Temporal Dynamics of Fractional Exhaled Nitric Oxide (FeNO) During CPAP Therapy in Obstructive Sleep Apnea: A...

This study aimed to assess: (i) whether long-term continuous positive airway pressure (CPAP) reduces fractional exhaled nitric oxide (FeNO) in obstructive sleep apnea (OSA), and (ii) how FeNO change relates to baseline OSA severity. Unlike prior cross-sectional work, we performed a prospective longitudinal follow-up with FeNO at baseline, after short-term titration, and at three months. Primary and secondary endpoints were prespecified.

We enrolled 62 patients with moderate-to-severe OSA; 43 completed CPAP titration and three-month follow-up. FeNO was measured preCPAP, after two nights (postCPAP1), and at three months (postCPAP2). Secondary analyses examined correlations between FeNO change and baseline indices-apnea-hypopnea index (AHI), oxygen desaturation index (ODI), percent sleep time with SpO₂ < 90% (TS90%), and Epworth Sleepiness Scale (ESS)-and the effect of CPAP adherence. Statistics: normality (Shapiro-Wilk); t-test or Mann-Whitney U; χ²/Fisher's exact for categorical data; repeated-measures ANOVA with Huynh-Feldt for longitudinal change; Spearman correlations. Missing data were handled by complete-case analysis with multiple imputation (m = 5) as sensitivity.

At baseline, FeNO was higher in OSA than in AHI < 15 reference subjects from our earlier cohort (21.49 ± 5.56 vs 13.28 ± 3.70 ppb, P < 0.001). Within the OSA cohort, FeNO rose slightly after titration (22.84 ± 4.58 ppb, P > 0.05) but decreased significantly after 3 months of treatment (17.95 ± 3.27 ppb, P < 0.001 vs baseline).FeNO reduction correlated with AHI (r = 0.674), ODI (r = 0.617), TS90% (r = 0.461), and ESS (r = 0.552; all P < 0.001). Greater reductions occurred with adherence ≥ 6 h/night.

Sustained CPAP significantly lowers FeNO, reflecting reduced airway inflammation in OSA. FeNO may serve as a promising non-invasive candidate biomarker for monitoring CPAP response, but larger multicenter studies are needed.