The major findings of this study were that more than one-half of a cohort of hypertensive primary care patients had objective evidence of OSA. But no relationship between OSA and severity of blood pressure elevation, or specific comorbid conditions was seen. Diabetes, depressive symptoms, insomnia, and EDS were common, but not associated with OSA. Male gender, BMI >30 kg/m2, snoring, witnessed apnoeas, and sleep duration >8 hours were significant correlates of OSA.
OSA in this sample was more common than that found in community-based Scandinavian and European general populations [3–5
] despite our focus on the occurrence of undiagnosed OSA (e.g. patients with treated OSA were excluded). This could be explained by our selection of hypertensive patients [8
]. Sjöström et al. [11
] found in a stratified sample of hypertensive men that 37% had AHI >10. In a community-based case-control study, Hedner et al. [12
] found AHI > 10 in 83% of middle-aged patients with both HT and diabetes. Comparing our data with those from these studies is difficult, since they used different cut-off scores for AHI and Hedner's subjects also had metabolic syndrome, one of the best predictors for OSA [13
Prior studies [20–22
] have suggested that OSA is commonly associated with HT. We found no association between OSA severity and level of blood pressure elevation or pharmacological treatment, in contrast to previous studies where a dose–response relationship was found between night-time blood pressure and increasing AHI [23
]. This may be due to the fact that our patients were already treated for HT, mostly successfully. EDS and depressive symptoms, commonly assumed as predictors of OSA [13
], were not associated with OSA although we used validated questionnaires to assess them [16
]. The fact that we did not enrol patients from a sleep clinic might explain the lower occurrence of sleeping difficulties, EDS, and depressive symptoms found compared with other samples [13
]. These findings shed light on the difficulties that GPs have in identifying patients with OSA in primary care who are in need of weight reduction or treatment of OSA [24
]. However, we identified that hypertensive men who are obese (i.e. BMI > 30 kg/m2), snore, and report witnessed apnoeas, as well as long sleep duration (i.e. >8 hours) can be suspected to have OSA. Obesity is common in sleep clinic patients [8
], and intensive interventions based on low-calorie diets to reduce weight have been shown to decrease AHI [26
], but long-term results are lacking. Questionnaires, such as the BSAQ [14
], focusing on weight gain/obesity, snoring, witnessed apnoeas, and EDS may, together with simple two-channel recording devices [28
], be suitable in routine screening in primary care settings. Importantly, results from the BSAQ and the two channel devices are not comparable to validated diagnostic tools, such as polygraphy or polysomnography, and need to be more thoroughly evaluated regarding sensitivity and specificity. Large, well- designed studies are therefore needed to explore symptom profiles, clinical characteristics, and different suitable screening procedures for hypertensive patients with undiagnosed OSA of different severity levels in primary care settings. Such studies can help to identify patients who would benefit from referral to a sleep clinic.
We found that desaturations were highly prevalent (i.e. mean ODI of 32.0) in those with AHI > 15. Hypoxia is an important contributor to CVD in patients with OSA (i.e. by sympathetic activation and increased levels of catecholamines, causing inflammation, arterial stiffness, and atherosclerosis) [6
]. Initiation of continuous positive airway pressure (CPAP) can eliminate apnoeas and desaturations, and reduce cardiovascular morbidity and mortality [29
], particularly in patients with severe OSA and daytime symptoms. Blood pressure reductions after CPAP have been found, especially in sleepy patients with frequent desaturations, but also when HT is severe, untreated, or refractory [30
]. However, the effect of CPAP in hypertensive primary care patients with OSA, especially those with mild and moderate OSA, is unknown.
In conclusion, undiagnosed OSA (AHI > 15) is common in hypertensive primary care patients. Snoring male patients with elevated BMI, long sleep duration, and witnessed apnoeas should be investigated for OSA. Future studies should focus on randomized controlled trials evaluating long-term effects of CPAP in hypertensive primary care patients with OSA. Stratifying men and women with different levels of OSA will strengthen the evidence base for treatment. Potential confounding factors for CVD, such as obesity, should also be controlled.
Limitations of this study include the cross- sectional design, and the lack of a normotensive control group matched for age, gender, and BMI, as well as the relatively low participation rate. Furthermore, no objective data regarding sleep were collected, which means that the occurrence of OSA might have been even higher since there are difficulties in estimating sleep onset and wake-up time with polygraphy [28