Symptom profile of undiagnosed obstructive sleep apnoea in hypertensive outpatients in primary care: a structural equation model analysis.

BACKGROUND Obstructive sleep apnoea (OSA) has been linked to hypertension in sleep clinic populations, but little is known about the symptom profile of undiagnosed OSA in hypertensive outpatients in primary care. AIM To explore characteristics associated with undiagnosed OSA in hypertensive primary care patients. METHODS Cross-sectional design, including 411 consecutive patients (52% women), mean age 57.9 years (standard deviation [SD] 5.9 years), with diagnosed hypertension (blood pressure >140/90 mmHg) from four primary care centres. All subjects underwent a full-night, home-based, respiratory recording to establish the presence and severity of OSA. Clinical variables, medication and comorbidities, as well as data from self-rating scales regarding symptoms/characteristics, insomnia, excessive daytime sleepiness, depressive symptoms and health were collected during a clinical examination. Factor analyses and structural equation modelling (SEM) were used to explore the relationships between self-rated symptoms, clinical characteristics and objectively verified diagnosis of OSA. MAIN OUTCOME Measures symptom profile of undiagnosed OSA (as measured by the Apnoea/Hypopnoea Index [AHI]) in hypertensive outpatients in primary care. RESULTS Fifty-nine percent of the patients had an AHI ≥ 5/hour indicating OSA. An exploratory factor analysis based on 19 variables yielded a six-factor model (anthropometrics, blood pressure, OSA-related symptoms, comorbidity, health complaints and physical activity) explaining 58% of the variance. SEM analyses showed strong significant associations between anthropometrics (body mass index, neck circumference, waist circumference) (0.45), OSA-related symptoms (snoring, witnessed apnoeas, dry mouth) (0.47) and AHI. No direct effects of OSA on comorbidities, blood pressure, dyssomnia or self-rated health were observed. CONCLUSION OSA was highly prevalent and was directly associated with anthropometrics and OSA-related symptoms (snoring, witnessed apnoeas and dry mouth in the morning). When meeting patients with hypertension, these characteristics could be used by general practitioners to identify patients who are in need of referral to a sleep clinic for OSA evaluation.