Evaluating the Dynamics of Insulin and Non-insulin Mediated Effects on Glucose During Aerobic Exercise in Subjects With Type 1 Diabetes

Detailed Summary

People with type 1 diabetes often find exercise very difficult to manage, because of the high risk for low blood glucose levels. This can occur very quickly once exercise starts and presents many risks for subjects, such as severe symptoms, confusion, passing out, seizures, and even coma or death in very severe cases. Preventing low blood glucose levels during and after exercise is important because physical exercise is a key component of managing diabetes. It is often hard to correctly adjust insulin infusion rates or doses before exercise as the relationship between exercise and changes in glucose levels in those who have type 1 diabetes is still not fully understood. Therefore, the investigators propose this study to further our understanding in this area. This study is designed to help separate the effects of insulin from those of muscle work (non-insulin effects) on the changes in blood glucose levels during aerobic exercise. The main hypothesis is that the non-insulin effects occur quickly during exercise and account for the rapid change in blood glucose levels once aerobic exercise begins. These effects can be separated from the slower changes in insulin sensitivity that occur because of exercise, and which account for reduced insulin demand even after exercise has stopped. The investigators will investigate the effects of both moderate and intense aerobic exercise at different levels of insulin in the body to help separate the insulin and non-insulin effects. The investigators wish to recruit 26 subjects to take part in this study. Subjects will be randomly divided into two groups, with 13 in each group. Group 1 will undergo moderate aerobic exercise, while group 2 will undergo intense aerobic exercise. Each subject will repeat the exercise study three times on three separate days at least 2 weeks apart, while having insulin infused at a low, a medium, and a high rate. Subjects will have an IV line placed in each arm, one for drawing blood relatively frequently during the study, and another for infusion of insulin, glucose, and a special glucose tracer (non-radioactive). Each study lasts about 9 hours. Information from this study will be used to help develop a mathematical model of how glucose changes during exercise in type 1 diabetes. Such a model of type 1 diabetes and exercise will be very useful for adjusting insulin doses in patients who use multiple daily injections of insulin, and can help to guide an automated insulin delivery system, such as the artificial pancreas.

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