244 Physical fitness attenuates the deleterious association of sleep apnea with gray matter volume in the Wisconsin Sleep Cohort Study

Abstract

Introduction: Recent evidence has illustrated that gray matter (GM) atrophy, a diagnostic hallmark of Alzheimer's disease (AD), may be influenced by psychosocial risk modifiers such as physical exercise and sleep. Cardiorespiratory fitness, a measure of oxygen delivery and utilization during exercise, is positively associated with both sleep quality and gray matter volume in brain areas associated with age-related cognitive decline, such as the hippocampus. In contrast, sleep apnea has been linked to global and regional gray matter atrophy, which is thought to be driven in-part by the incomplete modulation of cardiovascular and respiratory control during sleep. This study examines whether cardiorespiratory fitness modifies the deleterious relationship between sleep apnea and GM volume in a sample of non-demented older participants from the Wisconsin Sleep Cohort (WSC). Methods: Using data from a subset of WSC participants (n=129, 51% female, mean [range] age at baseline=68 [49-85] years), cardiorespiratory fitness was estimated using a Non-Exercise CardioRespiratory Fitness Measure (NECRFM; based on age, sex, BMI, self-reported physical activity, and resting heart rate). Sleep apnea severity was measured by overnight polysomnography and characterized by the base 10 logarithm of the apnea-hypopnea index, log10(AHI+1). We assembled cross-sectional linear models of MRI-measured total GM volume using NECRFM and log10(AHI+1) as predictors while controlling for age, sex, BMI, education, and hypertension. Regional volumetric changes in the hippocampus and amygdala were assessed using analogous linear models, adjusting both outcome volumetrics for total intracranial volume. Results: While the interaction between fitness and apnea severity was not significant (p=0.50), results stratified at the median NECRFM illustrated that among the less fit individuals, higher log10(AHI+1) was associated with a significant reduction in total GM volume (B(SE)=- 0.06 (0.02); p=0.007); this relationship was not significant among those who were more fit (B(SE)=-0.03 (0.02); p=0.11). There were no significant effects in the hippocampus or amygdala. Conclusion: These results indicate that cardiovascular fitness may attenuate the effect of severe sleep apnea on GM volume in older adults, supporting the protective role of cardiovascular fitness in aging brain health.