Objectives: Variability of clinical phenotypes in childhood obstructive sleep apnoea (OSA) has prompted research for biomarkers to identify patients at risk of developing OSA-related complications. Upper airway inflammation is documented in children with OSA. Whether it is related to end-organ morbidities and systemic inflammation is under-explored. The primary objectives of our study are 1)To evaluate inflammatory biomarkers with the use of nasal epithelial lining fluid (NELF) collected by nasal strips as a representation of upper airway inflammation in children with OSA compared to non-OSA controls; 2) To evaluate the associations between NELF biomarkers with ambulatory blood pressure (ABP) outcomes in children with OSA.

Hypothesis to be tested: Inflammatory biomarkers in NELF in children with OSA are altered when compared with non-OSA controls and correlated with ABP outcomes.

Design and subjects: A prospective case-control study. Non-obese Chinese children aged 6-11 years old with habitual snoring (≥3 nights per week) and polysomnography (PSG) confirmed OSA (OAHI of ≥1/hour) will be recruited as cases. Non-OSA children with OAHI < 1 event/h will be recruited as controls. All subjects will undergo evaluation including questionnaires, anthropometric measurements, PSG, 24-hour ABP measurement, blood and NELF sampling.

Primary outcome measure: Profile of inflammatory biomarkers in the NELF. Analysis: Correlations between NELF inflammatory biomarkers with polysomnographic and ABP measurements will be evaluated by regression analysis.

Expected results: This study will provide novel and important information regarding upper airway inflammatory biomarkers in children with OSA and their relationship with blood pressure outcomes.

Inclusion Criteria:

• Children aged 6-11 years old

Exclusion Criteria:

• Previous upper airway surgery, genetic or syndromal disease, congenital or acquired neuromuscular disease, suspected or confirmed congenital or acquired immunodeficiency, obesity (BMI z-score ≥1.645), known metabolic syndrome, craniofacial abnormalities, structural or congenital heart disease, use of medications or therapy that could affect immunity such as systemic corticosteroids, chemotherapy, radiation therapy, intravenous immunoglobulins.

Chinese children aged 6-11 years old with symptoms suggestive of obstructive sleep apnoea and healthy controls.