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Results for “Electric Impedance”

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At least 19 recordsLinked to original sources

PubMed1979

EMG needle electrodes: electrical impedance.

The electrical impedance of samples of stainless-steel monopolar needle electrodes and concentric electrodes from 3 manufacturers were measured in 154mM saline solution using sine-wave excitation at 4 frequencies from 10Hz to 10kHz. Current densities of less than 2.5x10(-5) amp/cm2 were used. Measurements on both needle and fine-wire electrodes were also made in live rats. Linear dimensions of the exposed tips were measured from which the areas of exposure were calculated. Surface areas of the monopolar needles varied between 0.06 and 0.15mm2. Presoaking of the electrodes for 20 minutes in saline solution containing a small concentration of a wetting agent produced a sixfold to twentyfold reduction in impedance. The average impedance magnitudes of the monopolar electrodes ranged from 1.4 megohms (Momega) at 10Hz to 6.6 kolohms (komega at 10kHz. The phase angle of the impedance due to the capacitive component of the needle-electrolyte impedance ranged between -45 and -71 degrees. The reduction in impedance resulting from presoaking and the concomitant reduction in electronic noise would be an advantage in observing lowamplitude potentials.

Animals↗

PubMed1992

Simulation method for cardiac stroke volume estimation by intracardiac electrical impedance measurement.

Using the electrical impedance measurement technique to investigate stroke volume estimation, three models of the ventricle were simulated. A four-electrode impedance catheter was used; two electrodes to set up an electric field in the model and the other two to measure the potential difference. A new approach, itself an application of the quasi-static case of a method used to solve electromagnetic field problems, was used to solve the electric field in the model. The behaviour of the estimation is examined with respect to the electrode configuration on the catheter and to catheter location with respect to the ventricle walls. Cardiac stroke volume estimation was found to be robust to catheter location generating a 10 per cent error for an offset of 40 per cent of the catheter from the chamber axis and rotation of 20 degrees with respect to the axis. The electrode configuration has a dominant effect on the sensitivity and accuracy of the estimation. Certain configurations gave high accuracy, whereas in others high sensitivity was found with lower accuracy. This led to the conclusion that the electrode configuration should be carefully chosen according to the desired criteria.

Electric Impedance↗

PubMed1977

Changes in transthoracic electrical impedance at high altitude.

Mean transthoracic electrical impedance (impedance) which is inversely related to intrathoracic extravascular fluid volume was measured in 121 normal healthy volunteers at sea-level and at 3658 metres altitude. Fifty (group A) reached the high altitude location after an hour's journey in a pressurised aircraft. Twenty-five (group D) underwent slow road ascent including acclimatisation en route. Thirty permanent residents (group B) and 16 temporary residents at high altitude (group C) were also studied. Serial studies in the 30 subjects of group A who developed symptoms of high altidue sickness showed a significant decrease of impedance up to the fourth day of exposure to high altitude which later returned to normal. The 4 volunteers who developed severe symptoms showed the largest drop in impedance. A case of acute pulmonary oedema developing at 4300 metres showed an impedance value of 24-1 ohms on admission. After effective treatment the impedance increased by 11-9 to 36-0 ohms. Twenty asymptomatic subjects of group A and 25 of group D showed a small average increase in impedance values at high altitude. These obstructions suggest that measurement of transthoracic electrical impedance may be a valuable means of detecting incipient high altitude pulmonary oedema.

Acclimatization↗

PubMed1975

Measurement of pleural effusion by electrical impedance.

Changes in the electrical impedance of the thorax were recorded from various electrode arrays on the thorax during the infusion and withdrawal of saline, plasma, or blood from the right, left, or both hemithoraxes. Impedance changes correlated linearly with the volume of infused fluid. The resistivity of the infused fluid significantly affected the sensitivity (omega/ml) of the impedance method in detecting specific fluid accumulations. The use of hemithoracic electrode arrays permitted the localization of fluid accumulations to a specific hemithorax. Various factors that can alter the magnitude and interpretation of impedance changes are discussed, as they would affect the clinical interpretation of impedance changes, particularly in postoperative patients.

Animals↗

PubMed1977

Electrical impedance measurements in the reading and monitoring of broth dilution susceptibility tests.

