BACKGROUND: Obstructive sleep apnea (OSA) is a common sleep disorder that is marked by recurrent collapse of the oropharyngeal airway during sleep. The collapsed airway causes cessation of airflow and leads to intermittent hypoxia and disruption of the normal sleep pattern. Risk factors for sleep apnea include obesity, male sex, abnormalities of the upper airway (e.g. short mandible, tonsillar hypertrophy, adenoid hypertrophy), and increasing age. Symptoms of OSA include snoring, daytime sleepiness, restless sleep, choking or gasping during sleep, and poor concentration.

OSA is diagnosed with a sleep study. During the study, airflow is monitored through nasal prongs that the patient wears while they sleep. Decreases in airflow known as apneas and hypopneas are counted. An apnea is defined as a total cessation or near cessation of airflow lasting at least 10 seconds. A hypopnea is a reduction in airflow (≥ 30% from baseline) that lasts at least 10 seconds. The apnea-hypopnea index (AHI) is the total number of apneas and hypopneas divided by the total sleep time in hours. An AHI of 5 - 15 is classified as mild OSA, an AHI of 15 - 30 is classified as moderate OSA, and an AHI of > 30 is classified as severe OSA.

OSA is most often treated with a device called a CPAP machine. A CPAP (continuous positive airway pressure) device consists of a mask that fits over the nose or nose and mouth. The mask is attached to a machine that delivers continuous pressure through the mask. The continuous pressure helps prevent the airway from collapsing during sleep. In trials, CPAP use has been shown to reduce systolic blood pressure by 2 - 3 mmHg in patients with normal blood pressure and by 6 - 7 mmHg in patients with resistant hypertension. Observational studies have found a decreased risk for cardiovascular events in patients with OSA who were treated with CPAP. The SAVE study (Study 1) detailed below is the first randomized controlled trial to evaluate the effects of CPAP on cardiovascular outcomes in patients with OSA. The study below it (Study 2) looked at the effects of an implantable device on OSA in a cohort of patients.
Study 1
Study 2