Continuous Impedance Measurement Research Articles

Real‐time measurement of electrode impedance during intracochlear electrode insertion

This pilot study details the use of a software tool that uses continuous impedance measurement during electrode insertion, with the eventual potential to assess and optimize electrode position and reduce insertional trauma. Software development and experimental study with human cadaveric cochleae and two live surgeries. A prototype program to measure intracochlear electrode impedance and display it graphically in real time has been developed. The software was evaluated in human cadaveric temporal bones while simultaneously making real-time fluoroscopic recordings and in two live surgeries during intracochlear electrode insertion. Impedance changes were observed with various scalar positions, and values were consistent with those obtained using clinically available software. Using Contour Advance electrodes, impedance values increased after stylet removal, particularly when using the monopolar mode. Impedance values seem systematically affected by electrode position, with higher values being associated with proximity to the cochlear wall. The new software is capable of acquiring impedance measurements during electrode insertion, and these data may be useful to guide surgeons to achieve optimal and atraumatic electrode insertion, to guide robotic electrode insertion, and to provide insights about electrode position in the cochlea.

Detection of inadvertent catheter movement into the coronary sinus ostium or middle cardiac vein by real-time impedance monitoring prior to radiofrequency ablation in the right atrial posteroseptal region

The objective of this study was to evaluate the use of continuous catheter impedance monitoring prior to ablation to facilitate differentiation of the coronary sinus ostium (CSO) and the middle cardiac vein (MCV) from the right atrial posteroseptal region (RPS). Empiric observations have suggested that continuous catheter impedance monitoring could differentiate the CSO and MCV from the RPS region. Radiofrequency ablation in the MCV or coronary sinus has been associated with coronary artery injury. Differentiation of these areas may be difficult with either fluoroscopy or electrogram characteristics. Continuous impedance measurements using a 4-mm Navistar (Biosense Webster) ablation catheter were conducted in 17 consecutive patients undergoing ablation for supraventricular tachycardia. The average impedance value was recorded at the right atrial septum (RS) posterior to the bundle of His, the RPS region, within 1 cm inside the CSO and in the MCV. These areas were confirmed and demarcated with 3-D mapping and biplane fluoroscopy. A significant increase in impedance was observed between the CSO (X = 146.6 ± 24.8) and RPS [Formula: see text] regions (p < 0.001). Furthermore, a significant rise in impedance was seen between the MCV [Formula: see text] and RPS and CSO, respectively (p < 0.001). No significant change in impedance was found between the RS [Formula: see text] and RPS regions. Continuous impedance measurements during mapping can facilitate differentiation of catheter locations inside the CSO and MCV from extracoronary sinus regions. This may reduce the risk of inadvertent coronary artery damage during the ablation procedure.

Pressure Regulating Ear Plug Testing in a Pressure Chamber

Middle ear barotrauma is a condition frequently associated with flying. It is usually caused by Eustachian tube (ET) dysfunction. Pressure-regulating earplugs (PREP) should improve complaints due to pressure equalization problems. There were 21 patients with a history of pressure equalization problems while flying who were examined. ET function was measured with exploratory tests and in a pressure chamber. In a double-blind study, PREP were examined using continuous impedance measurement in the pressure chamber. Eardrum deflection and pressure-equalizing maneuvers were also examined. During pressure exposure the subjective state of patients with and without PREP was compared. Evidence of ET dysfunction was found in twice as many patients with the impedance method in a pressure chamber compared to tympanometry or the Valsalva test. Use of PREP reduced the rate of pressure changes in the external auditory canal. Maximum pressure was reached with a delay of about 7 min. The number of pressure-equalizing maneuvers did not differ significantly. Using PREP the patients reported a significantly better subjective state on the VAS scale of 2.19 +/- 1.50 compared to 3.38 +/- 2.33 without PREP. Continuous impedance measurements in the pressure chamber identified ET dysfunction more often than the exploratory ET function tests commonly used in routine diagnostics. This novel finding requires further validation. Although use of PREP showed no signs of improving ET function, it did significantly improve individual subjective state during sudden pressure changes.

