Metabolic Impact of Intermittent CPAP

Obstructive sleep apnea is a risk factor for diabetes and cardiovascular disease, by unknown mechanisms. The investigators hypothesize that sleep apnea changes glucose and lipid metabolism during sleep, which over time could lead to diabetes and cardiovascular disease. This study examines metabolic changes during sleep in patients with obstructive sleep apnea. Patients accustomed to continuous positive airway pressure (CPAP) therapy are enrolled to undergo sleep studies, either on CPAP therapy or after withdrawing from CPAP for 3 nights. During sleep, blood samples are obtained so that metabolic function can be compared between sleep apnea and CPAP nights.

Inclusion Criteria: * History of moderate to severe Obstructive sleep apnea (OSA) (AHI or respiratory disturbance index (RDI)\> 10). * They must also own a CPAP machine and report the ability to tolerate sleeping with or without CPAP during the night. Exclusion Criteria: * Uncontrolled hypertension with systolic blood pressure \>170 or diastolic blood pressure \> 110 * Congestive heart failure * Use of clonidine or nicotinic acid medication * Diabetes requiring the use of insulin * Known pregnancy, by urine testing in women of child-bearing age * History of falling asleep while driving, near miss * High risk occupation (pilot, commercial driver) * Hemoglobin \< 10 g/dL on point of care screening