Measurement of exhaled nitric oxide concentration in patients with obstructive sleep apnea: A meta-analysis

BACKGROUND: Exhaled nitric oxide (eNO) has been proposed as a noninvasive measure of airway inflammation. However, its value in patients with obstructive sleep apnea (OSA) is still controversial. The authors aim to assess the difference in eNO levels between patients with OSA and controls by a meta-analysis. METHODS: A systematic search was performed in the PubMed, EMBASE, the Cochrane Library, and MEDLINE databases to collect relevant studies published from 1996 to 2016. Eligible studies that reported eNO levels in patients with OSA were included. STATA (version 12.0) was used for data analysis. RESULTS: Two hundred eighty-four studies were reviewed for inclusion, with 16 studies pooled for analysis (16 studies for fractional exhaled nitric oxide [FENO], 5 for alveolar nitric oxide [CANO], and 4 for the maximum airway wall flux of nitric oxide [J′awNO]). The FENO levels were significantly higher in patients with OSA compared with that in the control groups (6.32 ppb, 95% confidence interval [CI] 4.46–8.33, P < 0.001). Furthermore, FENO was significantly increased (4.00 ppb, 95% CI 1.74–6.27, P = 0.001) after overnight sleep in patients with OSA, but not in healthy controls. Additionally, long-term continuous positive airway pressure (CPAP) therapy reduced FENO levels (−5.82 ppb, 95% CI −9.6 to −2.01, P < 0.001). However, the CANO (−0.01 ppb, 95% CI −1.66 to 1.64, P = 0.989) and J’awNO levels (220.32 pl/s, 95% CI −49.31 to 489.94, P = 0.109) were not significantly different between the OSA groups and non-OSA groups. CONCLUSION: The results of the meta-analysis suggest that OSA is significantly associated with airway inflammation and elevated FENO levels can be modified by long-term CPAP therapy. J’awNO and CANO levels were not significantly different between the OSA groups and control groups.