The endovenous RFITT-treatment of varicose veins, a new method of interventional phlebology

SummaryEndovenous bipolar RFITT (RadioFrequency-Induced ThermoTherapy) is a new approach for the treatment of chronic venous insufficiency. During treatment with RFITT (also known as the Celon method) a thermal effect on the vein walls is applied thanks to bipolar energy delivery. An alternating high frequency current creates heat in the vessel enabling a controlled tissue shrinkage. A continuous impedance measurement allows the controlled heat exposure on the vein wall. An acoustic signal guides the physician during the RFITT application. The Celon power control unit turns off automatically when the desired treatment result is achieved. Patients, method: In our clinic we have used the Celon method from October 9, 2007 through October 10, 2008 for the treatment of 331 varicose veins in 199 patients. 78% of these treatments were applied in the Vena saphena magna (VSM) whereas 22% concerned the Vena saphena parva (VSP). We have treated more than one large varicose vein simultaneously in 117 cases. In 31 varicose veins, which had been treated with laser and became recurrent again, we applied RFITT and were able to occlude the vein permanently. Results: In our patient population we achieved an occlusion rate of 97.6% at 12 months follow up. Five cases in the VSM and three cases in the VSP were recurrencies. We think that this – following to the guidance of the company – was caused by pulling back the RFITT applicator too fast in the vein (application time: 1.2–1.5 s/cm) and with an excessive energy amount of 20–22 W. Meanwhile, we have adapted our technique to a slower mode (18 W, application time 3.4 s/cm) and are achieving significantly better results. Conclusion: We are convinced that we have now found the optimal energy amount and pull-back speed.

Integration of Automatic Intrathoracic Fluid Content Measurement into Clinical Decision Making in Patients with Congestive Heart Failure

Hospitalizations due to decompensation are a frequent problem in treating patients with congestive heart failure (CHF). Continuous impedance measurement via implantable devices may detect pulmonary fluid accumulation due to worsening CHF. An acoustic alert might allow an earlier treatment of impending decompensation. An algorithm that implemented impedance measurement into clinical decision making in treating CHF patients was evaluated. Forty-two CHF patients (ejection fraction: 27 +/- 6%; New York Heart Association 2.9 +/- 0.6) with cardiac resynchronization therapy and automatic impedance measurements were included. Upon an alert, a stepped therapy was initiated: category (1) overt decompensation, hospitalization; category (2) worsened CHF, increase of diuretics; category (3) no CHF worsening, brain natriuretic peptide (BNP) measurement, elevated BNP: increase of diuretics, normal BNP: no specific treatment. During 18 +/- 4 months, 45 alerts were treated according to the algorithm. Eleven category 1 alerts led to hospitalization; 21 category 2 and 11 category 3 patients (elevated BNP) were treated conservatively. Two category 3 alerts (normal BNP) received no treatment. Automatic impedance measurement can be integrated into CHF management. BNP measurement restricted to patients with alert but without clinical signs of worsened CHF may prevent premature therapy escalation.

Awareness and the EEG power spectrum: analysis of frequencies

Power spectral analysis is a well-established method for the analysis of EEG signals. Spectral parameters can be used to quantify pharmacological effects of anaesthetics on the brain and the level of sedation. This method, in numerous variations, has been applied to depth of anaesthesia monitoring and has been incorporated into several commercially available EEG monitors. Because of the importance of EEG spectral analysis, we evaluated the performance of each frequency in the power spectrum regarding detection of awareness. Ninety artefact-free EEG segments of length 8 s were obtained from a database that contains perioperatively recorded EEG data. For the present analysis, EEG data were selected from 39 patients with propofol-remifentanil or sevoflurane-remifentanil anaesthesia with a period of awareness. Half of the EEG segments were recorded during periods of awareness as defined by an adequate response to the command 'squeeze my hand'. The other half were from unresponsive patients. The power spectral density was calculated for each segment. The performance of each frequency bin of the power spectrum as a detector of awareness was assessed with a remapped prediction probability rPK, i.e. the prediction probability PK mapped to a range of 0.5-1. The remapped prediction probability was high (rPK>0.8) for low frequencies (<15 Hz) and for high frequencies (>26 Hz), with a minimum (rPK<0.55) at 21 Hz. Indentations in the 'performance spectrum' occur at the power-line frequency (50 Hz) and its harmonics and at 78 Hz, probably caused by the continuous impedance measurement of another device used in parallel. With the exception of the indentations, the remapped prediction probability of the high frequencies (>35 Hz) was >0.95. The best performance for the detection of awareness was achieved by EEG power spectral frequencies from >35 Hz up to 127 Hz. This frequency band may be dominated by muscle activity. The frequency band between 15 and 26 Hz may be of limited value, as reflected by lower rPK values.

