Obstructive sleep apnea (OSA) is characterized by repetitive episodes of complete and partial obstructions of the upper airway during sleep. The diagnosis of OSA requires the objective demonstration of abnormal breathing during sleep by measuring the respiratory disturbance index (RDI, events per hour of sleep), i.e. the frequency of apnea (complete upper airway obstruction), hypopnea (partial upper airway obstruction) and arousals from sleep related to respiratory efforts. OSA is defined by combining symptoms and an RDI ≥5 or by an RDI ≥15 without symptoms. The apnea-hypopnea index (AHI), the frequency of apnea and hypopnea events per hour of sleep, is widely used to define OSA (many clinical and epidemiological studies use this metric). In the general adult population, the prevalence of OSA defined by ≥5 apnea and hypopnea events per hour of sleep associated with excessive sleepiness is approximately 3-7% in men and 2-5% in women. The prevalence of OSA is much higher, e.g. ≥50%, in patients with cardiac or metabolic disorders than in the general population. Risk factors for OSA include obesity (the strongest risk factor), upper airway abnormalities, male gender, menopause and age (the prevalence of OSA associated with a higher risk of morbidity and mortality increases with age and peaks at approximately 55 years of age). OSA is associated with symptoms during sleep (snoring, choking and nocturia) and wakefulness (excessive sleepiness, fatigue and lack of energy) and with sequelae such as psychological changes, alterations in the quality of life, and social, familial and professional performance including vehicle and industrial accidents. The identification of OSA may be a difficult task for the clinician, even in populations in which OSA is highly prevalent such as patients with cardiovascular disorders because they may not present the cardinal signs of the disease, e.g. excessive sleepiness and obesity. Guidelines have been developed to tailor OSA therapy to patients according to the results of their disease evaluation and their preferences.
