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Biomedical subjects

K Lemke

Publications and source records attributed to K Lemke.

At least 37 records · Page 2Linked to original sources
PubMed1985

In vivo comparison of different algorithms for the artificial beta-cell.

Using an extracorporeal artificial beta-cell in chronically diabetic dogs, the effects of four different mathematical models of glucose-controlled insulin dosage were compared: the Biostator algorithm (quadratic equation), Toronto algorithm (hyperbolic tangent function), Karlsburg algorithm (modified first-order derivative controller), and Ilmenau algorithm (second-order linear difference equation). The constants of all formulas implemented for the artificial beta-cell were obtained by regression analysis of paired blood glucose and plasma insulin data from normal control animals. Thus, they were biologically equivalent for all formulas. The patterns of blood glucose, insulin doses, and plasma insulin before, during, and after an intravenous glucose infusion test performed during the glucose-controlled insulin infusion showed no significant differences between the experimental groups subjected to the different algorithms. However, in no case were really normal blood glucose response curves restored by the artificial beta-cell. This might be due, first, to the fact that the algorithm parameters were not adapted to the actual individual insulin responsiveness, second, to the unphysiological peripheral venous route of insulin administration, and, third, to the lack of appropriate adaptation of the animals to normoglycemia.

Animals↗
PubMed1985

Development of catalytic platinum-binder electrodes for glucose determination.

Compact catalytic platinum-binder glucose sensors were developed, provided for the artificial beta-cell. These consist of three electrodes: the working electrode, a 0.5 mm diameter glass-sheathed platinum wire, covered with a mixture of platinum black and binder (PMMA, PVC) at the face, the reference electrode and the rejuvenating or counter electrode. Measurements were carried out either by a non-equilibrium method within the anodic range or by determination of the current at the anodically directed peak during the cathodic scan. In the first case a periodical switching between rejuvenating and measuring potential takes place and, in the second case, the whole voltammogram is cycled between +1.2 V and -1.2 V (vs. Ag/AgCl). For measurements in phosphate-buffered saline at 37 degrees C the calibration curves exhibit an approximately linear dependence up to a glucose concentration of 30 mM; the sensitivity amounts to 0.3 microA mM-1 and the response times t90% are between 6 and 10 min. A urea concentration of 2.5 mM causes a decrease of the non-equilibrium current of 11.5%-3.0%, and a mixture of amino acids causes a current rise of 11.4%-2.7% with increasing glucose concentration. During the cathodic scan the amino acids affect the peak current negligibly, and the influence of urea reaches saturation for concentrations higher than 6.7 mM. Preliminary in vivo measurements permit the conclusions that after appropriate pretreatment the catalytic glucose sensors can be used for short-time blood glucose monitoring.

Animals↗
PubMed1983

Not the artificial beta cell algorithms but their parameter values are important in automated glucose control of insulin-dependent diabetes.

The blood glucose responses of diabetic dogs on the ABC are nearly identical if different algorithms, but equivalent sets of parameters are used to control the glucose-dependent insulin infusion. There are however some differences in the insulin doses applied, which obviously result from different response kinetics of the particular formula to the minor BG oscillations that always occur. In the practical application of closed-loop systems the control constants should be individually estimated on the basis of certain controlled plant characteristics. For use in patients the checking and modeling systems still have to be simplified. The limits of the study, i.e. the fact that normoglycemia was restored for a short time only using the IV instead of the physiological portal route, remain the subject of further investigation.

Animals↗