Continuous Detection of Volatile Aromatic, Unsaturated or Halogenated Hydrocarbons in Air by Adsorption on Pt-Electrodes and Subsequent Oxidative Desorption

Many organic compounds such as benzene, its derivatives and simple halogenated hydrocarbons cannot be detected by usual amperometric sensors. Their detection, however, is possible by means of their adsorption at a Pt-sensor electrode. The charge is automatically determined during a subsequent sweep to potentials above 1 V (RHE). It is corrected for oxygen adsorption and serves as a measure for the substance concentration. A special potential program serves to repeatedly strip the adsorbate from the surface, thus allowing the continuous detection of such compounds [1]. By a continuous impedance measurement, the amount of adsorbate is monitored during the adsorption period. In this way, the adsorption period is finished at a preset, constant coverage and a linear dependence on concentration is obtained. Some examples for cross sensitivities are given, as well as ways to reduce them by using appropriate potential programs. A negligible cross sensitivity of a toluene sensor towards CO (<3.5×10−3, toluene=1) is demonstrated, which is important for the detection of BTX compounds in traffic.

Detection of hydrocarbons in air by adsorption on Pt-electrodes using continuous impedance measurements

In this paper, it is shown that the detection of many organic compounds such as benzene, its derivatives and simple halogenated hydrocarbons is possible by means of their adsorption at a Pt-sensor electrode. The change of electrode capacity due to adsorbate formation is continuously monitored by ac measurements. This is possible despite the high oxygen reduction currents at the adsorption potentials. A special potential program serves to repeatedly strip the adsorbate from the surface, thus allowing the continuous detection of such compounds with sensitivities in the low ppm range.

Monosialoganglioside GM1 treatment after a hypoxic-ischemic episode reduces the vulnerability of the fetal sheep brain to subsequent injuries

OBJECTIVE: A transient hypoxic-ischemic episode can markedly sensitize regions of the fetal brain, particularly the striatum, to further insults occurring in close succession. The purpose of this study was to determine whether ganglioside GM1 given to the fetus after a hypoxic-ischemic episode can counteract this sensitization and protect against subsequent insults. STUDY DESIGN: Chronically instrumented near-term fetal sheep (119 to 133 days) were subjected to three 10-minute episodes of reversible cerebral ischemia at 1-hour intervals. Six were given 30 mg/kg ganglioside GM1 through the umbilical vein, commencing immediately after the release of the occluder, over the next 2 hours, followed by a continuous infusion of 30 mg/kg/day over 60 hours after ischemia; these were compared with seven vehicle-treated controls. The time course of electrocorticographic activity and cytotoxic edema within the parasagittal cortex were determined with real-time spectral analysis and continuous impedance measurements, respectively. The degree and distribution of neuronal death was assessed histologically 72 hours later. RESULTS: Ganglioside GM1 improved recovery of primary edema and markedly reduced histologic damage (p < 0.001), particularly in the striatum, hippocampus, and cortex. At 72 hours after ischemia electrocorticographic activity had returned to normal in the ganglioside GM1 - treated group but was still depressed (p < 0.001) in the control group. CONCLUSION: These results showed that ganglioside GM1 treatment initiated immediately after a transient hypoxic-ischemic episode stabilized membrane function and markedly improved neuronal outcome after subsequent insults, suggesting its potential therapeutic value in acute situations of repeated hypoxia-ischemia in the perinatal period. (AM J OBSTET GYNECOL 1994;170:663-70.)