Electrical impedance changes in the medium were studied during traditional broth dilution tests. Tests involved clinical isolates of Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, Enterobacter sp., Klebsiella, and enterococcus and ten antibiotics. Minimal inhibitory concentration (MIC) values from overnight visual readings were compared with MIC values determined from electrical impedance end points, using inocula of 10(6) organisms per ml. Ninety-three percent of the results were within one twofold dilution of each other. When the impedance end point was determined at 6 h, this correlation was lowered to 34%. By increasing the initial electrical impedance inoculum 10-fold, the correlation between the 6-h impedance MIC and the overnight visual MIC was improved to 74%. Ampicillin, tetracycline, and polymyxin E results accounted for most discrepancies. Continuous monitoring of impedance changes suggested that better correspondence could be obtained by adjusting the end point criteria for the 6-h impedance MIC with different antibiotics. Electrical impedance methods for reading bacterial end points in automated clinical laboratory instruments appear promising.

Culture Media↗

PubMed1977

Detection of bacteriuria by automated electrical impedance monitoring in a clinical microbiology laboratory.

An apparatus capable of rapidly detecting changes in electrical impedance was utilized for the continuous monitoring of bacterial growth in routine urine specimens in a clinical laboratory. In a trial study, 200 clinical specimens analyzed by the electrical impedance method resulted in an average detection time of 2.5 h for 41 clinically significant specimens, whereas conventional methods for bacterial isolation required overnight culture. Those specimens positive by the electrical impedance monitoring but negative by conventional bacteriological methods accounted for less than 2% of the total number of positive specimens, whereas electrical impedance-negative but conventional culture-positive specimens accounted for ca. 4%. Electrical impedance apparatus in clinical microbiology laboratories could provide rapid screening of clinical urine specimens as well as accurate detection of bacterial growth.

Bacteria↗

PubMed1977

Rapid detection of bacterial growth in blood samples by a continuous-monitoring electrical impedance apparatus.

A growth detection method utilizing an automated apparatus capable of rapidly detecting bacterial growth by measuring changes of electrical impedance in bacteriological medium was utilized with "mock" blood cultures containing various gram-negative and gram-positive bacteria. Measurement of changes of electrical impedance was found to ba as accurate and comparable for time of growth detection as the radiometric method for detection of the same bacteria using mock blood cultures. In a limited clinical trial the use of the electrical impedance apparatus detected in 1 positive specimen from 40 clinical blood specimens as rapidly as by radiometric measurement. Both methods were considerably faster for detecting bacterial growth as compared with conventional culture methods. The selected species of gram-positive and -negative organisms tested were all detected by the electrical impedance method, including aerobes and anerobes. However, addition of 5% CO2 to the incubation atmosphere enhanced detection of gram-positive organisms.

Aerobiosis↗

PubMed1977

[Relationship between the renal electrical impedance variations with glomerular filtration rate changes in dogs (author's transl)].

Records of the electrical impedance were obtained by means of surface electrodes placed on ventral and dorsal sides of the left kidney of anesthetized dogs. Changes of the renal electrical impedance resulted from alterations of the glomerular filtration rate caused by decrease of blood renal pressure to 80 and 50 mm Hg either due to constriction of the aorta or bleeding. The relation were established also by using physiological solution's infusion. The results showed that changes of the means of renal electrical impedance were in opposite direction to changes in glomerular filtration rate. The electrodes employed were constituted of two parts: one fixed and another adjustable and flexible, possibiliting a good contact with the renal surface independently of the kidney size.

Animals↗

PubMed1992

Electrical impedance applied to non-invasive detection of irritation in skin.

Healthy volunteers were subjected to irritation by sodium lauryl sulphate at concentrations in the range 0.002% to 5.0% applied in Finn Chambers for 24 h. Test sites were visually assessed 1 h and 24 h after cessation of exposure. At the same times electrical impedance was measured with a new impedance device which allows non-invasive local measurements to a controlled depth. Close agreement between concentration and an irritation index calculated from electrical impedance parameters was found over the whole concentration range for most test persons. At concentrations below 0.2%, visual scores were zero. These results suggest that electrical impedance can be used as an objective tool to record irritation, and further that electrical impedance might be a more sensitive method than the commonly used visual readings.

Adolescent↗

PubMed1979

Automated electrical impedance technique for rapid enumeration of fecal coliforms in effluents from sewage treatment plants.

