Association between peripheral airway function and neutrophilic inflammation in asthma

• Published in: Respirology (Carlton, Vic.) Vol. 20; no. 6; pp. 975 - 981
• Main Authors: Farah, Claude S., Keulers, Laurien A.B., Hardaker, Kate M., Peters, Matthew J., Berend, Norbert, Postma, Dirkje S., Salome, Cheryl M., King, Gregory G.
• Format: Journal Article
• Language: English
• Published: Australia Blackwell Publishing Ltd 01.08.2015
• Subjects: Adult; asthma; Asthma - pathology; Asthma - physiopathology; Breath Tests; Bronchi - physiopathology; Cross-Sectional Studies; Female; Humans; Inflammation - physiopathology; Male; Middle Aged; multiple breath washout; neutrophil; Neutrophils - pathology; Neutrophils - physiology; small airway; Spirometry; Sputum - cytology; ventilation heterogeneity; Young Adult; ventilation heterogeneity; asthma; multiple breath washout; neutrophil; small airway
• ISSN: 1323-7799; 1440-1843; 1440-1843
• DOI: 10.1111/resp.12550

Background and objective Small airway dysfunction is associated with asthma severity and control, but its association with airway inflammation is unknown. The aim was to determine the association between sputum inflammatory cells and the site of small airway dysfunction, measured by multiple breath nitrogen washout in convection‐dependent (Scond) and more peripheral diffusion‐dependent (Sacin) airways. Methods Fifty‐three (20–67 years) subjects with asthma on inhaled corticosteroid (ICS) treatment were characterized by spirometry, Scond, Sacin and induced sputum differential counts. %Predicted values for Scond and Sacin were calculated from published reference equations to adjust for the effects of age. Univariate correlations were assessed using the Spearman test. Multivariate linear regressions were performed to account for potential confounders, including age, gender, disease duration, body mass index and ICS dose. Results Sacin (%predicted) correlated significantly with neutrophil% (rs = 0.33, P = 0.02), ICS dose (rs = −0.28, P = 0.04) and age (rs = 0.27, P = 0.05). In multivariate analysis, Sacin related only to neutrophil% (adjusted R2 = 0.18, P = 0.001). Scond (%predicted) correlated significantly only with eosinophil% (rs = 0.39, P = 0.004). There was a trend for a negative relationship with ICS dose (rs = −0.26, P = 0.06). In multivariate analysis, Scond related to eosinophil% and ICS dose independently (adjusted R2 = 0.12, P = 0.02). Conclusions Acinar and conductive airway dysfunction is associated with different inflammatory profiles in asthmatic airways, independently of the effects of age and disease duration. The association between acinar airway dysfunction and neutrophilic airway inflammation may have implications for asthma treatment. The aim of this cross‐sectional study was to determine the association between sputum inflammatory cells and small airway dysfunction in asthma. This is the first report of an association between small airway dysfunction and neutrophilic airway inflammation. The results may have implications for asthma treatment.