Preventing Hypoglycemia During Exercise With Proactive Snacking on Closed Loop

This study will be a randomized cross-over study as subjects will be studied under both study conditions - Closed Loop (CL) alone vs. CL + proactive snacking protocol). Differences in the nadir blood glucose levels during exercise between the two study conditions will be the primary outcome measure.

• Medtronic MiniMed Closed Loop (CL) System (Device): The Medtronic MiniMed Closed Loop (CL) System is an investigational system that uses some commercially available products. An investigational Enlite 2 glucose sensor measures the sensor glucose. The glucose sensor signal is sent to the insulin pump. From the insulin pump the sensor glucose is sent through the translator, which then relays the signal on to a controller. An Android Mobile Device (off the shelf) has the control algorithm installed. This device is known as the controller. The controller serves as the control center for the Android system, receiving data from the sensor and pump components, feeding the data to its control algorithm, issuing delivery commands to the pump to apply the algorithm's recommend therapy, and providing a means to monitor the system.
• Snacking (Other), also known as Oral glucose: Up to 45 g of oral glucose via Gatorade

Primary outcomes

• Nadir blood glucose levels during exercise [75 minutes]: Difference in the nadir blood glucose levels during exercise between the two study conditions: Closed Loop alone vs. Closed Loop+ snacking.

Secondary outcomes

• Episodes of hypoglycemia (blood glucose <60mg/dL) during exercise [75 minutes]: Percentage of subjects that required treatment for hypoglycemia during the exercise period between the two study conditions
• Mean reduction in blood glucose during exercise [75 minutes]: Mean Reduction in blood glucose from baseline blood glucose during exercise
• Mean time blood glucose in target during exercise [75 minutes]: Comparison of the mean time blood glucose levels were between 70-180mg/dL during exercise between the two study conditions
• Mean time blood glucose levels are in target during the overnight period [17 hours]: Comparison of the mean time blood glucose levels are in target (70-180mg/dL) during the overnight period after mid-afternoon exercise.
• Mean glucose values [12 hours]: Comparison of the mean daytime and nighttime glucose values
• Mean 24- hour glucose levels [24 hours]: Comparison of the mean 24- hour glucose levels
• insulin delivery during CL therapy [24 hours]: Differences between insulin delivery during CL therapy during the two study conditions (pro-active snacking vs. no snacking) will be assessed.
• Incremental meal-related glucose Area Under the Curve [24 hours]: Assessment of incremental meal related glucose area under the curve will be conducted.
• Nadir glucose levels following the meals [24 hours]: Nadir glucose levels following meals will be compared between the two study conditions
• Area under the curve meal-related plasma insulin level excursion following meals [24 hours]: Area under the curve meal-related insulin excursion following meals.
• Nadir glucose levels overnight [12 hours]: Difference between nadir glucose levels between the two study conditions will be assessed.
• Mean absolute relative difference (MARD) for each sensor [24 hours]: Calculation and comparison of the mean absolute relative difference for each sensor will be performed and comparisons between accuracy of the sensors will be done.
• Mean daytime and nighttime glucose values [24 hours]: Comparison of the mean daytime and nighttime glucose levels

Sex: All, ages: 13 Years to 44 Years

Inclusion Criteria:

1. Age 13-45 years
2. Clinical diagnosis of T1D (formal antibody and/or genetic testing will not be required)
3. Duration of T1D ≥ 1 year
4. HbA1c ≤ 9 %
5. Treated with continuous subcutaneous insulin infusion (pump) for at least 3 months
6. Body weight > 40 kg (to accommodate phlebotomy)
7. Able to tolerate a 75-minute exercise period of moderate intensity
8. Be willing to wear 2 subcutaneous glucose sensors (placed under the skin like a pump site) simultaneously during the inpatient portions of this study.
9. Be in good general health without other acute or chronic illness that in the judgment of the investigator could interfere with the study or jeopardize subject safety
10. Normal hematocrit
11. Able to give consent (for children <18 years, permission from parents and subject assent will be required)
12. Female subjects of reproductive potential must be abstinent or consistently using appropriate family planning methods.

Exclusion Criteria:

1. Insulin resistant (defined as requiring > 1.5 units/kg/day at time of study enrollment)
2. Presence of any medical or psychiatric disorder that may interfere with subject safety or study conduct
3. Use of any medications (besides insulin) known to effect blood glucose levels, including oral or other systemic glucocorticoid therapy. Inhaled, intranasal, or rectal corticosteroid use is allowed along as not given within 2 weeks of the closed loop admissions. Use of topical glucocorticoids is allowable as long as affected skin area does not overlap with study device sites.
4. Subjects using herbal supplements will be excluded, due to the unknown effects of these supplements on glucose control
5. History of hypoglycemic seizure within last 3 months
6. Female subjects who are pregnant, lactating, or unwilling to be tested for pregnancy

• Jennifer Sherr, MD, PhD, Principal investigator, Yale University

NIH grants: T32DK063703