OPEN-FLOW MICROPERFUSION OF SUBCUTANEOUS ADIPOSE-TISSUE FOR ONLINE CONTINUOUS EX-VIVO MEASUREMENT OF GLUCOSE-CONCENTRATION

OBJECTIVE - To evaluate a novel technique for on-line continuous gluco se measurement in subcutaneous adipose tissue, and to investigate its accuracy for detection of hypoglycemia. RESEARCH DESIGN AND METHODS - The method combined an open-flow microperfusion of subcutaneous adipos e tissue using a double lumen catheter and an extracorporeal sensor ce ll. An isotonic ion-free solution was perfused through the inner lumen of the catheter. equilibrated with the subcutaneous tissue fluid, and sampled through the outer lumen. The recovery was continuously monito red as the ratio between the measured sampled fluid conductivity and t he subcutaneous tissue fluid conductivity (assumed to have a constant value of 1.28 S/m at 25 degrees C). Glucose concentration was calculat ed on-line from the measured glucose in the sampled fluid and the meas ured recovery in healthy volunteers during hyperglycemic glucose loads (n = 8), hypoglycemic hyperinsulinemic clamp (n = 6), and a 24-h moni toring period (n = 7). RESULTS - Subcutaneous glucose concentrations i n the fasting state were 94% of the plasma glucose concentrations in a rterialized venous samples. According to the error grid analysis, 96.9 % of the on-line measured subcutaneous glucose concentrations during h yperglycemia and 96.3% during hypoglycemia were in accurate or accepta ble zones. The mean differences between the measured subcutaneous gluc ose and the actual plasma glucose concentration were -0.06-3.3 mmol/l (hyperglycemia). and -0.6-1.1 mmol/l (hypoglycemia). CONCLUSIONS - By combining open-flow microperfusion, glucose sensor, and conductivity m easurement. glucose concentration in the subcutaneous adipose tissue c an be monitored on-line. extracorporeally and continuously without any in vivo calibration, and gives accurate measurements during hyper- an d hypoglycemia.