Background: Automated insulin delivery, or closed-loop (CL), systems are emerging as a management tool for individuals with T1D. The MiniMed™ 670G system is a single hormone hybrid closed-loop (HCL) system that adjusts basal insulin delivery based on sensor glucose (SG)levels and is already used in clinical practice. An enhanced HCL system (e-HCL) prototype with an automated correction bolus feature was developed and evaluated in a small feasibility study.

Methods: Subjects (n=12) aged a mean±SD of 17.6±2.9 years with T1D and an A1C of 7.3±0.7% (56.5±7.7 mmol/mol) completed a 6-day run-in period with the e-HCL system in open-loop (OL) (i.e., Auto Mode OFF and Suspend before low ON). Thereafter, a supervised hotel period (6 days/5 nights) with CL challenges (missed meal bolus, late meal bolus, and physical activity) was completed, and followed by a 3-week at-home period with Auto Mode and automated correction boluses ON, without restrictions. Glycemic control was compared between the OL run-in period and CL period.

Results: During the at-home period, subjects spent 93±4% of the time in Auto Mode. Time within target glucose range of 70-180 mg/dL (3.9-10.0 mmol/L) increased from 68.8±10.5% to 74±6.1%, time >180 mg/dL reduced from 27.1±11.9% to 23.7±8.8%, and time <70mg/dL dropped from 4.1±3.7% to 3±2.8%. Total daily insulin dose was 56.3±10.9 units and 53.4±12.5 units during the OL run-in and CL periods, respectively. A greater percentage of insulin was delivered as bolus than as basal, during the CL period (54.3±8.9% versus 41.7±4.36%). No serious adverse events occurred.

Conclusions: Incorporating automated correction boluses to an HCL system was safe and effective in controlling day and night glucose levels, during a 3-week at-home period.


R. Nimri: Employee; Self; DreaMed Diabetes. Research Support; Self; Dexcom, Inc., Glooko, Inc., Insulet Corporation, JDRF, Medtronic, National Institutes of Health. Speaker's Bureau; Self; Lilly Diabetes. Stock/Shareholder; Self; DreaMed Diabetes. B. Grosman: Employee; Self; Medtronic. N. Kurtz: Employee; Self; Medtronic MiniMed, Inc. A. Roy: Employee; Self; Medtronic MiniMed, Inc. J. Nir: None. N. Loewenthal: None. F.R. Kaufman: Employee; Self; Medtronic. M. Phillip: Consultant; Self; Qulab Medical, RSP Systems A/S. Research Support; Self; Bristol-Myers Squibb Company, Dexcom, Inc., JDRF, Lexicon Pharmaceuticals, Inc., Merck & Co., Inc., OPKO. Stock/Shareholder; Self; DreaMed Diabetes, Ltd., NG Solutions Ltd., Nutriteen Professional Ltd. Other Relationship; Self; AstraZeneca, Eli Lilly and Company, Insulet Corporation, Medtronic MiniMed, Inc., Novo Nordisk A/S, Pfizer Inc., Sanofi-Aventis.

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