388 Sleep-Wake Disorders
can be present. With progression of ventilato ry insufficiency, bloo d gas abnormalities ex-
tend into wakefulness. Features of the me dical condition causing sleep-related hypoven-
tilation can also be present. Episodes of hy poventilation may be as sociated with frequent
arousals or bradytachycardia. Individuals ma y complain of excessive sleepiness and in-
somnia or morning headaches or may present wi th findings of neuroc ognitive dysfunction
or depression. Hypoventilation may not be present during wakefulness.
Prevalence
Idiopathic sleep-related hypoventilation in adults is very uncommon. The prevalence of
congenital central alveolar hy poventilation is unknown, but the disorder is rare. Comor-
bid sleep-related hypoventilation (i.e., hypo ventilation comorbid with other conditions,
such as chronic obstructive pulmonary diseas e [COPD], neuromuscular disorders, or obe-
sity) is more common.
Development and Course
Idiopathic sleep-related hypove ntilation is thought to be a slowly progressive disorder of
respiratory impairment. When th is disorder occurs comorbidly  with other disorders (e.g.,
COPD, neuromuscular disorders, obesity), diseas e severity reflects the severity of the un-
derlying condition, and the disorder progre sses as the condition worsens. Complications
such as pulmonary hypertension, cor pulmon ale, cardiac dysrhythmias, polycythemia,
neurocognitive dysfunction, and worsening re spiratory failure can develop with increas-
ing severity of blood gas abnormalities. 
Congenital central alveolar hypoventilation  usually manifests at birth with shallow,