Performance of Medtronic Hybrid Closed-Loop Iterations, Results from a Randomized Trial in Adolescents with Type 1 Diabetes

This study investigates the performance of an iteration of the Medtronic hybrid closed-loop (HCL) algorithm, which utilizes sensor glucose values non-adjunctively for bolus advice, recognizes sustained hyperglycemia, suggests insulin bolus correction, and includes more accommodative SmartGuard automode parameters that aim to improve function and usability. Adolescents aged 13-17 years with type 1 diabetes >1 year, glycated hemoglobin (HbA(1c)) 7.0%-10%, currently using Continuous Subcutaneous Insulin Infusion were randomized to the control Medtronic standard HCL algorithm or to the intervention Medtronic HCL with enhancements. Participants attended a 7-day and 7-night nonstructured camp setting. Twelve participants (mean age 15 years, seven males, five females, mean HbA(1c) 8.55%) completed the study. For the control group, time in target glucose sensor range (3.9-10mmol/L) was 63.68%+/- 10.74% at baseline and changed to 75.85%+/- 8.49% during the study (relative 19%). Time spent in <2.8mmol/L was 0.61%+/- 0.79% at baseline for the control group and changed to 0.32%+/- 0.31% during the study for the control group (relative 48%). In the intervention group, time in target glucose sensor range (3.9-10mmol/L) was 52.15%+/- 9.55% at baseline and changed to 74.32%+/- 8.41% during the study (relative 42%). Time spent in <2.8mmol/L was 1.07%+/- 1.77% at baseline for the intervention group and changed to 0.24%+/- 0.14% during the study for the intervention group (relative 78%). Mean sensor glucose was 8.05 +/- 0.73mmol/L and 8.22 +/- 0.56mmol/L for the control and intervention participants. SmartGuard automode exit frequency was 0.54 exits per person per day for control and 0.12 exits per person per day for the intervention. Participants were in active SmartGuard automode 97.1% and 98.8% of the time for the control and intervention, respectively. Alarm frequency was 2.1 alarms per person per day for the control arm, and 0.26 alarms per person per day in the intervention arm. Feasibility of the enhanced HCL algorithm was demonstrated with a high proportion of time spent in SmartGuard automode and target glucose range. The iterative changes resulted in less SmartGuard automode exits without compromising glycemic control.