Continuous Glucose Monitoring—A Study of the Enlite Sensor During Hypo- and Hyperbaric Conditions

Göteborg Pediatric Growth Research Center, Department of Pediatrics, Institute of Clinical Sciences, Sahlgrenska Academy at University of Gothenburg, Göteborg, Sweden.
Diabetes Technology & Therapeutics (Impact Factor: 2.11). 03/2012; 14(6):527-32. DOI: 10.1089/dia.2011.0284
Source: PubMed


The performance and accuracy of the Enlite(™) (Medtronic, Inc., Northridge, CA) sensor may be affected by microbubble formation at the electrode surface during hypo- and hyperbaric conditions. The effects of acute pressure changes and of prewetting of sensors were investigated.
On Day 1, 24 sensors were inserted on the right side of the abdomen and back in one healthy individual; 12 were prewetted with saline solution, and 12 were inserted dry. On Day 2, this procedure was repeated on the left side. All sensors were attached to an iPro continuous glucose monitoring (CGM) recorder. Hypobaric and hyperbaric tests were conducted in a pressure chamber, with each test lasting 105 min. Plasma glucose values were obtained at 5-min intervals with a HemoCue(®) (Ängelholm, Sweden) model 201 glucose analyzer for comparison with sensor glucose values.
Ninety percent of the CGM systems operated during the tests. The mean absolute relative difference was lower during hyperbaric than hypobaric conditions (6.7% vs. 14.9%, P<0.001). Sensor sensitivity was slightly decreased (P<0.05) during hypobaric but not during hyperbaric conditions. Clarke Error Grid Analysis showed that 100% of the values were found in the A+B region. No differences were found between prewetted and dry sensors.
The Enlite sensor performed adequately during acute pressure changes and was more accurate during hyperbaric than hypobaric conditions. Prewetting the sensors did not improve accuracy. Further studies on type 1 diabetes subjects are needed under various pressure conditions.

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    ABSTRACT: BACKGROUND: The accuracy and efficacy of the Medtronic Diabetes (Northridge, CA) Real-Time (RT)-Continuous Glucose Monitoring (CGM) sensor were analyzed in 72 subjects with type 1 diabetes. METHODS: This was a retrospective analysis of 60,050 temporally paired data points (sensor and glucose meter values) obtained during the course of an outpatient ambulatory study evaluating the efficacy of a sensor-augmented pump system in adults and adolescents. Subjects uploaded sensor values and self-monitoring blood glucose data to the CareLink Clinical Application (Medtronic Diabetes) via the Internet, every 2 weeks during the course of the study. RESULTS: The overall percentage of sensor readings within +/-20% or +/-30% agreement of reference glucose readings was 75.6% and 86.8%, respectively. The highest rate of agreement occurred in the 240-400 mg/dL range, where 79.9% of sensor readings were within +/-20% of meter values and 91.5% of sensor readings were within 30% of meter values. The mean absolute relative difference for all subjects was 15.8%, and the median absolute relative difference was 10.9%. The bias was -2.13 mg/dL. Paired glucose measurements from the RT-CGM and meter demonstrated that 95.9% of paired points in the overall subject population fell in zones A and B of the Clarke Error Grid. Consensus Error Grid Analysis established that 99.2% of paired data points were in zones A and B. CONCLUSIONS: This study reports the accuracy of a continuous glucose sensor with a large number of paired data points (60,050). RT-CGM is safe and well tolerated and provides readings that are in close agreement with glucose meter values.
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  • No preview · Article · Oct 2012 · Diabetes Technology & Therapeutics
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    ABSTRACT: Background: There is a need for reliable methods of glucose measurement in different environmental conditions. The objective of this in vitro study was to evaluate the performance of the Enlite® Sensor when connected to either the iPro™ Continuous Glucose Monitor recording device or the Guardian® REAL-Time transmitting device, in hypobaric and hyperbaric conditions. Methods: Sixteen sensors connected to eight iPro devices and eight Guardian REAL-Time devices were immersed in three beakers containing separate glucose concentrations: 52, 88, and 207 mg/dl (2.9, 4.9, and 11.3 mmol/liter). Two different pressure tests were conducted: a hypobaric test, corresponding to maximum 18000 ft/5500 m height, and a hyperbaric test, corresponding to maximum 100 ft/30 m depth. The linearity of the sensor signals in the different conditions was evaluated. Results: The sensors worked continuously, and the sensor signals were collected without interruption at all pressures tested. When comparing the input signals for glucose (ISIGs) and the different glucose concentrations during altered pressure, linearity (R(2)) of 0.98 was found. During the hypobaric test, significant differences (p < .005) were seen when comparing the ISIGs during varying pressure at two of the glucose concentrations (52 and 207 mg/dl), whereas no difference was seen at the 88 mg/dl glucose concentration. During the hyperbaric test, no differences were found. Conclusions: The Enlite Sensors connected to either the iPro or the Guardian REAL-Time device provided values continuously. In hyperbaric conditions, no significant differences were seen during changes in ambient pressure; however, during hypobaric conditions, the ISIG was significantly different in the low and high glucose concentrations.
    Full-text · Article · Nov 2012 · Journal of diabetes science and technology
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