Central sleep apnea - reduced central respiratory drive to the diaphragm during sleep. Reduced muscle tone in non-REM sleep leads to reduction of airways → further worsened in REM sleep → Blood oxygen level ↓ (hypoxia) and carbon dioxide level ↑ (hypercapnia) → waking the pts.
Obstructive sleep apnea — excessive relaxation of the pharyngeal muscles occludes the airways, (especially in obese pts).
Both forms of apnea lead to insomnia and sleepiness during normal waking periods. In severe cases, there is intellectual impairment - possibly due to loss Of REM sleep.
Narcolepsy
Definition: excessive daytime sleepiness. There may be "attacks" of REM sleep /w cataplexy (muscular paralysis).
Mechanism: pts have <10% of hypothalamic hypocretin neurons → ↓ orexin/hypocretin neurons activity → ↓ arousal during day time;