Significant Increase In Impedance Research Articles

Conducting Polymers and Corrosion: Part 2 — Polyaniline on Aluminum Alloys

Abstract The electrochemical behavior of conducting polyaniline coatings on various aluminum alloys subjected to immersion in dilute Harrison solution (0.35% ammonium sulfate [(NH4)2SO4], 0.05% sodium chloride [NaCl]) was studied. Electrochemical impedance spectroscopy revealed that the charge-transfer resistance (Rct) of polyaniline-coated alloys increased as a function of immersion time. Polyaniline-coated platinum did not exhibit a significant increase in impedance under similar conditions, indicating that an active metal in contact with the polyaniline is required for the observed increase in Rct. A similar pattern of increasing Rct was observed for Alodine (Product A)-treated Al 7075T-6 (UNS A97075) alloys. Mean current and mean potential values obtained from electrochemical noise measurements also suggest a substantial electrochemical interaction between the polyaniline and the aluminum alloy during the early stages of immersion. Polarization experiments and opencircuit potential measurements reveal...

Intramyocardial Impedance Measurements for Diagnosis of Acute Cardiac Allograft Rejection

Abstract Background . Measurements of intramyocardial impedance at high frequencies can indicate alterations in cell membranes and intracellular spaces during acute cardiac allograft rejection. Methods . Fifteen beagle dogs underwent heterotopic heart transplantation and were immunosuppressed with cyclosporine and methyl prednisolone (MP). Impedance was determined twice daily by means of four screw-in electrodes in the right and left ventricle. Transmyocardial biopsies and the intramyocardial electrogram (IMEG) were performed as reference methods. A total of 23 rejection episodes were induced. When acute rejection was recognized histologically and through IMEG readings, the animals were treated with a bolus of 125 mg of methyl prednisolone over 5 consecutive days. Treatment of rejection was controlled by biopsy and IMEG. Results . All hearts showed a uniform decrease in impedance of about 28.3% ± 5.5% immediately after transplantation, which subsequently reached a stable plateau after 7 to 8 days. Impedance values then remained unchanged as long as rejection was absent. Biopsy findings of grades 1A to 1B (ISHLT) were accompanied by a statistically significant increase in impedance of 12.2% ± 2.5%; of grades 2 to 3A of 19.2% ± 3.2% and of grades 3B to 4 of 27.0% ± 2.9%. Sensitivity was 96%, specificity 91%. Successful treatment of rejection led to a decrease of impedance to the initial levels. Conclusions . The amount of increase in impedance of high frequencies is a method to stratify acute cardiac allograft rejection into grades like histologically grading. The effectiveness of rejection treatment can also be monitored through impedance measurement. The method is also applicable for telemetric rejection monitoring by means of an implantable device.

Changes in the Electrical Impedance of Blood during Coagulation

REPORTS on the impedance changes of blood during coagulation have been conflicting, and many have concluded that there is no significant impedance change which could be related to the coagulation process1–5. In 1948, however, Rosenthal and Tobias6, using improved techniques, demonstrated a significant increase in impedance following coagulation, but the technique never came into practical use. Moreover, though some workers confirmed the observations7, others claimed to obtain conficting results8.