What we don't know about sleep-related breathing disorders in the elderly.

IN THIS ISSUE OF SLEEP, SFORZA, ROCHE, AND COLLEAGUES 1 PRESENT CROSS-SECTIONAL DATA EXAMINING THE ASSOCIATION BETWEEN COGNITIVE function and sleep-related breathing disorders (SRBD) in 827 healthy elderly subjects. An extensive assessment including clinical interview, neurological examination, 12-lead ECG, ECG Holter, and magnetic resonance imaging excluded those with myocardial infarction, previously diagnosed sleep disorders, stroke, dementia, and other cardiac and neurological disorders from the cohort at study entry. Two years after enrollment, 827 (58.5% women, mean age 68 years) of the original cohort had one night of nocturnal unattended at home polygraphy, self-assessed cognitive difficulties in everyday life, depression, anxiety, and daytime sleepiness, and an extensive neuropsychological battery of primarily memory and executive function testing. Noteworthy findings were: (1) 53.8% prevalence of SRBD, defined as apnea + hypopnea index (AHI) > 15; (2) lack of day time sleepiness in the entire group with no significant difference in daytime sleepiness between those with and without SRBD; (3) little hypoxemia in those with SRBD, with no difference in minutes SaO 2 30) demonstrating the lowest scores, but no significant differences in other cognitive function tests; and (6) in multivariate models no significant or strong relationships between cognitive function and severity of SRBD. 1 This study is unique and important, largely because the find ings regarding the relationship between SRBD and cognitive function in healthy older adults were negative on almost every front, with the exception of a consistent deficit in episodic memory. The sample size, strength of the study design, methods, and analysis support the internal consistency and generalizability of the findings. The neuropsychological cognitive function battery was comprehensive, and the measures the investigators used are standard for detecting memory and executive function deficits. Inclusion of another measure of attention, such as the psychomotor vigilance task, may have increased sensitivity to decrements in attention. The approach to data analysis was thoughtful, with targeted bivariate and multivariate analyses to detect differences, if they existed. So here is what we know: in a large population-based sample of healthy 68-year-olds, a comprehensive measure of cognitive function showed that those with SRBD had the same cognitive function (except for a deficit in delayed recall) as those without SRBD. 1 Yet, much remains unknown about SRBD in the elderly. The biggest unknown is the long-term effect of SRBD on cognitive, everyday function, and other common comorbidities such as heart disease in older adults. It is possible that these healthy older adults without cardiac and neurological disease have recent onset SRBD and are thereby without consequent cognitive impairment of significance. We also do not know the earlier severity of SRBD in this sample, further complicating definitive conclusions about short- and long-term effects of SRBD in the elderly. Moreover, if this sample of healthy older adults has had SRBD most of their adult lives, what has protected them from