GM1 ganglioside given after hypoxia-ischaemia markedly protects the fetal sheep brain from subsequent injuries

The purpose of this study was to determine whether GM1 given to the fetus after a hypoxic-ischaemic episode can protect the fetal brain against subsequent insults. Chronically instrumented near-term fetal sheep were subjected to three 10-minute episodes of reversible cerebral ischaemia, repeated at 1 hour apart. Six were given 30 mg/kg of GM1 through the umbilical vein at the end of the first ischaemia for the next 2 hours followed by a continuous infusion of 30 mg/kg/day over 60 hours after ischaemia: these were compared with 7 vehicle-treated controls. The time course of electrocorticographic (ECoG) activity and cytotoxic oedema within the parasagittal cortex were determined with real-time spectral analysis and continuous impedance measurements respectively. GM1 improved recovery of primary oedema and markedly reduced histologic damage (p < 0.001) particularly in the striatum, hippocampus and cortex. At 72 hours after ischaemia, ECoG activity had returned to normal in the GMl-treated group but was still depressed (p < 0.001) in the control group. These results showed that GM1 treatment initialed immediately after a transient hypoxic-ischaemic episode stabilised membrane function and markedly improved neuronal outcome following subsequent insults suggesting its potential therapeutic value in situations of repeated hypoxia-ischaemia in the perinatal period.

Pretreatment with monosialoganglioside GM1 protects the brain of fetal sheep against hypoxic-ischemic injury without causing systemic compromise.

The purpose of this study was to determine whether prophylaxis with monosialoganglioside GM1 can protect the fetus from hypoxic-ischemic encephalopathy in utero. Because some protective strategies can compromise the fetus, the effect of GM1 treatment on metabolic status and blood pressure was also evaluated. Chronically instrumented near-term fetal sheep (119-133 d) were subjected to 30 min of severe cerebral ischemia. Six were given 30 mg/kg GM1 through the umbilical vein 2 h before insult followed by continuous infusion of 30 mg/kg/d over the next 60 h, and these were compared with seven vehicle-treated control sheep. The time course of electrocorticographic activity and cytotoxic edema within the parasagittal cortex were determined with real-time spectral analysis and continuous impedance measurements, respectively. Histologic outcome was assessed 72 h later. Pretreatment with GM1 improved recovery of primary edema, reduced the duration of epileptiform activity (15 +/- 2 versus 31 +/- 5 h; p < 0.05) and the magnitude of secondary edema (p < 0.05). At 72 h, histologic damage was reduced, particularly in the cortex (p < 0.05) and hippocampus (p < 0.01), and residual electrocorticographic activity was increased in the GM1-treated group (-5 +/- 1 versus -9 +/- 3 dB, p < 0.01). GM1 infusion did not alter arterial blood pressure or metabolic status. These results indicate that GM1 can protect the fetal brain against hypoxic-ischemic injury without causing hypotension or metabolic compromise.

Sealing of Porous Anodic Films on Aluminium

SummaryThe sealing of porous anodic films, formed on aluminium in sulphuric acid, has been examined using electrochemical impedance spectroscopy. In contrast to many previous studies, distilled water has been used, and measurements have been made both at room temperature and at the boiling point of water. The latter approach has formed the basis of the assessment of impedance spectroscopy as an on-line monitoring technique for the effectiveness of sealing of porous anodic films on aluminium.Studies using interruption of the seating process have revealed the importance of pore hydration resistance in determining the extent of sealing after the bridging or plugging over of the pore mouths. This has led to a refinement of the basic equivalent circuit of sealed anodic films. For continuous impedance measurements at the sealing temperature, a further modification of the equivalent circuit is necessary to allow simulation of the impedance response. The modified response indicates the importance of gel-like mate...

Corrosion of Alloy 600 by Cationic Resin Beads

Several instances of corrosion and stress corrosion cracking in light water reactor coolants have been attributed to the incidental presence of ion exchange resin in the coolant. Tests performed in high temperature water slurries of cation exchange resins have shown preferential pitting and general attack of Alloy 600. Continuous ac impedance measurements were performed to monitor the corrosion during the test. The frequency dependence of the ac impedance allows separation of the resistance of the corroding interface from the resistance of the slurry. The results have been shown that attack commences at relatively low temperatures near 80°C, increases with increasing temperature up to 289°C, and slows with decomposition of the resin held at 289°C. Postmortem analysis showed hemispherical pitting under partially decomposed beads, surrounded by a scale enriched in chromium and sulfur.

Electrical impedance measurements: rapid method for detecting and monitoring microorganisms

A conceptually simple and east-to-use technique is described that uses continuous impedance measurements for automated monitoring of microbial growth and metabolism. The method has been applied to a wide range of microorganisms. Optical clarity is not required. The sensitivity and reproducibility of the method are demonstrated. The mechanism whereby microbial growth alters the impedance of the medium is discussed, as well as potential applications of the method to clinical microbiology.