Obstructive sleep apnoea in older adults: Predictors of cognitive decline and neurodegeneration

Abstract

There is growing evidence that sleep disturbances share associations with neurodegeneration, and poor sleep is emerging as an independent risk factor for dementia. As a common sleep disorder, obstructive sleep apnea (OSA) has been connected to compromised cognition, brain integrity and an increased risk for dementia. However, there is a need to clarify these relationships in older adults and understand the mechanisms underpinning the link between OSA and cognitive decline. The aims of this thesis were: 1) to characterise and quantitatively analyse the relationship between OSA and cognitive function in older adults, 2) to determine whether any changes in neural oscillations during sleep or brain grey matter thickness and volume, might be associated with OSA and related to makers of cognitive decline (e.g. memory) in a sample of older adults at-risk for dementia. At-risk adults were diagnosed as health-seeking older adults (>50 years) with subjective or objective cognitive impairment. Neural oscillations were recorded using electroencephalography and brain grey matter thickness and volume were measured using magnetic resonance imaging. These findings showed that the presence of OSA in at-risk older adults is related to a marked reduction in specific neural oscillations (sleep spindles), key aspects of sleep microarchitecture that are integrally linked with memory consolidation. Furthermore, OSA-related oxygen desaturation was associated with decreased cortical thickness in both the left and right temporal lobes, while sleep disturbance was related to increased cortical thickness in in frontal, central and occipital regions of the right cortex. This work has provided evidence that OSA is related to features which may contribute to early-stage neurodegeneration and cognitive decline, which are important in identifying critical periods for intervention. Given that effective treatment exists for OSA, efforts to increase OSA screening in older adults are now warranted.