Carsten Meyerhoff

Subcutaneous Glucose Concentration in Humans: Real estimation and continuous monitoring

OBJECTIVE To determine the real subcutaneous glucose concentration in healthy volunteers to help in the development of new calibration methods for subcutaneous glucosensors. RESEARCH DESIGN AND METHODS We developed a new method to estimate the real subcutaneous glucose concentration based on the recirculation of phosphate-buffered saline (PBS) in a microdialysis probe inserted into the subcutaneous tissue. Tissue glucose diffuses into the probe until complete equilibration between the glucose concentration outside and inside the microdialysis probe is achieved. Later, the glucose content of the recirculated PBS is assessed in vitro. We applied the method in 10 healthy volunteers under fasting state and during a hyperglycemic clamp. In addition, we monitored the subcutaneous glucose with an enzymatic-amperometric glucosensor combined with a microdialysis probe. RESULTS The subcutaneous glucose concentration measured by the recirculation method was 72 ± 6 and 78 ± 6% of the blood glucose measured in the fasting state and during the hyperglycemic clamps, respectively. On the other hand, the glucosensors signal correlated significantly with the blood glucose. CONCLUSION The recirculation method estimated the real subcutaneous glucose concentration, opening the way to develop new calibration procedures for subcutaneous glucosensors. However, a suitable calibration procedure is still lacking.

Hypoglycaemia Detection by Ulm Sugar Watch System Indicating On-Line s.c. Glucose in Type-1 Diabetic Patients under Intensive Insulin Therapy

This chapter discusses a study focusing on hypoglycaemia detection by Ulm Sugar watch system indicating on-line s.c. glucose in type-1 diabetic patients under intensive insulin therapy. The Ulm Sugar Watch System consists of: (1) microdialysis probe inserted in the s.c. tissue, (2) Glucosensor Unitec Ulm, (3) sensor signal telemetrically transmitted to a wrist watch, (4) optic and acoustic alarm indicating provoked or spontaneous hypoglycaemia, and (5) minutely storage of s.c. glucose concentration for later evaluation before PC. The tissue glucose (T.G.) of patients under intensive-insulin treatment was on-line continuously monitored with glucosensor during hypoglycaemic clamps and under daily therapy. The blood glucose was clamped at 52 ± 4 mg/dl by means of the Bilostator. After clamping, blood glucose was conventionally assessed every 60 or 120 min. Calibration of the glucosensor was achieved by applying a one-point in-vitro , one-point in-vivo method. A further two-point in-vivo calibration and a simple mathematical algorithm a posteriori , yield the smoothing of the sensors signal. The results showed that the blood glucose levels fluctuated between 40 and 400 mg/dl. The sensor signal correlated significantly with the correspondent blood glucose profiles. A delay of 5 to 10 min was determined.