Adult obstructive sleep apnoea (OSA) is associated with cognitive dysfunction. While many review articles have attempted to summarize the evidence for this association, it remains difficult to determine which domains of cognition are affected by OSA. This is because of marked differences in the nature of these reviews (e.g. many are unsystematic) and the many different tasks and domains assessed. This paper addresses this issue by comparing the results of only systematic reviews or meta-analyses assessing the effects of OSA on cognition, the relationship between OSA severity and cognition, and/or the effects of treatment on cognition in OSA. Electronic databases and hand-searching were undertaken to select reviews that reported on these areas. We found 33 reviews; five reviews met predetermined, stringent selection criteria. The majority of reviews supported deficits in attention/vigilance, delayed long-term visual and verbal memory, visuospatial/constructional abilities, and executive function in individuals with OSA. There is also general agreement that language ability and psychomotor function are unaffected by OSA. Data are equivocal for the effects of OSA on working memory, short-term memory and global cognitive functioning. Attention/ vigilance dysfunction appears to be associated with sleep fragmentation and global cognitive function with hypoxaemia. Continuous positive airway pressure treatment of OSA appears to improve executive dysfunction, delayed long-term verbal and visual memory, attention/vigilance and global cognitive functioning. In order to improve our understanding of cognitive dysfunction in OSA, future research should pay particular attention to participant characteristics, measures of disease severity and choice of neuropsychological tests.

Obstructive sleep apnea (OSA) is a nocturnal breathing disorder that is associated with cognitive impairment. The primary determinants of cognitive deficits in OSA are thought to be sleep disruption and blood gas abnormalities. Cognitive impairment is also seen in other disorders that are characterised primarily by sleep disturbance (e.g., sleep restriction/deprivation, insomnia) or hypoxia/hypercarbia (e.g., chronic obstructive pulmonary disease (COPD)). Assessment of the cognitive deficits observed in these other disorders could help better define the mechanisms underlying cognitive deficits in OSA. This study utilised meta-review methodology to examine the findings from systematic reviews and meta-analyses of the effects of untreated OSA, COPD, insomnia, and sleep deprivation on cognitive function in adults, compared with norms or controls. Eighteen papers met inclusion criteria: seven in OSA, two in insomnia, five in COPD, and four in sleep deprivation. OSA and COPD were both accompanied by deficits in attention, memory, executive function, psychomotor function, and language abilities, suggesting that hypoxia/hypercarbia may be an important determinant of deficits in these domains in OSA. Both OSA and sleep deprivation studies were accompanied by deficits in attention and memory, suggesting that short-term sleep disturbance in OSA may contribute to deficits in these domains. Visuospatial deficits were unique to OSA, suggesting the contribution of a mechanism other than sleep disturbance and hypoxia/hypercarbia to this problem. Our findings suggest that the cognitive deficits associated with untreated OSA are multidimensional, with different physiological disturbances responsible for differing cognitive problems.

This meta-analysis suggests that hearing impairment is associated with cognitive problems. However, due to diversity within studies, small sample sizes, the failure to control for premorbid and other health factors, this conclusion may be premature.

Executive function is impaired across all five domains in OSA; these difficulties improved with CPAP treatment. Age and disease severity did not moderate the effects found; however, further studies are needed to explore the extent of primary and secondary effects, and the impact of age and premorbid intellectual ability (cognitive reserve).