Exhaled carbon monoxide levels in obstructive sleep apnoea

摘要

Background: Obstructive sleep apnoea (OSA) is characterised by chronic intermittent hypoxia, which enhances airway inflammation and oxidative stress. Exhaled carbon monoxide (eCO), a marker for oxidative stress, has been investigated in OSA. However, previous studies could be biased as they did not differentiate patients with OSA based on smoking history, a known factor influencing eCO levels. The aim of this study to investigate eCO levels in patients with OSA and non-OSA controls and compare evening to morning results. Methods: Exhaled carbon monoxide concentration was measured in the evening and in the morning following an in-hospital cardiorespiratory polygraphy in 60 never-smoker OSA patients, 14 ex-smoker OSA patients, 39 current-smoker OSA patients, 10 never-smoker asthmatic patients with OSA, 16COPDpatients with OSA and 20 never-smoker non- OSA controls. OSA was diagnosed based on the apnoea-hypopnoea index (AHI > 5/h). Results: There was no difference between the never-smoker controls and never-smoker patients with OSA either in the evening (1.98 ± 1.00 ppm versus 1.95 ± 1.28 ppm, p = 0.57, OSA versus controls, respectively) or morning (1.95 ± 0.96 ppm versus 1.80 ± 0.95 ppm, p = 0.42), however there was a weak correlation between eCO and AHI in the evening (r = 0.31, p = 0.01). Accordingly, patients with severe OSA had higher eCO levels in the evening (2.43 ± 1.12 ppm) compared to mild OSA patients (1.57 ± 0.87 ppm, p < 0.01). Ex-smoker (3.07 ± 2.23 ppm), current-smoker (13.13 ± 11.35 ppm), asthmatic (2.70 ± 1.16 ppm) and COPD(18.25 ± 18.60 ppm) patients with OSA had higher levels of eCO compared to the non-smoker OSA group. Conclusion: Exhaled carbon monoxide is elevated only in severe never-smoker OSA suggesting accelerated oxidative stress. Previous smoking history is a major influencing factor which may explain differences between our findings and those of previous studies. Although our results show some impact of OSA on eCO measurements, the