Overnight changes in exhaled carbon dioxide, oxygen, and nitrous oxide in obstructive sleep apnea: associations with disease severity and polysomnographic findings.

Exhaled breath analysis is a non-invasive approach for assessing physiological alterations in obstructive sleep apnea (OSA). This study evaluated overnight changes in exhaled CO₂, O₂, and N₂O concentrations and their associations with OSA severity and polysomnographic parameters.

Methods

In this prospective observational study, 62 adults undergoing diagnostic overnight polysomnography were enrolled and classified as having no OSA (n = 21), mild-to-moderate OSA (n = 21), or severe OSA (n = 20) according to the apnea-hypopnea index. Exhaled CO₂, O₂, and N₂O concentrations were measured immediately before and after overnight polysomnography under standardized conditions.

Results

Morning exhaled N₂O concentrations were significantly higher in patients with severe OSA than in the other groups (p = 0.001). Overnight changes in exhaled CO₂ (ΔCO₂), N₂O (ΔN₂O), and O₂ (ΔO₂) differed significantly according to OSA severity (all p < 0.001). Compared with the no OSA group, patients with OSA exhibited greater overnight increases in exhaled CO₂ and N₂O concentrations together with greater decreases in exhaled O₂ concentrations. Overnight ΔN₂O and ΔO₂ showed strong correlations with AHI (ρ = -0.760 and 0.912, respectively; both p < 0.001) and ODI (ρ = -0.713 and 0.913, respectively; both p < 0.001).&#xD;

Conclusion

Patients with OSA exhibited more pronounced overnight alterations in exhaled gas composition, particularly greater changes in exhaled O₂ and N₂O concentrations. These findings suggest that dynamic overnight exhaled gas changes may reflect physiological alterations associated with OSA severity and warrant further validation in larger prospective studies.&#xD.