384 Sleep-Wake Disorders
Note:  See the section “Diagnostic Features” in text.
Specify current severity:
Severity of central sleep apnea is graded according to the frequency of the breathing
disturbances as well as the extent of associated oxygen desaturation and sleep frag-
mentation that occur as a consequence of repetitive respiratory disturbances.
Subtypes
Idiopathic central sleep apnea and Cheyne-Stokes breathing are characterized by increased
gain of the ventilatory contro l system, also referred to as high loop gain,  which leads to in-
stability in ventilation and PaCO2 levels. This instability is termed periodic breathing and
can be recognized by hyperventilation alternating with hypoventilation. Individuals with
these disorders typically have pCO2 levels while awake that are slightly hypocapneic or
normocapneic. Central sleep apnea may also mani fest during initiation of treatment of ob-
structive sleep apnea hypopnea or may occur in association with obstructive sleep apnea
hypopnea syndrome (termed complex sleep apnea ). The occurrence of central sleep apnea in
association with obstructive slee p apnea is also considered to be due to high loop gain. In
contrast, the pathogenesis of central sleep apnea comorbid wi th opioid use has been at-
tributed to the effects of opioids on the re spiratory rhythm generators in the medulla as
well as to its differential effects on hypoxic versus hypercapneic respiratory drive. These
individuals may have elevated pCO2 levels while awake. Individuals receiving chronic
methadone maintenance therapy have been no ted to have increased somnolence and de-
pression, although the ro le of breathing disorders associated with opioid medication in caus-
ing these problems has not been studied. 
Specifiers