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Diabetes Technol Ther. 2017 Jul;19(7):433-437. doi: 10.1089/dia.2016.0307. Epub 2017 May 2.

Behavioral Patterns and Associations with Glucose Control During 12-Week Randomized Free-Living Clinical Trial of Day and Night Hybrid Closed-Loop Insulin Delivery in Adults with Type 1 Diabetes.

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1 Wellcome Trust-MRC Institute of Metabolic Science, University of Cambridge , Cambridge, United Kingdom .
2 Department of Paediatrics, University of Cambridge , Cambridge, United Kingdom .
3 Department of Diabetes & Endocrinology, Cambridge University Hospitals NHS Foundation Trust , Cambridge, United Kingdom .
4 Central Manchester University Hospitals NHS Foundation Trust and University of Manchester , Manchester, United Kingdom .
5 Profil, Neuss, Germany .
6 Division of Endocrinology and Diabetology, Department of Internal Medicine, Medical University of Graz , Graz, Austria .



We evaluated patterns of meal intake, insulin bolus delivery, and fingerstick glucose measurements during hybrid closed-loop and sensor-augmented pump (SAP) therapy, including associations with glucose control.


Data were retrospectively analyzed from pump-treated adults with type 1 diabetes who underwent, in random order, 12 weeks free-living closed-loop (n = 32) and 12 weeks SAP (n = 33) periods. We quantified daily patterns of main meals, snacks, prandial insulin boluses, correction boluses, and fingerstick glucose measurements by analyzing data recorded on the study glucometer and on study insulin pump.


We analyzed 1942 closed-loop days and 2530 SAP days. The total number of insulin boluses was reduced during closed-loop versus SAP periods by mean 1.0 per day (95% confidence interval 0.6-1.4, P < 0.001) mainly because of a reduced number of correction boluses by mean 0.7 per day (0.4-1.0, P < 0.001). Other behavioral patterns were unchanged. The carbohydrate content of snacks but not the number of snacks was positively correlated with (1) glycemic variability as measured by standard deviation of sensor glucose (closed-loop P < 0.05; SAP P < 0.01), (2) mean sensor glucose (P < 0.05), and (3) postintervention HbA1c (P < 0.05). Behavioral patterns explained 47% of between-subject variance in glucose variability during SAP period and 30%-33% of variance of means sensor glucose and postintervention HbA1c.


Fewer correction boluses are delivered during closed-loop period. The size of snacks appears to worsen glucose control possibly because of carbohydrate-rich content of snacks. Modifiable behavioral patterns may be important determinants of glucose control.


Behavior; Closed-loop systems; Insulin boluses; Meals; Type 1 diabetes

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