Exhaled Nitric Oxide in Patients with Obstructive Sleep Apnea Syndrome

Exhaled nitric oxide has been extensively investigated as a non-invasive marker of airway inflammation. Some authors have suggested that morning FE_NO in obstructive sleep apnea syndrome (OSAS) patients is elevated due to inflammation of upper airways, while others have not found any differences between patients and healthy subjects. The purpose of this study was to analyze concentration of exhaled nitric oxide (FE_NO) in OSAS patients. Methods: 119 (99 M, 20 F) consecutive patients of sleep laboratory participated in this study. Standard overnight sleep studies with polysomnography or portable screening device were carried out in the whole group: OSAS was diagnosed in 66 patients and 53 no-OSAS served as controls. FE_NO was measured on-line with a flow rate kept at 0.045–0.055 l/s, according to the recommendations of ATS using a chemiluminescence analyzer twice: before the sleep study (8–10 p.m.) and after termination of data collection (6–8 a.m.). There were no differences in age between patients and controls. Respiratory disturbance index (RDI) was 40.3 ± 24.9 in patients and 3.7 ± 2.8 in con-trols (p < 0.001). In OSAS patients both evening and morning FENO was significantly higher compared to controls(23.1 ± 14.8 ppb vs. 16.8 ± 9.8 ppb and 22.4 ± 13.2 ppb vs. 15.3 ± 8.1 ppb respectively, p < 0.05). Weak but statistically significant correlations for the whole group between morning FE_NO and mean and minimum arterial oxygen saturation (SaO₂) during sleep and number of study minutes with SaO₂ < 90% were observed. Lower evening FE_NO in OSAS patients with coexisting arterial hypertension when compared to normotensive OSAS patients was also noticed (19.1 ± 10.8 ppb vs. 27.1 ± 19.1 ppb; p < 0.05). Conclusions: The increase in FE_NO in OSAS patents may be caused by repetitive apneas and hypoxemia during sleep.