Obstructive sleep apnea and silent cerebral infarction in hypertensive individuals

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Obstructive sleep apnea syndrome (OSAS) is a major public health problem, with a high prevalence in the general population (Lyons Owen and Ryan, 2015). In a study conducted in Spain, Durán et al. (2001) found OSAS in 19% of men and 15% of women from a cohort of subjects aged 30–70 years; this prevalence increases with age in both genders and it is doubled for each passing decade.
The prevalence of OSAS in hypertensive individuals is even higher than that observed in the general population (Calhoun and Harding, 2010), reaching a mean prevalence of approximately 50% (Drager et al., 2010; Silverberg and Oskenberg, 2001).
There are many epidemiological studies (Floras, 2015) showing that OSAS is an independent risk factor for developing hypertension. According to the prospective Wisconsin Sleep Cohort Study (Peppard et al., 2000), the presence of sleep apnea at baseline produced a significantly increased risk of developing hypertension 4 years later, after taking into account hypertension status at baseline, age, gender, body mass index (BMI), neck and waist circumference, weekly use of alcohol and cigarettes. The hazard ratio was 2.89 [95% confidence interval (CI) 1.41–5.64] for those with an apnea–hypopnea index (AHI) > 15 compared with subjects without apnea (Peppard et al., 2000).
Obstructive sleep apnea syndrome is also associated with an increased risk of ischaemic stroke (Campos‐Rodríguez et al., 2014; Ferre et al., 2013; Redline et al., 2010). Nowadays it is known that approximately 8–28% of the healthy population has cerebral ischaemic lesions (silent cerebral infarcts or SCI) found as incidental findings in neuroimaging studies, mainly cerebral magnetic resonance imaging (MRI; Das et al., 2008; DeCarli et al., 2005; Kohara et al., 2003; Price et al., 1997; Schmidt et al., 2004, 2006; Vermeer et al., 2002; Ylikoski et al., 1995) performed in asymptomatic patients. Their detection is important because they are associated with the risk of stroke and subsequent cognitive impairment (Vermeer et al., 2003).
The most well‐known risk factors for SCI are age and arterial hypertension. However, their relationships with other traditional risk factors for stroke are not so clear, and there may be factors not yet fully elucidated that can determine their occurrence. OSAS, given its high prevalence in hypertensive patients, could be potentially associated with SCI and subsequent stroke. However, independent effects of OSAS in relation to the presence of SCI have not been clearly established. There have been only a few studies evaluating the presence of SCI in patients with OSAS (Cho et al., 2013; Davies et al., 2001; Eguchi et al., 2005; Nishibayashi et al., 2008). In two studies conducted in Asia (Cho et al., 2013; Nishibayashi et al., 2008), clear associations were found between SCI and OSAS, although it should be emphasized that the Asian population has an increased risk of OSAS (Li et al., 1999), and these data may not be fully extrapolated to the European population. It is noteworthy that in the study of Nishibayashi et al. (2008), OSAS was associated with the lacunar subtype of SCI, and Cho et al. (2013) also found a significant association with lacunar SCI in patients over 65 years old. Therefore, OSAS might be a particularly relevant risk factor for lacunar SCI, which is the most common subtype of stroke in arterial hypertension.
The aim of this study is to estimate the frequency of OSAS in hypertensive patients with and without SCI in the Spanish population, and to assess whether OSAS is an independent risk factor for developing SCI in hypertensive patients, with special emphasis on lacunar subtype.

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