various concentrations and comparing the results with an animal hematoanalyzer (MS 9-5; Melet schloesing laboratories, France). Finally, in human blood sample tests, intravenously collected whole blood was just diluted in a PBS without centrifuge or other pretreatments. The PGE-based system produced almost identical number of RBCs in over 800-fold diluted samples to the results from a commercialized human hematoanalyzer (HST-N402XE; Sysmex, Japan). [source]

    Development of Live Cell Chips to Monitor Cell Differentiation Processes

    C. Maercker
    Abstract A big demand exists for high-throughput functional in vitro assays which can measure cellular phenotypes by molecular methods and therefore improve the resources of primary cells for cell therapy, tissue engineering and high-content screenings in drug development. This approach focuses on cellular adhesion which is an important differentiation process during homing of stem cells. Moreover, it is a promising method especially for adherent cells which are not accessible by classical cell sorting methods. The chip design includes a housing with electrodes to measure electric field densities and impedance, respectively. Moreover, specific coatings of the wells permit a perfect growth of the selected cell types. In parallel, protein biomarkers can be followed by light microscopy. So far, experiments have been started to discriminate between different cell densities and cell types. In addition, after stimulating human cardiac fibroblasts and human umbilical vein endothelial cells, concentrations of proteins involved in adhesion had been increased, and proteins were translocated within the cells. In ongoing experiments, different human cell lines and fibroblastoid mesenchymal stem cells isolated from fat tissue, umbilical cord, or bone marrow are tested in the chip. To optimize the adhesion conditions, the surfaces within the vials of the chip were specifically activated. Microscopy was adjusted to be able to measure cellular morphology in parallel. This concept allows to identify the behavior of mesenchymal stem cells, which cannot be described so far by standard biomarkers. In addition, simulation of the homing process of the cells within its stem cell niche in an in vitro assay is a promising setup for large-scale gain-of-function or loss-of-function screenings in functional genomics as well as for generating precursor cells relevant for the therapy of various diseases. [source]

    Bench to Bedside: Electrophysiologic and Clinical Principles of Noninvasive Hemodynamic Monitoring Using Impedance Cardiography

    Richard L. Summers MD
    Abstract The evaluation of the hemodynamic state of the severely ill patient is a common problem in emergency medicine. While conventional vital signs offer some insight into delineating the circulatory pathophysiology, it is often impossible to determine the true clinical state from an analysis of blood pressure and heart rate alone. Cardiac output measurements by thermodilution have been the criterion standard for the evaluation of hemodynamics. However, this technology is invasive, expensive, time-consuming, and impractical for most emergency department environments. Impedance cardiography (ICG) is a noninvasive method of obtaining continuous measurements of hemodynamic data such as cardiac output that requires little technical expertise. ICG technology was first developed by NASA in the 1960s and is based on the idea that the human thorax is electrically a nonhomogeneous, bulk conductor. Variation in the impedance to flow of a high-frequency, low-magnitude alternating current across the thorax results in the generation of a measured waveform from which stroke volume can be calculated by a modification of the pulse contour method. To adequately judge the possible role of this technology in the practice of emergency medicine, it is important to have a sufficient understanding of the basic scientific principles involved as well as the clinical validity and limitations of the technique. [source]

    Considerations for pacing of the cricoarytenoid dorsalis muscle by neuroprosthesis in horses

    Summary Reasons for performing study: The success rate of prosthetic laryngoplasty is limited and may be associated with significant sequelae. Nerve muscle pedicle transplantation has been attempted but requires a year before function is restored. Objective: To determine the optimal parameters for functional electrical stimulation of the recurrent laryngeal nerve in horses. Methods: An experimental in vivo study was performed on 7 mature horses (2,21 years). A nerve cuff was placed on the distal end of the common trunk of the recurrent laryngeal nerve (RLN). In 6 horses the ipsilateral adductor branch of RLN was also transected. The electrodes were connected to programmable internal stimulator. Stimulation was performed using cathodic phase and then biphasic pulses at 24 Hz with a 0.427 ms pulse duration. Stimulation-response experiments were performed at monthly intervals, from one week following implantation. The study continued until unit failure or the end of project (12 months). Two of the horses were stimulated continuously for 60 min to assess onset of fatigue. Results: Excellent arytenoid cartilage abduction (mean arytenoid angle of 52.7°, range 48.5,56.2°) was obtained in 6 horses (laryngeal grades I or II (n = 3) and III (n = 2). Poor abduction was obtained in grade IV horses (n = 2). Arytenoid abduction was maintained for up to a year in one horse. Technical implant failure resulted in loss of abduction in 6 horses at one week to 11 months post operatively. Mean tissue impedance was 1.06 kOhm (range 0.64,1.67 kOhm) at one week, twice this value at 2 months (mean 2.32, range 1.11,3.75 kOhm) and was stable thereafter. Maximal abduction was achieved at a stimulation range of 0.65,7.2 mA. No electrical leakage was observed. Constant stimulation of the recurrent laryngeal nerve for 60 min led to full abduction without evidence of muscle fatigue. Conclusions: Functional electrical stimulation of the recurrent laryngeal nerve leading to full arytenoid abduction can be achieved. The minimal stimulation amplitude for maximal abduction angle is slightly higher than those for man and dogs. Clinical relevance: This treatment modality could eventually be applicable to horses with recurrent laryngeal neuropathy. [source]

