Blood Flow of the Middle Cerebral Artery With Sleep-Disordered Breathing: Correlation With Obstructive Hypopneas

Abstract

To the Editor: Netzer et al1 recently reported that obstructive sleep hypopnea and apnea are associated with reductions in middle cerebral artery (MCA) blood flow compared with central sleep apnea. This study may explain the increased incidence of ischemic stroke in obstructive sleep disorders,2 3 4 although it is important to remember that other mechanisms independent of cerebral hemodynamics have also been proposed.5 6 Transcranial Doppler blood flow measurements of the MCA are assumed to reflect total brain flow, but it should be noted that this technique does not evaluate regional cerebral blood flow (CBF). Several lines of evidence suggest that localized disturbances in CBF may be important in patients who sustain cerebrovascular events in association with sleep disorders. Non-REM sleep in normal subjects is associated with a global reduction in brain blood flow (measured by stable xenon computed tomography) and global glucose hypometabolism (measured by positron emission tomography). Against this global fall in CBF are important regional variations, with some brain regions (frontal cortex, basal ganglia, thalamus, pons, cerebellum) affected to a greater degree while others (temporal cortex) are relatively unaffected.7 8 During REM sleep there is increased CBF to the associated visual area, presumably reflecting the activation involved in processing visual dream experiences, with a reduction in inferior frontal cortical flow.9 Preliminary observations in sleep apnea syndromes indicate the presence of focal cortical perfusion abnormalities in the awake or apneic state that are …