Biomedical subjects

W Lager

Publications and source records attributed to W Lager.

6 recordsLinked to original sources

PubMed1994

Electrocatalytic glucose sensor.

An electrocatalytic glucose sensor for in vivo application has been developed. The sensor is a flow-through cell with three electrodes and can be integrated into a blood vessel. The principle of measurement is based on the direct electrochemical oxidation of glucose at a membrane-covered noble-metal electrode. To test the potential long-term in vivo function of the sensor, it was implanted in the carotid artery of a sheep. Thus, the sensor performance was verified over a period of 71 days. During this time, a nearly constant blood flow through the cell was achieved, which indicates good blood compatibility of the materials used. It was possible to set up a calibration that was valid over 24 days (mean error 2.3 mmol l-1). The tested cross-sensitivity of the sensor towards cysteine, acetyl salicylic acid and other small molecules shows tolerable effects on this type of glucose measurement. Only high concentrations of lactate and ethanol require a special adaptation of the calibration to suppress their influence. Minor cross-sensitivity and promising long-term stability recommend this type of sensor for in vivo monitoring of blood sugar level. However, for intravasal application, it is necessary to modify the present sensor design to a catheter-type construction.

Animals↗

PubMed1994

Implantable electrocatalytic glucose sensor.

An electrocatalytic glucose sensor for in vivo application has been developed to determine the glucose level in blood and further to control the insulin dosage in a closed loop system for diabetes therapy. The principle of the electrocatalytic glucose sensor is based on the direct electrochemical oxidation of glucose at a membrane-covered platinum electrode. For a possible clinical application the sensor was built as a catheter. A set of implantations in the vena cava of sheep demonstrated the potential feasibility of the sensor. The sensor values were simultaneously checked by the enzymatic analysis of glucose in blood samples drawn separately from a femoral vein. It was possible to determine the glucose concentration in sheep for more than 130 days with tolerable deviations from glucose reference measurements. The mean error was 2.5 mmol/l. One of the catheters was explanted after 211 days and the histological examination revealed a good biocompatibility of all materials used. In additional experiments, the differences of the glucose concentration in vena cava as well as in the anterior and posterior femoral veins of a sheep were examined during glucose tolerance tests. These experiments verified our method of in vivo calibration of the long-term implantable glucose sensor.

Animals↗

PubMed1994

Electrocatalytic glucose sensor for long-term in vivo use.

A catheter shaped electrocatalytic glucose sensor for in vivo application has been developed to determine the glucose level in blood and control the insulin dosage in a closed loop system for diabetes therapy. The principle of measurement is based on the electrochemical oxidation of glucose at a membrane-covered platium electrode. For various potential steps, the impedance obtained at two different frequencies is a function of the glucose concentration. A series of implantations in the vena cava of sheep demonstrated the potential feasibility of the sensor. It was possible to determine the glucose concentration in sheep for more than 130 days with tolerable deviations from glucose reference measurements. The mean error was 2.5 mmol/l. The catheter was explanted after 211 days and histological examination revealed a good biocompatibility of all materials used.

Animals↗

PubMed1993

In vivo experiment with the electrocatalytic glucose sensor in sheep.

In order to control the insulin dosage in diabetes therapy, an electrocatalytic glucose sensor for long-term implantation has been developed. To test the sensor function over a longer period, it was implanted as a flow-through cell in a sheep. The sensor was inserted into the carotid artery and driven by a portable electronic unit worn by the animal. The blood flow characteristics were nearly constant over the whole period of measurement. We were able to verify the sensor performance in one experiment lasting over 71 days. Stable calibrations of the sensor were achieved over longer periods of time, so that only a few calibrations are necessary in monitoring the blood glucose level during the whole period of implantation. It was thus possible to set up a calibration which was valid over 33 days (mean error 2.5 mM). These calibrations were not adversely affected by host reactions. The cross-sensitivity of the sensor was also verified, and it was found that the tested molecules did not significantly affect the sensor function. Only high concentrations of lactate and ethanol require a special adaptation of the calibration to suppress their influence. The sensor will be further improved to obtain a still longer calibration stability, and adapted for animal implantation, thus making it useful for clinical application.

Animals↗

PubMed1991

Influence of urea on the glucose measurement by electrocatalytic sensor in the extracorporeal blood circulation of a sheep.

In an animal experiment with the electrocatalytic glucose sensor, measurements were carried out over one week in the extracorporeal circulation of a sheep. Glucose tolerance tests were performed, and the influence of increased urea concentrations in the blood on the glucose determination was investigated. The sensor constructed as a flow-through cell was integrated via a vascular graft outside the body into the carotid artery of the animal and activated by an external electronic unit of measurement. The glucose concentration was determined by measuring the impedance of the electrode/membrane system at various potentials. By means of a subsequent correlation analysis of the measured values obtained over one week, a calibration valid for the entire measurement period was established. After a zero adjustment, it was even possible to adopt the calibration from the glucose measurement of the preceding animal experiment. The investigations of the influence of urea on the glucose measurement showed that the error in measurement of the sensor, which is 20% on average, is only insignificantly increased when the urea level is raised beyond the maximum physiological concentration.

Animals↗

PubMedDate not supplied

An electrocatalytic glucose sensor for in-vivo application.

An electrocatalytic sensor was developed for continuous measurement of glucose in circulating blood. The sensor is constructed as a flow-through cell that can be integrated into a blood vessel. The principle of measurement is based on the electrochemical oxidation of glucose at an active noble metal electrode. Selectivity is achieved by covering the sensing electrode with a diffusion-limiting membrane and by analyzing the impedance of the electrode/membrane system. The real and the imaginary parts of the impedance at certain potentials are directly proportional to the glucose concentration in the blood. These parameters are used in calculating the blood glucose concentration. To test the sensor, an in-vivo experiment was conducted in a sheep. The sensor's performance remained reliable 71 days after its implantation.

Animals↗