Fecal coliforms growing in a selective lactose-based broth medium at 44.5 degrees C generate a change in the electrical impedance of the culture relative to a sterile control when populations reach 10(6) to 10(7) per ml. The ratio of these changes was measured automatically, and the data were processed by computer. A linear relation was found between the log10 of the number of fecal coliforms in an inoculum and the time required for an electrical impedance ratio signal to be detected. Pure culture inocula consisting of 100 fecal coliforms in log phase or stationary phase were detected in 6.5 and 7.7 h, respectively. Standard curves of log10 fecal coliforms in wastewater inocula versus detection time, based on samples collected at a sewage treatment plant over a 4-month period, were found to vary from one another with time. Nevertheless, detection times were rapid and ranged from 5.8 to 7.9 h for 200 fecal coliforms to 8.7 to 11.4 h for 1 fecal coliform. Variations in detection times for a given number of fecal coliforms were also found among sewage treatment plants. A strategy is proposed which takes these variations into account and allows for rapid, automated enumeration of fecal coliforms in wastewater by the electrical impedance ratio technique.

Bacteriological Techniques↗

PubMed1992

How reliable is bio-electrical impedance analysis for individual patients?

We performed bio-electrical impedance analysis (BIA) on 38 healthy adults with an initial body mass index (+/- s.d.) of 30 kg/m2 (+/- 5) before and after a low calorie diet. Five weeks later a mean weight loss of 4.2 +/- 2.3 kg was observed. According to BIA, fat-free mass (FFM) decreased in 28 subjects and increased in ten. In four cases the reduction was greater than the weight loss. At the end of the ten week diet regimen all 27 subjects followed up demonstrated a further weight reduction. According to BIA, FFM decreased in 22 subjects, increased in four and did not change in one case. In one case the reduction was greater than the weight loss. Although mean FFM values assessed by skinfolds and BIA were not significantly different before and after the weight loss period, no correlations were found among the individual changes in FFM evaluated by the two methods. Our results suggest that single frequency (50 KHz) impedance must be used with care in clinical conditions.

Adult↗

PubMed1976

Pulsatile changes of electrical impedance in the lower limb.

The ratio of the pulsatile and the mean value of the volume of blood flowing through the calves of normal subjects with each heart beat was calculated from electrical impedance changes during venous occlusion plethysmography. Measurements made concurrently by proven Doppler ultrasound techniques did not correlate with ratios derived from the impedance measurements. The pulsatile change in electrical impedance in the limbs appears to be due more to changes of resistance in the blood than to pulsatile changes in the volume of the limb.

Adolescent↗

PubMedDate not supplied

Clinical application of electrical impedance for the study of arterial insufficiency.

A four-electrode impedance plethysmography containing a dedicated computer has been developed for evaluating arterial insufficiency in the clinical noninvasive vascular laboratory. Measurements obtained by the impedance plethysmograph were compared with measurements obtained by the Doppler ultrasound technique. Five case reports demonstrate that electrical impedance measurements can feasibly be obtained in the clinical setting and that the information is useful in treating patients with arterial insufficiency. Results indicate that electrical impedance data correlate better with the clinical symptoms reported by the patient than do the Doppler systolic pressure data. The impedance plethysmography measurements are particularly useful when considered in conjunction with the Doppler measurements.

Adult↗

PubMed1979

Intrathoracic electrical impedance measurements from an esophageal probe.

The sensing of intrathoracic electrical impedance from an esophageal probe may allow relatively noninvasive monitoring of cardiac and respiratory functions of particular interest in anesthesia and intensive care. We have obtained a partial solution of the intrathoracic current-field problem for impedance measurements made from a four-terminal linear array of electrodes located in the esophagus. It allows prediction that aortic root motion will exceed aortic distension as a major determinant of the cardiac intrathoracic esophageal impedance signal. This prediction was confirmed for a specific carefully selected and placed electrode array in anesthetized dogs. In general, motions of organs will be more important than volume changes in affecting the esophageal impedance signal. Thus, timing information (preejection period and left ventricular ejection time) is available from electrodes on an esophageal probe, but cardiac output information appears to be inaccessible for fundamental reasons.

Cardiography, Impedance↗

PubMedDate not supplied

Electrical impedance as a locating method in human stereotactic surgery.

