Definition Obstructive Sleep Apnea (OSA) is defined as complete apnea for 10 seconds, five times per hour, associated with a 4% decrease in SaO2 (while sleeping). Hypopnea is a less-severe form of obstruction (50% reduction in airflow, also accompanied by a 4% fall in SaO2). Both OSA and hypopnea require a sleep study for diagnosis. […]