An implantable telemetry system for continuous chronic monitoring of kidney oxygenation in freely moving rats

Abstract

We present a telemetry system for long-term monitoring of in-vivo kidney tissue oxygen. The transmitter contains an embedded potentiostat and has an attached carbon-paste electrode for amperometric detection of dissolved O2 (electrode diameter 200μm, transmitter wt 11 gm). Each electrode responds to physiological concentrations of O2 (50–80μM). The O</sub> concentration of the tissue is converted to an electrical current by the reduction of O2 on the carbon-paste. The total RMS noise of the telemetry system was 0.23μM. Inductive power transfer is utilised to recharge the telemeter transcutaneously, thus maintaining continuous recording for potentially the lifetime of the animal. In anesthetised rats the system was validated against a Clark-type electrode (50μm tip) and both electrodes were simultaneously inserted into the kidney. Rats were ventilated with different O2 concentrations to vary the kidney oxygen tension, and measurements were made at increasing depths in the tissue. The renal tissue oxygen tension measurements by these two methods were correlated (r2=0.466; p<0.001), with no fixed or proportional bias. Electrodes were also chronically implanted in the kidney. In conscious rats, the inspired O2 concentration was varied (10%, 21%, 100%). The observed renal oxygen tension agreed with changes in inspired O2 concentration. The implanted system was shown to be stable for >5 weeks.