Influence of obstructive sleep apnea on cognitive impairment in patients with COPD.

We read with great interest the recent article in CHEST (December 2012) by Villeneuve et al 1 entitled “Mild Cognitive Impairment in Moderate to Severe COPD: A Preliminary Study.” In their article, Villeneuve et al 1 demonstrated that 36% of patients with COPD had mild cognitive impairment (MCI), compared with 12% of healthy subjects. The authors took great care to exclude from the study all patients who presented comorbidities that could affect cognitive function. With regard to the comorbidities associated with COPD, we would like to highlight the important role of obstructive sleep apnea (OSA). Indeed, it was appreciated by several well-controlled epidemiologic studies that about 20% of subjects with OSA will have COPD, 2 and about 10% of OSA is disclosed among patients with COPD independently of the degree of functional status. 3 There is evidence that OSA has an active role in the development of cognitive impairment. 4 In this regard, in the study of Villeneuve et al, 1 an intriguing fi nding is the slight (although not significant) increase in the Epworth Sleepiness Scale among patients with COPD and MCI compared with patients with COPD but without MCI, which may lead one to hypothesize the presence of a proportion of patients with OSA among subjects with COPD and MCI. The primary mechanisms underlying cognitive impairment in OSA are represented by nocturnal hypoxemia, sleep fragmentation, and daytime sleepiness 4 ; large studies suggest that hypoxemia is responsible for frontal impairment and executive dysfunction, while sleep fragmentation and daytime sleepiness infl uence attention. 4 In patients with COPD, hypoxemia, hypercapnia, and vascular comorbidities may be a cause of cognitive alterations. 1 Therefore, in patients with COPD and OSA (overlap syndrome), there is the possibility that all the aforesaid mechanisms operate simultaneously and/or synergistically. In this regard, it is widely accepted that patients with overlap syndrome develop more pronounced, nocturnal, oxygen desaturation than those with COPD or OSA alone. 3 Furthermore, there is evidence that subjects with overlap syn drome show more severe diurnal hypoxemia compared with patients with OSA. 5 For all these reasons, we would like to stimulate discussion about the need to consider the presence of OSA among patients with COPD who have cognitive impairment.