Autonomic Function in Obstructive Sleep Apnea

The purpose of this study is to determine if obstructive sleep apnea (OSA)-a condition in which respiration and oxygenation are affected during sleep-can cause abnormal autonomic function and blood sugar (glucose) processing, which could lead to diabetes, or pre-diabetic conditions. The autonomic system controls heart rate, blood pressure, breathing, and other functions of the body. OSA and diabetes are commonly found in overweight individuals and both can cause increased risk of heart disease and strokes. OSA can be treated using nasal continuous positive airway pressure (CPAP) which overcomes the obstruction to airflow that occurs in OSA. In this study, the scientists hope to determine if individuals with OSA have an increased prevalence of undiagnosed diabetes or pre-diabetic conditions, and if autonomic abnormalities observed previously in OSA are more severe or more common in people with OSA and diabetes or pre-diabetic conditions. Participants will undergo a sleep study and glucose studies to determine if they have sleep apnea and impaired fasting glucose, impaired glucose tolerance, or undiagnosed diabetes (collectively called impaired glucose regulation). Individuals with sleep apnea with and without glucose abnormalities will be age and BMI matched, and will undergo further autonomic and peripheral nerve testing. Individuals without diabetes will be followed for one year of CPAP treatment for their sleep apnea-with visits at 3 month intervals to evaluate glucose and autonomic function. Individuals without sleep apnea or diabetes will also undergo autonomic and peripheral nerve testing. Participants will also complete questionnaires to assess their sleepiness and symptoms of autonomic function. Results from this study will help researchers determine if abnormalities of autonomic function seen in people with OSA are caused by OSA or by coexistent impaired glucose regulation present in people with OSA. In addition, results from the study will show if CPAP treatment improves autonomic dysfunction by correcting breathing abnormalities, or by secondary improvement of glucose regulation.