OBJECTIVE—The most promising β-cell replacement therapy for children with type 1 diabetes is a closed-loop artificial pancreas incorporating continuous glucose sensors and insulin pumps. The Medtronic MiniMed external physiological insulin delivery (ePID) system combines an external pump and sensor with a variable insulin infusion rate algorithm designed to emulate the physiological characteristics of the β-cell. However, delays in insulin absorption associated with the subcutaneous route of delivery inevitably lead to large postprandial glucose excursions.

RESEARCH DESIGN AND METHODS—We studied the feasibility of the Medtronic ePID system in youth with type 1 diabetes and hypothesized that small manual premeal “priming” boluses would reduce postprandial excursions during closed-loop control. Seventeen adolescents (aged 15.9 ± 1.6 years; A1C 7.1 ± 0.8%) underwent 34 h of closed-loop control; 8 with full closed-loop (FCL) control and 9 with hybrid closed-loop (HCL) control (premeal priming bolus).

RESULTS—Mean glucose levels were 135 ± 45 mg/dl in the HCL group versus 141 ± 55 mg/dl in the FCL group (P = 0.09); daytime glucose levels averaged 149 ± 47 mg/dl in the HCL group versus 159 ± 59 mg/dl in the FCL group (P = 0.03). Peak postprandial glucose levels averaged 194 ± 47 mg/dl in the HCL group versus 226 ± 51 mg/dl in the FCL group (P = 0.04). Nighttime control was similar in both groups (111 ± 27 vs. 112 ± 28 mg/dl).

CONCLUSIONS—Closed-loop glucose control using an external sensor and insulin pump provides a means to achieve near-normal glucose concentrations in youth with type 1 diabetes during the overnight period. The addition of small manual priming bolus doses of insulin, given 15 min before meals, improves postprandial glycemic excursions.