Exhaled nitric oxide from the central airway and alveoli in OSAHS patients: the potential correlations and clinical implications

Background The aim of the study was to evaluate exhaled nitric oxide (eNO) derived from different areas of airway in obstructive sleep apnea hypopnea syndrome (OSAHS) patients with NO exchange model and investigate the potential application and interpretation of eNO in clinical setting. Methods This study was divided into two parts. Firstly, we performed a case control study in 32 OSAHS patients and 27 non-OSAHS participants. Fractional eNO (FeNO) and eNO from the central airway (J’awNO) and from alveoli (C A NO) were compared in OSAHS and control groups. Also, correlation of eNO to severity of OSAHS was analyzed. Secondly, a prospective study was conducted in 30 severe OSAHS patients who received a short-term nasal continuous positive airway pressure (nCPAP) treatment. We evaluated eNO, plasma ET-1 concentration, and echocardiography during the treatment process and explored the potential relationship among them. Results FeNO and J’awNO were higher in OSAHS and associated with disease severity, while C A NO was relatively lower. After nCPAP treatment in severe OSAHS patients, FeNO and J’awNO decreased and C A NO increased significantly. Substantial agreement was shown between the elevation of C A NO and the decrease of plasma ET-1 concentration after nCPAP by Kappa analysis for consistency. Tei index, which is considered indicative of global right ventricular function, might be predicted by plasma ET-1 levels in severe OSAHS patients. Conclusions NO exchange model provides us with more information of eNO derived from different areas. eNO is not only confirmed to be an effective method for airway inflammation evaluation in the follow-up of OSAHS, C A NO may also serve as a useful marker in monitoring endothelial function, resistance of pulmonary circulation, and right ventricular function for clinical implication.