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- Title
Time Lag of a Seven-Day Transcutaneous Glucose Sensor Compared to YSI Blood Glucose Values.
- Authors
Brauker, James; Kamath, Apurv; Li, Ying; Zisser, Howard; Schwartz, Sherwyn; Ratner, Robert; Wise, Jonathan; Bailey, Timothy
- Abstract
Alternate site studies of the fingertip vs. forearm have identified time lags of up to 38 minutes, which is thought to be due to a greater Contribution from interstitial fluid ISF in the forearm. This time-lag can be overcome by perturbing the fluid distribution in the forearm using modulated pressure application (Stout et al, Diabet Tech Ther 2004 6:635). Because needle inserted transcutaneous glucose sensors are thought to mainly measure ISF, we examined the magnitude of the time-lag between sensor values obtained with the DexCom™ STS™ 7 sensor and samples obtained from venous blood measured by a Yellow Springs Instrument (YSI). Seventy-two insulin dependent diabetes subjects at 5 sites were enrolled in a non-randomized study. Subjects inserted and wore 1 or 2 Sensors for 7 days. Sensors were inserted in abdominal subcutaneous tissue. All subjects participated in one 10-hour in-clinic session on Day 1, 4, or 7 in which YSI samples were determined every 20 minutes. Time-lag analysis was performed on 88 sensors that had at least 8 hours of corresponding YSI data. Time-lag was determined by finding the optimal correlation coefficient (R) between raw sensor data and YSI data when the sensor data were shifted in 5 -minute increments. Mean R ± Standard Deviation was 0.95 ± 0.10. Mean time-lag (minutes) was 5.18 ± 4.85, and median time-lag was 5.0. Ninety-two percent (92%) of sensors had a time-lag of 10 minutes or less, and no time-lag exceeded 15 minutes. These data show that most sensors have negligible ISF time-lags when sensors are implanted in the abdominal region. It is likely that, like the forearm, the ISF in the abdominal region is in slow equilibrium with blood, resulting in a lag in blood glucose concentration under native conditions. We hypothesize that the perturbation of the subcutaneous tissue by the sensor insertion, with continued stimulation by the presence of the sensor in the tissue, promotes more rapid equilibrium between blood and ISF than is normally seen in native ISF.
- Subjects
BLOOD sugar monitoring; BLOOD sugar analysis; BIOSENSORS; DIABETES; PEOPLE with diabetes
- Publication
Diabetes, 2007, Vol 56, pA119
- ISSN
0012-1797
- Publication type
Article