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

PURPOSE

To 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).

METHODS

Ninety 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.

RESULTS

Alveolar NO concentration (C(ANO)) was significantly higher in OSA patients (n = 71; 4.07 ± 1.7 ppb) as compared with non-OSA subjects (n = 24; 2.24 ± 1.06 ppb; p < 0.0001) whilst maximal bronchial NO flux (J'awNO) and fractional exhaled NO (F(ENO)) did not differ between the two groups. C(ANO) 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). C(ANO) at 4.5 ppb could detect these patients with specificity of 94% and sensitivity of 46%. Increase of C(ANO) measured after PSG was significantly related to oxygen desaturation index (ST-90%) in OSA patients.

CONCLUSIONS

Increased 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).