Sleep-disordered breathing means sleep disorders that involve difficulty breathing during sleep. It refers to momentary, often cyclical, cessations in breathing rhythm (apneas) or momentary or sustained reductions in the breath amplitude (hypopneas), sufficient to cause significant arterial hypoxemia and hypercapnia. These apneas and hypopneas are accompanied either by 1) a compromised, often completely closed, extra-thoracic upper airway (“obstructive” event); 2) a marked reduction or cessation of brain stem respiratory motor output (“central” event); or 3) a combination of central and obstructive events. Symptoms of OSA can be classified into those manifesting during sleep and those present during awake fullness. Several methods had been designed to evaluate the upper airway and to investigate the severity and location of its obstruction.