Basal Insulin Adjustments and Continuous Glucose Monitoring During Exercise in Type 1 Diabetes

Research has demonstrated that the timing, type, duration and intensity of exercise can all impact blood glucose levels differently in patients with type 1 diabetes. Continuous steady state moderate intensity aerobic exercise tends to drop blood glucose levels, while vigorous-to-maximal intensity exercise tends to cause blood glucose levels to rise. The purpose of this dissertation was to test different basal insulin strategies to improve glycemia during various forms of exercise and in recovery in patients with type 1 diabetes on continuous subcutaneous insulin infusion (CSII) therapy. A secondary purpose was to examine the effectiveness of continuous glucose monitor (CGM) technology to track interstitial glucose levels during exercise and in recovery. Initially, we examined the effects of insulin pump suspension on glycemia during aerobic and circuit-based exercise. We found that pump suspension at exercise onset caused a greater drop in glycemia during aerobic vs. circuit-based exercise. Aerobic exercise also modestly increased the time spent in hypoglycemia 12 hours post-exercise. We then investigated the effects of a reduced insulin infusion rate (pump on) vs. pump suspension (pump off) during intermittent high intensity exercise and found neither an advantage nor disadvantage on blood glucose level with pump removal for exercise. Interestingly, pump on resulted in slightly higher time spent in hypoglycemia in the 12-hour period post-exercise vs. pump off. In a third study, we tested the strategy of lowering basal insulin delivery by 50% or 80% well in advance of exercise vs. pump suspension at exercise onset in an attempt to reduce hypoglycemia risk. Overall, we found that a 50-80% basal rate reduction set 90 mins pre-exercise attenuated the drop in blood glucose level better than pump suspension at exercise start. Finally, we assessed CGM accuracy during exercise and in the meal post-exercise and found that CGM underestimated the drop in glycemia during exercise and appeared to lag behind self-monitoring blood glucose values when glycemia was changing rapidly. This thesis dissertation highlights a number of novel strategies, including basal insulin rate reductions and altering the type of exercise for improved exercise management in people living with type 1 diabetes on CSII.