Obstructive Sleep Apnea and the Metabolic Syndrome: Pathophysiological and Clinical Evidence

Obstructive sleep apnea syndrome (OSAS) is a common nocturnal disorder characterized by the presence of repetitive apnea and hypopnea during sleep, daytime sleepiness, and cardiopulmonary dysfunction. Patients with OSAS experience recurrent episodes of cessation of breathing that expose the cardiovascular system to cycles of hypoxia, exaggerated negative intrathoracic pressure, and arousals. The number of apneas and hypopneas per hour of sleep is termed the apnea-hypopnea index (AHI) and has been used as a marker of OSA severity. An OSA disorder is generally defined as five or more apneas or hypopneas per hour of sleep. Moderate and severe OSA are defined as AHI ≥ 15 and ≥30, respectively.