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Association Between Neutrophilic Airway Inflammation and Airflow Limitation in Adults With Asthma^*

^* From the Institute for Lung Health, Department of Respiratory Medicine and Thoracic Surgery, Glenfield Hospital, Leicester, UK.

Correspondence to: Dominick E. Shaw, MRCP, Institute for Lung Health, Department of Respiratory Medicine and Thoracic Surgery, Glenfield Hospital, Leicester LE3 9QP, UK; e-mail: dominickshaw{at}doctors.org.uk

Abstract

Background: There is debate about the mechanisms of persistent airflow limitation in patients with asthma. Chronic inflammation is assumed to be important, although there is limited and contradictory information about the relationship between airway inflammation and postbronchodilator FEV₁.

Methods: We have assessed the cross-sectional relationship between prebronchodilator and postbronchodilator FEV₁ and measures of airway inflammation after allowing for the effects of potential confounding factors. Multivariate analysis was performed on data collected from 1,197 consecutive patients with asthma seen at the respiratory outpatient clinic at Glenfield Hospital between 1997 and 2004. Relationships between induced sputum total neutrophil and differential eosinophil cell counts, and prebronchodilator and postbronchodilator lung function were examined.

Results: Sputum total neutrophil but not differential eosinophil count was associated with lower postbronchodilator FEV₁. Both differential eosinophil and total neutrophil count were associated with lower prebronchodilator FEV₁. These effects were independent after adjustment for age, smoking, ethnicity, asthma duration, and inhaled corticosteroid use. A 10-fold increase in neutrophil count was associated with a 92 mL reduction (95% confidence interval, 29 to 158; p = 0.007) in postbronchodilator FEV₁.

Conclusions: In this large heterogeneous population of adults with asthma, we have shown that prebronchodilator FEV₁ is associated with neutrophilic and eosinophilic airway inflammation, whereas sputum total neutrophil counts alone are associated with postbronchodilator FEV₁. This supports the hypothesis that neutrophilic airway inflammation has a role in the progression of persistent airflow limitation in asthma and raises the possibility that this progression and the development of COPD share a common mechanism.

Key Words: asthma • eosinophil • induced sputum • lung function • neutrophil