0612 WHITE MATTER DIFFUSIVITY CHANGES WITH INTERMITTENT HYPOXEMIA IN OBSTRUCTIVE SLEEP APNEA

Abstract

Cerebral white matter is especially vulnerable to hypoxic damage, and thus, may be affected by nocturnal repetitive hypoxemia that is characteristic of obstructive sleep apnea (OSA). Mean diffusivity (MD) can serve as a marker of cerebral white matter integrity, and has been observed to decrease in the acute stage of an ischemic stroke and to increase in the chronic stage. Therefore, the association between MD and nocturnal hypoxemia severity was evaluated to understand how OSA affects the brain, and more specifically cerebral white matter integrity. Sixty-six subjects (mean age: 65.1 ± 6.2 y/o, 55–82 y/o) representing a wide spectrum of nocturnal hypoxemia underwent a polysomnographic recording and a magnetic resonance imaging session including a sequence of diffusion weighted imaging. The apnea-hypopnea index ranged from 0 to 67.3 events/hour of sleep. Minimal oxygen saturation (73–94%), sleep time with oxygen saturation <90% (0–95 min), and index of oxygen desaturation >3% (0–41 events/hour of sleep) were used to evaluate intermittent hypoxemia. Using Tract-Based Spatial Statistics within FSL, MD was estimated. Correlations adjusted for age were performed between intermittent hypoxemia and MD in all voxels of the white matter skeleton (p<0.05 corrected for multiple comparisons). The index of oxygen desaturation >3% correlated significantly with decreased MD in several white matter tracts. Most of these reductions were observed in the bilateral corticospinal tracts, bilateral fronto-parietal superior longitudinal fascicles as well as the corpus callosum. No association was found between the minimal oxygen saturation or sleep time with oxygen saturation <90% with cerebral white matter MD. Decreased MD in several cerebral white matter tracts was associated with the index of oxygen desaturation. The frequency rather than the intensity of hypoxemia is associated with decreased MD, suggesting white matter alterations similar to what is observed acutely in ischemic injuries. The impact of this possible white matter damage on cognitive health in older individuals with OSA is currently being investigated. Canadian Institutes of Health Research (CIHR), Fonds de Recherche du Québec en Santé (FRQ-S).