Editing Sleep apnea (section)

==Mechanism==
'''Obstructive sleep apnea'''

The causes of obstructive sleep apnea are complex and individualized, but typical risk factors include narrow pharyngeal anatomy and craniofacial structure.<ref name="Osman-2018"/> When anatomical risk factors are combined with non-anatomical contributors such as an ineffective pharyngeal dilator muscle function during sleep, unstable control of breathing (high loop gain), and premature awakening to mild airway narrowing, the severity of the OSA rapidly increases as more factors are present.<ref name="Osman-2018"/> When breathing is paused due to upper airway obstruction, carbon dioxide builds up in the bloodstream. [[Chemoreceptor]]s in the bloodstream note the high carbon dioxide levels. The brain is signaled to awaken the person, which clears the airway and allows breathing to resume. Breathing normally will restore oxygen levels and the person will fall asleep again.<ref>{{cite book |last=Green |first=Simon |title=Biological Rhythms, Sleep and Hyponosis |date=8 February 2011 |publisher=Palgrave Macmillan |isbn=978-0-230-25265-3 |location=England |page=85}}</ref> This carbon dioxide build-up may be due to the decrease of output of the brainstem regulating the chest wall or pharyngeal muscles, which causes the [[pharynx]] to collapse.<ref name="Pur20182">{{cite book |last=Purves |first=Dale |title=Neuroscience |date=4 July 2018 |publisher=Oxford University Press |isbn=978-1-60535-380-7 |edition=Sixth |location=New York |oclc=990257568}}{{page needed|date=March 2021}}</ref> As a result, people with sleep apnea experience reduced or no [[slow-wave sleep]] and spend less time in [[REM sleep]].<ref name="Pur20182" />

'''Central sleep apnea'''

There are two main mechanism that drive the disease process of CSA, sleep-related hypoventilation and post-hyperventilation [[hypocapnia]].<ref name="Badr-2019"/> The most common cause of CSA is post-hyperventilation hypocapnia secondary to heart failure.<ref name="Badr-2019" /> This occurs because of brief failures of the ventilatory control system but normal alveolar ventilation.<ref name="Badr-2019" /> In contrast, sleep-related hypoventilation occurs when there is a malfunction of the brain's drive to breathe.<ref name="Badr-2019" /> The underlying cause of the loss of the wakefulness drive to breathe encompasses a broad set of diseases from strokes to severe [[kyphoscoliosis]].<ref name="Badr-2019" />