Risk of Cognitive Impairment by Sleep-Disordered Breathing

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Lam et al1 conducted a systematic review on the association between sleep-disordered breathing (SDB) and cognitive impairment and also summarized cognitive outcomes of elderly patients treated with continuous positive airway pressure (CPAP) with special reference to postoperative delirium. After overviewing 15 studies on the relationship between SDB and cognitive impairment, and 5 studies on the effect of CPAP on cognitive impairment, they recognized a positive relationship between SDB and cognitive impairment. In addition, CPAP treatment was effective for the improvement of cognitive impairment. I have some concerns about their study.
First, the authors did not conduct a meta-analysis on the relationship. Leng et al2 conducted a meta-analysis on the relationship between SDB, risk of cognitive impairment, and cognitive domains. Pooled risk ratio (95% confidence interval [CI]) of SDB for cognitive impairment was 1.26 (1.05–1.50). In addition, standard mean difference (95% CI) of SBD for executive function was −0.05 (−0.09 to 0.00). The selected prospective studies differed from those by Lam et al,1 and caution should also be paid that Lam et al selected subjects aged 40 or older, which was relatively younger than those by Leng et al.2
Second, Yaffe et al3 reported a prospective study to determine contributors to cognitive impairment in patients with SDB. Odds ratio (95% CI) of SDB for the development of cognitive impairment being 1.85 (1.11–3.08) adjusted by age, body mass index, education level, presence of diabetes mellitus, and baseline cognitive scores. There are several common risk factors between cognitive impairment and SDB, and statistical model is important for selecting independent variables. In addition, Kerner and Roose4 reported a mechanism underlying the association between SDB and cognitive impairment with special reference to cerebral microvascular and neurovascular system. The effect of SDB on cognitive impairment should be evaluated by stratifying the type of predementia.
Finally, the effect of CPAP on the improvement of cognitive impairment has been reviewed,5 although there was a lack of meta-analysis. In addition, dose–response relationship between SDB and cognitive impairment should be evaluated with a sufficient number of prospective studies. Sex, age, severity, and duration of SDB would affect subsequent development of cognitive impairment.
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