Obstructive Sleep Apnea (OSA) By Kingman P Strohl, MD, Case School of Medicine, Case Western Reserve University Reviewed / Revised Oct 2022 View Patient Education Pathophysiology Etiology Symptoms and Signs Diagnosis Prognosis Treatment Key Points More Information Topic Resources Body Mass Index (Quetelet's... Epworth Sleepiness Scale (ESS) Obstructive sleep apnea (OSA) consists of multiple episodes of partial or complete closure of the upper airway that occur during sleep and lead to breathing cessation (defined as a period of apnea or hypopnea > 10 seconds) followed by arousals and hyperpnea.