Increased alveolar nitric oxide concentration is related to nocturnal oxygen desaturation in obstructive sleep apnoea

•Alveolar exhaled nitric oxide (CANO) was increased in patients with OSA.•Increased CANO was correlated to apnoea–hypopnoea index and nocturnal desaturation.•CANO > 4.5 ppb could detect OSA patients with significant nocturnal desaturation.•These clinical findings link distal airway inflammation to intermittent hypoxia.

PurposeTo assess distal/alveolar inflammation in patients with suggestive symptoms of obstructive sleep apnoea (OSA) using exhaled nitric oxide (NO) measured by two-compartment model (2-CM) after correction for axial NO back-diffusion (trumpet model).MethodsNinety five patients suspected for OSA prospectively underwent pulmonary function test, overnight polysomnography (PSG), and exhaled NO measurement. Patients with apnoea–hypopnoea index (AHI) < 5/hour were included in non-OSA group. Exhaled NO was repeatedly measured after PSG in 21 OSA patients and 8 non-OSA subjects.ResultsAlveolar NO concentration (CANO) was significantly higher in OSA patients (n = 71; 4.07 ± 1.7ppb) as compared with non-OSA subjects (n = 24; 2.24 ± 1.06ppb; p < 0.0001) whilst maximal bronchial NO flux (J′awNO) and fractional exhaled NO (FENO) did not differ between the two groups. CANO was strongly associated to AHI (r = 0.701; p < 0.0001) and to recording time with SaO2 < 90% (ST-90%; r = 0.659; p < 0.0001) in OSA patients but not in non-OSA persons. The area under ROC curve for screening patients with OSA and significant nocturnal oxygen desaturation (ST-90% > 1%) was 0.865 ± 0.036 (95% IC, 0.793–0.937; p < 0.0001). CANO at 4.5 ppb could detect these patients with specificity of 94% and sensitivity of 46%. Increase of CANO measured after PSG was significantly related to oxygen desaturation index (ST-90%) in OSA patients.ConclusionsIncreased alveolar NO concentration was related to the severity of nocturnal oxygen desaturation in patients with OSA, linking the distal airway inflammation to intermittent hypoxia. (250 words)