Obstructive Sleep Apnea (OSA) -- also called Obstructive Sleep Apnea syndrome -- occurs when there are repeated episodes of complete or partial blockage of the upper airway during Sleep. During an obstructive sleep apnea episode, the diaphragm and chest muscles work harder to open the obstructed airway and pull air into the Lungs. Breathing usually resumes with a loud gasp, snort, or body jerk. These episodes can interfere with sound Sleep. They can also reduce the flow of oxygen to vital organs and cause irregular heart rhythms.