Exhaled nitric oxide in specific challenge tests to assess occupational asthma

Abstract

Exhaled nitric oxide (NO) is a marker of eosinophilic inflammation of the airway mucosa accompanying changes in the clinical condition of asthma. Allergen exposure has been associated with delayed elevation of exhaled NO. The aim of this study was to assess the asthmatic airway inflammation with exhaled NO measurements during specific bronchial challenge tests with occupational agents. Forty patients with suspected occupational asthma were investigated. Specific bronchial challenge tests were performed with forced expiratory volume in one second or peak expiratory flow follow-up, supplemented by exhaled NO measurements before and 24 h after challenge tests. In active challenges, which induced bronchoconstriction, a significant mean increase of exhaled NO concentration was noted. In patients with a normal or slightly increased (<14.5 parts per billion (ppb)) basal NO level and a late bronchoconstriction, a significant increase in exhaled NO was seen. Patients with a high basal NO level (>14.5 ppb) and a significant bronchoconstriction did not show a significant NO elevation. Challenge tests without bronchoconstriction were not associated with a significant elevation of exhaled NO. Exhaled nitric oxide measurements can be used to indicate the development of airway inflammation accompanying late asthmatic reaction after bronchial challenge tests in patients with a normal or slightly increased basal nitric oxide concentration.