Monitoring of Biofluids in Microsamples Investigations for Glucose Monitoring using Open-Flow Microperfusion

Open-flow microperfusion enables the direct access to the interstitial fluid (ISF). This method is based on a double lumen catheter with macroscopic perforations. The catheter is inserted into the subcutaneous adipose tissue and constantly perfused. Thus partial equilibration (recovery) between the ISF and the perfusion fluid occurs. After modeling the exchange process, different calibration procedures were developed: the "zero flow rate"- and "no net flux" protocols, the "recirculation"-, "endogenous"- and the "ionic reference" techniques. These different calibration procedures were used to determine the glucose concentration of the ISF and were compared with each other. In addition, the electrical conductivity of the ISF as a measure of the overall ion concentrations was determined combining the no net flux protocol, the recirculation technique and conductivity sensors. The glucose concentration in the ISF was determined during hypo-, eu- and hyperglycemia. Long term glucose monitoring was performed in lean as well as normal weighted volunteers in order to determine the influence of the skinfold thickness on the recovery. Finally, the glucose concentration in the ISF was measured continuously combining open-flow microperfusion and sensor techniques.