During stereotactic surgery, electrical impedance was measured by means of a roving electrode technique with a sine wave current of 10 kc. Impedance showed a characteristic decrease when the electrode was passing through the thalamus and consequently the impedance profile corresponding to the thalamic area exhibited the characteristic shape of a 'frying pan'. By observing the impedance, it is possible to differentiate the thalamic gray matter from the surrounding structures with some accuracy.

Animals↗

PubMed2026

Respiratory effects of recruitment maneuvers according to lung recruitability assessed by electrical impedance tomography in patients with acute respiratory distress syndrome.

Recruitment maneuvers (RM) can improve oxygenation in patients with acute respiratory distress syndrome (ARDS), but their physiological effects depend on lung recruitability. This secondary analysis of a randomized controlled trial (RCT) evaluated oxygenation, respiratory mechanics, regional ventilation, and cardiorespiratory adverse events responses to a RM followed by electrical impedance tomography (EIT)-guided PEEP titration, using EIT to assess lung recruitability. In this study, fifty patients with moderate-to-severe ARDS underwent a stepwise RM followed by individualized PEEP titration guided by EIT. Lung recruitability was determined using the collapse index at PEEP 6 cmH₂O (CLPEEP6), defined as the proportion of collapsed lung at this PEEP level. Patients were classified into high- and low-recruitability groups based on median CLPEEP6 values. Oxygenation (PaO₂/FiO₂), static compliance (Cstat), driving pressure (Pdriv), regional ventilation distribution, and cardiorespiratory adverse events were compared before and after RM, during subsequent individualized EIT-guided PEEP titration. In patients with high recruitability (CLPEEP6 > 12.5), the PaO₂/FiO₂ ratio and Cstat increased significantly after RM (PaO₂/FiO₂: 100.8 ± 30.3 vs. 125.4 ± 38.3 mmHg, p < 0.05; Cstat: 21.5 ± 5.8 vs. 28.0 ± 7.0 mL/cmH₂O, p < 0.001), Pdriv decreased (19.1 ± 3.5 vs. 15.6 ± 3.2 cmH₂O, p < 0.001). EIT demonstrated a posterior redistribution of ventilation after RM. In contrast, patients with low recruitability (CLPEEP6 ≤ 12.5) showed no significant mechanical or oxygenation improvement and transient hypotension, arrhythmia, and desaturation appeared numerically more common in this group. No barotrauma or cardiac arrest occurred, and ICU mortality was similar between groups. A strategy combining a RM with subsequent individualized EIT-guided PEEP titration was associated with improved oxygenation and lung mechanics in patients with high lung recruitability, whereas patients with low recruitability showed limited physiological benefit, with cardiorespiratory adverse events appearing numerically more frequent. The EIT-derived CLPEEP6 index represents a feasible and clinically applicable https://clinicaltrials.gov/study/NCT06733168.

Humans↗

PubMed1975

[Measurement of electric impedance as a screening method for diagnosing haemorrhagic diatheses (author's transl)].

Changes in electrical impedance during blood clotting have been previously described. Personal measurements on blood of 18 healthy donors and 29 patients with various disorders of clotting gave reproducible results with this method. There was a marked difference between normal subjects and those with bleeding diatheses regardless of type. There was good correlation between impedance changes and the thrombelastogram, the former being more sensitive in diagnosing haemorrhagic disorders. Further studies are required to evaluate its place as a screening method in these conditions.

Blood Coagulation Disorders↗

PubMed1992

Comparison of two approaches to measurement of electrical impedance of glass microelectrodes designed for evaluation of temperature changes in biological tissues.

We proposed a temperature sensitive microelectrode for rapid measurements of temperature at the cellular level. In principle, the electrical impedance of the tip of the microelectrode changes with temperature. We designed an impulse measurement system (STEP) sensitive to the above changes of impedance. The system is based on a presettable negative input impedance of the current to a voltage converter. We compared the efficiency of the new STEP with the currently used RAMP system. We found following advantages of the STEP system: i) the danger of high voltage oscillations which could mechanically destroy the microelectrode tip is eliminated; ii) this system provides the opportunity to set the maximum sensitivity of the system according to the measured temperature interval. Moreover, the STEP method makes it possible to measure the resistance by using a sinusoidal stimulation signal which has to be preliminarily compensated by a rectangular signal. The shortest sampling period of the new system represents 0.1 ms with a resolution higher than 0.1 K and sensitivity better than 30 mV/K.

Animals↗