Exhaled nitric oxide and exhaled breath condensate pH as predictors of sputum cell counts in optimally treated asthmatic smokers

Abstract

Smoking is thought to modify the pattern of airway inflammation. Induced sputum provides useful information on cellular phenotype in inflammatory airways disorders; however, it is time-consuming and difficult to implement in everyday clinical practice. The aim of this study was to determine whether exhaled NO (FeNO) and exhaled breath condensate (EBC) pH differed in asthmatic smokers compared with asthmatic non-smokers and healthy subjects, and to evaluate the performance of FeNO and EBC pH for predicting the cellular phenotype of induced sputum. Asthmatic smokers (n = 40) and non-smoking asthmatic patients (n = 43) were recruited for the study. Healthy smoking (n = 30) or non-smoking (n = 30) subjects served as controls. FeNO and EBC pH were measured and all subjects underwent sputum induction for assessment of cell counts. EBC pH was significantly lower in asthmatic smokers compared with non-smokers (P < 0.01). FeNO levels were also significantly lower in asthmatic smokers compared with non-smokers (P < 0.001). EBC pH was inversely associated with sputum eosinophils in both asthmatic smokers and non-smokers (P < 0.001), whereas it was inversely associated with sputum neutrophils only in asthmatic smokers (P < 0.001). FeNO was positively associated with sputum eosinophils both in asthmatic smokers and non-smokers (P < 0.001) but was not associated with sputum neutrophils. In asthmatic smokers, FeNO was a better predictor of sputum eosinophilia, whereas EBC pH was a better predictor of sputum neutrophilia. A combination of FeNO ≤ 14 ppb together with EBC pH > 7.20 predicted the paucigranulocytic induced sputum phenotype. EBC pH and FeNO levels were significantly lower in asthmatic smokers compared with non-smokers. Combined specific cut-off levels for FeNO and EBC pH may predict the paucigranulocytic phenotype in asthmatic smokers.