Correlation of exhaled nitric oxide levels and airway inflammation markers in stable asthmatic patients.

Monitoring of inflammation is an important factor in asthma management. The gold standard for measuring direct airway inflammation is bronchial biopsy specimens taken from proximal airways through a fiberoptic bronchoscope. As a noninvasive procedure, the use of exhaled nitric oxide (FENO) for monitoring airway inflammation has been reported in many studies. The aim of this study was to evaluate the correlation of FENO with direct measurements of airway inflammation in biopsy specimens and pulmonary function tests (PFT). Histopathologic features were observed on bronchial biopsy specimens obtained from nine stable mild-moderate asthmatics. Each subject had measurements of PFT, FENO levels, blood eosinophil count, and bronchoscopy with bronchial biopsies and bronchoalveolar lavage. Five subjects with forced expiratory volume in 1 second >80% had methacholine challenge test. None of the subjects had prior anti-inflammatory therapy for asthma. No correlation was found between PFT, blood eosinophil count, and FENO levels. There was a negative correlation between PC20 and FENO. Though there was no correlation between bronchial biopsy eosinophil, monocyte and lymphocyte counts, and FENO, we found a weak positive correlation between total inflammatory cell count in bronchial biopsies and FENO levels. A negative significant correlation was found between FENO levels and epithelial desquamation (p<0.05, r=-0.7). These results suggest that, FENO levels reflect the increased number of activated inflammatory cells in airways and the negative correlation with epithelial desquamation reflects the role of epithelium in NO syntheses. FENO should not be interpreted as a specific inflammation marker for asthma.