Correlation of Exhaled Nitric Oxide Levels and Airway Inflammation Markers in Stable Asthmatic Patients

Abstract

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 (Fe_NO) for monitoring airway inflammation has been reported in many studies. The aim of this study was to evaluate the correlation of Fe_NO 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, Fe_NO 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 Fe_NO levels. There was a negative correlation between PC20 and Fe_NO. Though there was no correlation between bronchial biopsy eosinophil, monocyte and lymphocyte counts, and Fe_NO, we found a weak positive correlation between total inflammatory cell count in bronchial biopsies and Fe_NO levels. A negative significant correlation was found between Fe_NO levels and epithelial desquamation (p<0.05, r = −0.7). These results suggest that, Fe_NO 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. Fe_NO should not be interpreted as a specific inflammation marker for asthma.

• Asthma
• Bronchial biopsy
• Nitric oxide