Pilot Study of Closed-Loop Glucose Control in People With Type 1 Diabetes (BPK004)

Overview

This study plans to link two existing technologies, the insulin pump and the continuous glucose monitor (CGM), to essentially develop an artificial pancreas, i.e., closed-loop. This will be done using two continuous glucose monitors (CGMs), a computer containing an investigational control algorithm that uses glucose information from the CGM to recommend insulin dosing, and an insulin pump. The purpose of this study is to test the ability of continuous glucose monitors together with an insulin pump and a mathematical formula to control blood sugar levels of people with type 1 diabetes. The Closed-Loop control algorithm will: 1. Suggest adequate insulin delivery for blood glucose control in steady state (overnight); 2. Cover adequately with an insulin bolus the pre-set carbohydrate content of a breakfast. If successful, this study will conceptually prove the feasibility of automated model-predictive closed-loop glucose control in T1DM.

Each patient had an outpatient screening evaluation, and two 22 h overnight hospital admissions separated by a 2- to 4-week waiting period. Each inpatient admission began at 15:00 and ended at 13:00 on the following day. Subjects ate dinners and lunches with carbohydrate content that was the same at admission 1 and admission 2 and had identical morning meals of Ensure Plus (Abbott Nutrition, Columbus, OH). Two days before each admission, two Freestyle Navigator CGM devices (Abbott Diabetes Care) continuous glucose monitors were applied to the patient to allow for stabilization of the sensors and for assessment of their performance. During admission 1, open-loop control was used, with the subjects' usual insulin routine and their personal insulin pump. During admission 2, an OmniPod Insulin Management System (Insulet Corp.) was inserted and used for closed-loop control of blood glucose. Insulin lispro (Eli Lilly, Indianapolis, IN), chosen based on commercial assays available, was used during both inpatient admissions. At the beginning of admission 2, one of the two CGM devices was designated as primary, and the closed-loop control algorithm used the data of that system, unless a problem was detected. At 17:00, the model-predictive control (MPC) was initiated in a data-collection mode, automatically receiving CGM data every minute. Administration of the predinner insulin bolus was overseen by the attending physician. MPC, closed-loop control began at 21:30 and continued until 12:00 the next day for a total of 14.5 h. Per FDA restrictions, the algorithm did not automatically control the insulin pump. Instead, the algorithm suggested insulin boluses every 15 min, which, if accepted, were programmed into the insulin pump by the attending physician. This was done for safety reasons, allowing the physician to override insulin delivery suggestions at any time. Reference blood glucose (using a YSI Life Sciences or a Beckman glucose analyzer) was sampled every 30 min. The protocol required switching to more frequent 15 min reference blood glucose sampling if hypoglycemia occurred or was imminent. Fast-acting carbohydrate (glucose tablets or fruit juice) was given when reference blood glucose fell below 3.9 mmol/liter, regardless of the CGM readings.