Obstructive sleep apnea (
OSA) (or apnoea) is the most common type of
sleep apnea and is caused by complete or partial obstructions of the
upper airway. It is characterized by repetitive episodes of shallow or paused breathing during sleep, despite the effort to breathe, and is usually associated with a reduction in
blood oxygen saturation. These episodes of decreased breathing, called "
apneas" (literally, "without breath"), typically last 20 to 40 seconds.