Exhaled Nitric Oxide as a Potential Biomarker of Continuous Positive Airway Pressure Therapy for Severe Obstructive Sleep Apnea Patients

Objective: The aim of the present study was to measure the correlation between the level of exhaled Nitric Oxide (NO) and Obstructive Sleep Apnea (OSA) severity and to evaluate its modification after Continuous Positive Airway Pressure (CPAP) treatment in severe OSA patients. Methods: It was a descriptive and cross-sectional study. Subjects were classified by mild-moderate or severe OSA. CPAP was used for severe OSA patients and followed up for 3 months. Exhaled NO was measured in the morning after the previous night of Respiratory Polygraphy (RPG) recording. Results: This study recruited 123 subjects, including 40 mild-moderate and 83 severe OSA patients. The level of maximum bronchial NO production (J’awNO) in patients with severe OSA was significantly higher than mild-moderate OSA [36.2 (6.1–92.2) vs. 19.6 (1.6-73.0) ppb; p=0.001)]. The level of concentration of NO in the gas phase of the alveolar (CANO) in patients with severe OSA was lower than mild-moderate OSA [5.2 (1.2-12.7) vs. 6.9 (0.8-14.0) ppb; p=0.002). The total flux of NO in the conducting airway compartment (J’awNO) and CANO were correlated with an apnea-hypopnea index (AHI) (rho=0.25 and p=0.02; rho= 0.18 and p=0.04, respectively). There was a weak significant correlation between J’awNO and nadir SpO2 in patients with OSA (rho = -0.22 and p= 0.023). After 3-month treatment with CPAP, the level of J’awNO was significantly reduced in patients with severe OSA [23.4 (12.9-44.5) vs. 33.1 (21.2-55.0); p<0.001. Conclusion: J’awNO is proportionally increased in patients with severe OSA and reduced after treatment with CPAP. Thus, J’awNO may be used as a relevant and surrogate biomarker of severe OSA.