Abstract
Obstructive sleep apnea (OSA) is characterized by recurrent upper airway blockage, with continued diaphragmatic efforts to breathe during sleep. Brain structural changes in OSA appear in various regions, including white matter sites that mediate autonomic, mood, cognitive, and respiratory control. However, the relationships between brain white matter changes and disease severity in OSA are unclear. Our aim was to examine associations between an index of tissue integrity, magnetization transfer (MT) ratio values, which show MT between free and proton pools associated with tissue membranes and macromolecules, and disease severity [apnea-hypopnea index (AHI)] in OSA subjects. We collected whole-brain MT imaging data from 19 newly-diagnosed, treatment-naïve OSA subjects [age, 50.4±8.6 years; 13 males; AHI, 39.7±24.3 events/hour], using a 3.0-Tesla MRI scanner. Using these data, whole-brain MT ratio maps were calculated, normalized to common space, smoothed, and correlated with AHI scores using partial correlation analyses (covariates; age, gender; p<0.005). Multiple brain sites in OSA subjects, including superior and inferior frontal regions, ventral medial pre-frontal cortex and nearby white matter, mid-frontal white matter, insula, cingulate and cingulum bundle, internal and external capsules, caudate nuclei and putamen, basal forebrain, hypothalamus, carpus callosum, and temporal regions showed principally-lateralized negative correlations (p<0.005). These regions showed significant correlations even with correction for multiple comparisons (cluster-level, family wise error, p<0.05), except for a few superior frontal areas. Predominately negative correlations emerged between local MT values and OSA disease severity, indicating potential usefulness of MT imaging to examine the OSA condition. The findings indicate that OSA severity plays a significant role in white matter injury.
The magnetization transfer imaging procedure shows white matter injury increases with disease severity (apnea-hypopnea index) in obstructive sleep apnea (OSA) subjects, suggesting a role of disease severity in white matter changes. The findings also indicate that method can be used in OSA and other neurological conditions to monitor disease progression.
