ToAST:Investigating the Effect of Bronchial Thermoplasty on Cough in Patients With Severe Asthma

Inclusion Criteria: * Aged ≥18 * Person with an established diagnosis of severe asthma * All patients should be on British Thoracic Society (BTS) steps 4 or 5 * Patients who have had bronchial thermoplasty (BT) should be at least 2 months after their treatment * Historical evidence of one of the following: * Airway reversibility to a short acting beta-2 agonist of ≥12% * Bronchial hyper-responsiveness (PC20\<8mg/ml) * Fractional exhaled nitric oxide ≥50ppb * Peak flow variability \>8% * Raised serum (≥0.45) or sputum eosinophilia (\>3%) * Variability in spirometry over 24 months of \>20% Exclusion Criteria: * Unable to give informed consent * FEV1\<50% predicted or \< 1 litre * Known allergy or intolerance to capsaicin * Symptoms of upper respiratory tract infection in the last 1 month which have not resolved. * Lower respiratory tract infection or pneumonia in the last 6 weeks. * Current smoker or ex-smoker with ≥10 pack year smoking history, abstinence of ≤6 months * Asthma exacerbation in the previous month requiring an increase or starting of an ICS or OCS * Subject has changed asthma medication within the past 4 weeks prior to screening * A previous asthma exacerbation requiring Intensive Care Unit (ICU) admission. * Significant other pulmonary disorders as the major diagnosis, in particular: pulmonary embolism, pulmonary hypertension, interstitial lung disease, lung cancer, cystic fibrosis, emphysema or bronchiectasis. * Evidence of vocal cord dysfunction * Pregnancy or breast-feeding * Use of ACE inhibitors * Any centrally acting medication which in the view of the investigator could alter the sensitivity of the cough reflex\* * History of psychiatric illness, drug or alcohol abuse which may interfere in the participation of the trial.