Article in Press
Imran Satia, M.D.
,
,
Kimberley Holt, MPhil
,
Huda Badri, M.D
,
Mark Woodhead, M.D
,
Kayode Ogungbenro, PhD
,
Timothy W. Felton, PhD
,
Paul M. O’Byrne, M.D
,
Stephen J. Fowler, M.D
,
Open Access
Article Info
Abstract
Background
Cough in asthma is a common and troublesome symptom. It is generally assumed coughing occurs as a consequence of bronchial hyper-responsiveness and inflammation, but the possibility that airway nerves are dysfunctional has not been fully explored.
Objectives
To investigate capsaicin evoked cough responses in a group of well-characterised mild to moderate asthma patients compared with healthy volunteers, and assess the influences of gender, atopy, lung physiology, inflammation and asthma control on these responses.
Methods
Capsaicin inhalational challenge was performed and cough responses analysed using non-linear mixed effects modelling to estimate maximal cough responses (Emax) and the dose evoking half this response (ED50).
Results
Ninety-seven stable asthmatics (median age 23yrs (IQR 21-27), 60% female) and 47 healthy volunteers (38yrs (29-47), 64% female) were recruited. Asthmatics had a higher Emax and lower ED50 than healthy volunteers. Emax was 27% higher in females (p=0.006), 46% higher in non-atopic asthma (p=0.003) compared with healthy volunteers. Also, atopic asthmatics had a 21% lower Emax than non-atopic asthmatics (p=0.04). ED50 was 65% lower in females (p=0.0001) and 71% lower in all asthmatics (p=0.0008). ED50 was also influenced by asthma control and serum IgE, whilst Emax was related to 24hr cough frequency. Age, BMI, FEV1, PC20, FeNO, blood eosinophils and inhaled steroid treatment did not influence cough parameters.
Conclusion
Stable asthmatics exhibited exaggerated capsaicin cough responses consistent with neuronal dysfunction. Non-atopic asthmatics had the highest cough responses, suggesting this mechanism may be most important in type 2-low asthma phenotypes.
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