Evaluating the Performance of a Novel Embedded Closed-loop System

Abstract

The objective was to assess the reliability of a novel automated closed-loop glucose control system developed within the AP@home consortium in adults with type 1 diabetes. Eight adults with type 1 diabetes on insulin pump therapy (3 men; ages 40.5 ± 14.3 years; HbA1c 8.2 ± 0.8%) participated in an open-label, single-center, single-arm, 12-hour overnight study performed at the clinical research facility. A standardized evening meal (80 g CHO) accompanied by prandial insulin boluses were given at 19:00 followed by an optional snack of 15 g at 22:00 without insulin bolus. Automated closed-loop glucose control was started at 19:00 and continued until 07:00 the next day. Basal insulin delivery (Accu-Chek Spirit, Roche) was automatically adjusted by Cambridge model predictive control algorithm, running on a purpose-built embedded device, based on real-time continuous glucose monitor readings (Dexcom G4 Platinum). Closed-loop system was operational as intended over 99% of the time. Overnight plasma glucose levels (22:00 to 07:00) were within the target range (3.9 to 8.0 mmol/l) for 75.4% (37.5, 92.9) of the time without any time spent in hypoglycemia (<3.9 mmol/l). Mean overnight glucose was 7.8 ± 1.3 mmol/l. For the entire 12-hour closed-loop period (19:00 until 07:00) plasma glucose levels were within the target range (3.9 to 10.0 mmol/l) for 84.4% (63.3, 100) of time. There were no adverse events noted during the trial. We observed a high degree of reliability of the automated closed-loop system. The time spent in target glucose level overnight was comparable to results of previously published studies. Further developments to miniaturize the system for home studies are warranted.

Keywords: AP@home consortium; Dexcom G4 Platinum; MPC algorithm; closed-loop; continuous glucose monitoring.

Figure 1.

Design of the closed-loop system. On the right side of the figure separated by the dashed line are the components attached to the patient (Spirit Combo insulin pump and Dexcom G4 transmitter). artificial pancreas platform (APP) unit contains a dedicated main processor running the algorithm and a safety processor. APP unit and the Dexcom receiver are attached to a laptop computer that has the user interface.

Figure 2.

Plasma glucose, insulin infusion, and plasma insulin levels. Data shown are median (IQR).

Figure 3.

The Clarke error grid of sensor and reference glucose levels.