Exhaled nitric oxide concentrations (FENO), expressed as ppm, in 3 groups: COPD (36), COPD+PAH (12), and healthy subjects (HS) (15). Significance was established at a p value < 0.05. The horizontal lines represent median value. FENO levels were significantly higher in COPD only, compared to both the COPD with PAH (p = 0.03), and the controls (p = 0.003). There was no significant relationship between FENO levels in COPD+PAH compared to the control group levels (p = 0.45).