ABSTRACT
BACKGROUND: A novel microdialysis-based continuous glucose monitoring system, the so-called Clinical Research Tool (CRT), is presented. The CRT was designed exclusively for investigational use to offer high analytical accuracy and reliability. The CRT was built to avoid signal artifacts due to catheter clogging, flow obstruction by air bubbles, and flow variation caused by inconstant pumping. For differentiation between physiological events and system artifacts, the sensor current, counter electrode and polarization voltage, battery voltage, sensor temperature, and flow rate are recorded at a rate of 1 Hz. METHOD: In vitro characterization with buffered glucose solutions (c(glucose) = 0 - 26 x 10(-3) mol liter(-1)) over 120 h yielded a mean absolute relative error (MARE) of 2.9 +/- 0.9% and a recorded mean flow rate of 330 +/- 48 nl/min with periodic flow rate variation amounting to 24 +/- 7%. The first 120 h in vivo testing was conducted with five type 1 diabetes subjects wearing two systems each. A mean flow rate of 350 +/- 59 nl/min and a periodic variation of 22 +/- 6% were recorded. RESULTS: Utilizing 3 blood glucose measurements per day and a physical lag time of 1980 s, retrospective calibration of the 10 in vivo experiments yielded a MARE value of 12.4 +/- 5.7. Clarke error grid analysis resulted in 81.0%, 16.6%, 0.8%, 1.6%, and 0% in regions A, B, C, D, and E, respectively. CONCLUSION: The CRT demonstrates exceptional reliability of system operation and very good measurement performance. The ability to differentiate between artifacts and physiological effects suggests the use of the CRT as a reference tool in clinical investigations.
Subject(s)
Blood Glucose Self-Monitoring/instrumentation , Blood Glucose Self-Monitoring/standards , Extracellular Fluid/chemistry , Glucose/analysis , Microdialysis/instrumentation , Microdialysis/standards , Adult , Artifacts , Biosensing Techniques , Blood Glucose/analysis , Blood Glucose Self-Monitoring/methods , Female , Humans , Microdialysis/methods , Middle Aged , Reference Standards , Reproducibility of Results , Time FactorsABSTRACT
Considerable progress in improved control of disturbed glucose metabolism can be expected by continuous glucose monitoring. The aim of the study was to evaluate in male Sprague-Dawley rats tissue response to implantation of a new amperometric glucose-oxidase-based glucose sensor (NTS) compared to a commercially available sensor system CGMS of MiniMed. Both sensors were tested under working conditions over a period of 3 days. Using NTS, glucose in interstitial fluid reflected glucose in arterial blood even in rapidly changing hyper- and hypoglycaemia whereas the CGMS did not detect the experimentally induced glucose changes adequately. Gene expression profiling was performed using Affymetrix chips. Acute phase response to injury by sensor application for a short time is indicated by down regulation of the increase in mRNA of proteases e.g. metallothionein-1alpha and matrix metalloprotease-3 at day 3. Improvement of anabolic situation is suggested by decrease in mRNA of insulin-like growth factor binding protein whereas increase of heme oxygenase and hypoxia-inducible factor may be related to defense mechanisms. Changes of mRNA together with slight fibrous capsule formation suggest good histocompatibility. Comparability of the patterns of changed mRNA in tissue surrounding SCGM with and without operating voltage as shown in dendrogram indicates no contribution of hydrogen peroxide to worsening biocompatibility. Beside established histological investigations of foreign body reaction weeks or months after implantation, gene expression profiling provides additional information to biocompatibility already early after implantation.
Subject(s)
Biosensing Techniques/instrumentation , Blood Glucose Self-Monitoring/adverse effects , Blood Glucose Self-Monitoring/instrumentation , Blood Glucose/analysis , Foreign-Body Reaction/diagnosis , Foreign-Body Reaction/etiology , Glucose Oxidase/chemistry , Animals , Equipment Design , Equipment Failure Analysis , Male , Rats , Rats, Sprague-Dawley , Reproducibility of Results , Sensitivity and SpecificityABSTRACT
BACKGROUND: This study investigated continuous glucose profiles in nondiabetic subjects. METHODS: Continuous interstitial glucose measurement was performed under everyday life conditions (2 days) and after ingestion of four meals with standardized carbohydrate content (50 grams), but with different types of carbohydrates and variable protein and fat content. Twenty-four healthy volunteers (12 female, 12 male, age 27.1 +/- 3.6 years) participated in the study. Each subject wore two microdialysis devices (SCGM1, Roche Diagnostics) simultaneously. RESULTS: The mean 24-hour interstitial glucose concentration under everyday life conditions was 89.3 +/- 6.2 mg/dl (mean +/- SD, n = 21), and mean interstitial glucose concentrations at daytime and during the night were 93.0 +/- 7.0 and 81.8 +/- 6.3 mg/dl, respectively. The highest postprandial glucose concentrations were observed after breakfast: 132.3 +/- 16.7 mg/dl (range 101-168 mg/dl); peak concentrations after lunch and dinner were 118.2 +/- 13.4 and 123.0 +/- 16.9 mg/dl, respectively. Mean time to peak glucose concentration was between 46 and 50 minutes. After ingestion of standardized meals with fast absorption characteristics, peak interstitial glucose concentrations were 133.2 +/- 14.4 and 137.2 +/- 21.1 mg/dl, respectively. Meals with a higher fiber, protein, and fat content induced a smaller increase and a slower decrease of postprandial glucose concentrations with peak values of 99.2 +/- 10.5 and 122.1 +/- 20.4 mg/dl, respectively. CONCLUSIONS: This study provided continuous glucose profiles in nondiabetic subjects and demonstrated that differences in meal composition are reflected in postprandial interstitial glucose concentrations. Regarding the increasing application of continuous glucose monitoring in diabetic patients, these data suggest that detailed information about the ingested meals is important for adequate interpretation of postprandial glucose profiles.
