Cough frequency in children with mild asthma correlates with sputum neutrophil count

Albert M Li ^1*, Tony WT Tsang ¹, Dorothy FY Chan ¹, Hugh S Lam ¹, Hung K So ¹, Rita YT Sung ¹ and Tai F Fok ¹

¹ Chinese University of Hong Kong, Hong Kong

^* To whom correspondence should be addressed. E-mail: albertmli{at}cuhk.edu.hk.

Accepted 3 April 2006

Abstract

Objectives: To (1) measure cough frequency in children with stable asthma using a validated monitoring device, and (2) assess the correlation between cough frequency with the degree and type of airway inflammation.

Methods: Thirty-six children with a median age of 11.5 years (IQR: 9-14) with stable asthma were recruited. They underwent spirometric testing, exhaled nitric oxide (eNO) measurement, sputum induction for differential cell count, and ambulatory cough monitoring for 24 hours. Coughing episodes were counted both as individual spikes and as clusters.

Results: All children had mild intermittent asthma and their median forced expiratory volume in 1 second (FEV1) and eNO were 83.3% (IQR 81.1-97.6) and 56.1 ppb (IQR 37.4-105) respectively. The median number of cough episodes per day was 25.5 (IQR 16-42.8). Sputum induction was successful in 69% of the subjects and cough frequency was found to have a significant positive correlation with sputum neutrophil count (r=0.833, p=0.0001).

Conclusions: Children with stable mild asthma have increased cough frequency that might be driven by a neutrophilic inflammatory pathway.

Keywords: asthma, children, cough, neutrophilic inflammation

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