Assessment of Airway Inflammation using Exhaled Nitric Oxide and Induced Sputum During Specific Inhalation Challenges

Rationale 

Examination of sputum eosinophils and measurement of exhaled nitric oxide have been proposed as non-invasive methods of assessing airway inflammation in asthma.

Methods 

We investigated the changes in sputum eosinophils and fraction of exhaled nitric oxide (FENO) before and 24 hours after specific inhalation challenges (SICs) with occupational agents. Sputum samples were analysed using FC scan cytometry.

Twenty-eight patients with suspected occupational asthma were investigated. SIC was performed with high molecular weight agents (16 patients) or low molecular weight agents (12 patients). A positive asthmatic (bronchoconstrictive) reaction was observed in 21 patients (75%).

Results 

A significant increase in sputum eosinophils was noted between baseline conditions (2.75% ± 3.02) and 24 hours after positive SIC (5.92% ± 5.26) (p < 0.05).

Levels of FENO increased at 24 hours after positive SIC in 3 out of 21 patients (14%).

Challenge tests without bronchoconstriction were not associated with a significant elevation of FENO.

Conclusions 

In this study, no correlation was found between the increase in FENO levels and a positive SIC. More studies are needed to assess the usefulness of FENO as a marker of airway inflammation induced by specific bronchial challenge tests.