    Aminoguanidine prevents arterial stiffening in a new rat model of type 2 diabetes

    K.-C. Chang
    Abstract Background, Formation of advanced glycation end-products (AGEs) on collagen within the arterial wall may be responsible for the development of diabetic vascular injury. This study focused on investigating the role of aminoguanidine (AG), an inhibitor of AGE formation, in the prevention of noninsulin-dependent diabetes mellitus (NIDDM)-derived arterial stiffening and cardiac hypertrophy in rats. Materials and methods, The NIDDM was induced in male Wistar rats, which were administered intraperitoneally with 180 mg kg,1 nicotinamide (NA) 30 min before an intravenous injection of 50 mg kg,1 streptozotocin (STZ). After induction of diabetes mellitus type 2, animals receiving daily peritoneal injections with 50 mg kg,1 AG for 8 weeks were compared with the age-matched, untreated, diabetic controls. Results, After exposure to AG, the STZ-NA diabetic rats had improved aortic distensibility, as evidenced by 18·8% reduction of aortic characteristic impedance (P < 0·05). Treatment of the experimental syndrome with AG also resulted in a significant increase in wave transit time (+23·7%, P < 0·05) and a decrease in wave reflection factor (,26·6%, P < 0·05), suggesting that AG may prevent the NIDDM-induced augmentation in systolic load of the left ventricle. Also, the glycation-derived modification on aortic collagen was found to be retarded by AG. The diminished ratio of left ventricular weight to body weight suggested that prevention of the diabetes-related cardiac hypertrophy by AG may correspond to the drug-induced decline in aortic stiffening. Conclusions, Long-term administration of AG to the STZ-NA diabetic rats imparts significant protection against the NIDDM-derived impairment in vascular dynamics, at least partly through inhibition of the AGE accumulation on collagen in the arterial wall. [source]

    Arterial stiffening and cardiac hypertrophy in a new rat model of type 2 diabetes

    K.-C. Chang
    Abstract Background, We determined the effects of NIDDM on haemodynamic parameters describing arterial wall elasticity and cardiac hypertrophy in rats administered streptozotocin (STZ) and nicotinamide (NA), using the aortic impedance analysis. Methods, Male Wistar rats at 2 months were administered intraperitoneally 180 mg kg,1 of NA, 30 min before an intravenous injection of 50 mg kg,1 STZ, to induce type 2 diabetes. The STZ-NA rats were divided into two groups, 4 weeks and 8 weeks after induction of diabetes, and compared with untreated age-matched controls. Pulsatile aortic pressure and flow signals were measured by a high-fidelity pressure sensor and electromagnetic flow probe, respectively, and were then subjected to Fourier transformation for the analysis of aortic input impedance. Results, In each diabetic group, the experimental syndrome was characterized by a moderate and stable hyperglycaemia and a relative deficiency of insulin secretion. However, the 8-week but not the 4-week STZ-NA diabetic rats showed a decrease in cardiac output in the absence of any significant changes in mean aortic pressure, having increased total peripheral resistance. The diabetic syndrome at 8 weeks also contributed to an increase in aortic characteristic impedance, from 1·49 ± 0·33 (mean ± SD) to 1·95 ± 0·28 mmHg s mL,1 (P < 0·05), suggesting a detriment to the aortic distensibility in NIDDM. Meanwhile, the STZ-NA diabetic animals after 8 weeks had an increased wave reflection factor (0·46 ± 0·09 vs. 0·61 ± 0·13, P < 0·05) and decreased wave transit time (25·8 ± 3·8 vs. 20·6 ± 2·8 ms, P < 0·05). Ratio of the left ventricular weight to body weight was also enhanced in the 8-week STZ-NA diabetic rats. Conclusion, The heavy intensity with early return of the pulse wave reflection may augment systolic load of the left ventricle coupled to the arterial system, leading to cardiac hypertrophy in the rats at 8 weeks after following STZ and NA administration. [source]

    High-frequency behavior of power inductor windings using an accurate multiconductor transmission line model: input impedance evaluation

    J. A. Brandão Faria
    Abstract This research and tutorial paper is the second part of a work dedicated to the analysis and computation of the electromagnetic behavior of inductor windings operating at high-frequency regimes,a critical issue for very fast transient overvoltage studies. The inductor winding, wound around a ferromagnetic core, containing a total number of N dielectric coated cylindrical turns, is modeled by using a multiconductor transmission line (MTL) approach (proximity effects being accounted) whose constitution and characterization was presented in a former paper. In the present work, we make use of the R, G, L, and C constitutive matrices of the structure in order to develop a modal analysis technique-based formulation aimed at the evaluation of the winding's input impedance in the frequency-domain. Results obtained show that the input impedance critically depends not only on the number of layers of the winding but also, and, more importantly, on the frequency, where resonance phenomena play a key role. Frequency-domain analysis is complemented with simulation results in the time-domain that clearly illustrate how critical and sensitive the system response can be under minute changes of the winding's excitation current. Copyright © 2007 John Wiley & Sons, Ltd. [source]