A Run-to-Run Control Strategy to Adjust Basal Insulin Infusion Rates in Type 1 Diabetes

Abstract

Maintaining good glycemic control is a daily challenge for people with type 1 diabetes. Insulin requirements are changing constantly due to many factors, such as levels of stress and physical activity. The basal insulin requirement also has a circadian rhythm, adding another level of complexity. Automating the adjustment of insulin dosing would result in improved glycemic control, as well as an improved quality of life by significantly reducing the burden on the patient. Building on our previous success of using run-to-run control for prandial insulin dosing (a strategy adapted from the chemical process industry), we show how this same framework can be used to adjust basal infusion profiles. We present a mathematical model of insulin-glucose dynamics which we augment in order to capture the circadian variation in insulin requirements. Using this model, we show that the run-to-run framework can also be successfully applied to adjust basal insulin dosing.

Figures

Fig. 1

Two-day sequence (starting at midnight) of CGMS blood glucose data before the adjustment of basal rates; the subject skipped breakfast on the second day. The hyperglycemic excursion during the night indicates that the basal infusion rate for this period is too low, while the morning segment of the second day is correct. Diamonds indicate the capillary blood glucose calibration measurements.

Fig. 2

Two-day sequence (starting at midnight) of CGMS blood glucose data after the adjustment of basal rates; the subject skipped breakfast on first day. Nighttime and morning basal rates are correctly set. Diamonds indicate the capillary blood glucose calibration measurements.

Fig. 3

Nominal basal segments for a day, indicating meal and blood glucose measurement times.

Fig. 4

Blood glucose response over a day with the corresponding basal infusion profile. The circles indicate the timepoints at which blood glucose measurements are taken for use by the algorithm, and the triangles indicating the starting time of meals.

Fig. 5

Blood glucose response over 10 days with the corresponding basal infusion profile for case eight. The dotted line in the insulin plot indicates the optimal basal infusion profile. Initial basal rates are set according to the clinical heuristics, with segment one slightly underdosed, segment two is overdosed, segment three is very close to target, and segment four is underdosed. These settings result in periods of hyper- and hypoglycemia, with levels converging to clinically acceptable levels by the fifth day.

Fig. 6

Blood glucose response for day seven of the simulation run for case eight. The dotted line in the insulin plot indicates the optimal basal infusion profile. The blood glucose profile shows good glycemic control over the day, with the basal infusion rates being very close to the optimal rates.

Fig. 7

Blood glucose response over 15 days for the worst case (number ten). The initial setting based on the clinical heuristics are significantly off, with the subject showing high insulin sensitivity in all but the morning segment, which has significantly higher insulin requirements. The dotted line in the insulin plot indicates the optimal basal infusion profile.