COMBINATION OF MICRODIALYSIS AND GLUCOSE SENSOR FOR CONTINUOUS ON LINE MEASUREMENT OF THE SUBCUTANEOUS GLUCOSE-CONCENTRATION - THEORY AND PRACTICAL APPLICATION

The microdialysis technique can be used to get dialysates of the subcu taneous tissue, which can be continuously measured by an amperometric glucose sensor. In order to get further insight into the microdialysis procedure, we used a steady-state theory for microdialysis to predict the recovery of glucose in the dialysate and compared the results to experimental data obtained by a combination of the microdialysis techn ique with continuous amperometric glucose sensing. The recovery of glu cose obtained in vitro for two different microdialysis probes was clos e to the theoretical predictions. When quantifying the predictions of the model with regard to the spatial concentration profile in the subc utaneous tissue, it appeared, that the presence of the microdialysis p robe depressed the concentration of glucose for 0.2 mm from the probe surface. In a 24 hour in vivo experiment, there were less fluctuations in the sensor signal when the patient was lying in bed compared to th e time, when the patient could move freely. In conclusion, the combina tion of microdialysis and glucose sensor seems to be a promising appro ach to a continuously functioning glucose sensing system. However, the microdialysis procedure itself disturbs the surrounding of the probe leading to a concentration gradient of glucose. This might explain som e differences between the course of blood glucose and the course of su bcutaneous glucose, measured by the combination of microdialysis and a n amperometric glucose sensor. Further developments of such systems sh ould aim at implanting microdialysis devices which have a minimal infl uence upon the tissue metabolism.