Reduced Hypoglycemia and Increased Time in Target Using Closed-Loop Insulin Delivery During Nights With or Without Antecedent Afternoon Exercise in Type 1 Diabetes

  1. Stuart A. Weinzimer, MD1
  1. 1Department of Pediatrics, Yale University School of Medicine, New Haven, Connecticut
  2. 2Medtronic Diabetes, Northridge, California
  1. Corresponding author: Jennifer L. Sherr, jennifer.sherr{at}


OBJECTIVE Afternoon exercise increases the risk of nocturnal hypoglycemia (NH) in subjects with type 1 diabetes. We hypothesized that automated feedback-controlled closed-loop (CL) insulin delivery would be superior to open-loop (OL) control in preventing NH and maintaining a higher proportion of blood glucose levels within the target blood glucose range on nights with and without antecedent afternoon exercise.

RESEARCH DESIGN AND METHODS Subjects completed two 48-h inpatient study periods in random order: usual OL control and CL control using a proportional-integrative-derivative plus insulin feedback algorithm. Each admission included a sedentary day and an exercise day, with a standardized protocol of 60 min of brisk treadmill walking to 65–70% maximum heart rate at 3:00 p.m.

RESULTS Among 12 subjects (age 12–26 years, A1C 7.4 ± 0.6%), antecedent exercise increased the frequency of NH (reference blood glucose <60 mg/dL) during OL control from six to eight events. In contrast, there was only one NH event each on nights with and without antecedent exercise during CL control (P = 0.04 vs. OL nights). Overnight, the percentage of glucose values in target range was increased with CL control (P < 0.0001). Insulin delivery was lower between 10:00 p.m. and 2:00 a.m. on nights after exercise on CL versus OL, P = 0.008.

CONCLUSIONS CL insulin delivery provides an effective means to reduce the risk of NH while increasing the percentage of time spent in target range, regardless of activity level in the mid-afternoon. These data suggest that CL control could be of benefit to patients with type 1 diabetes even if it is limited to the overnight period.

  • Received January 2, 2013.
  • Accepted April 6, 2013.

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