Cough Responses to Tussive Agents in Health and Disease

Inclusion Criteria: * General * Adult subjects aged 18 years and over * Meet criteria for subject groups as outlined below (1) Healthy volunteers * Non-smokers * No history of respiratory disease (2) Healthy smokers * Current smokers with smoking history of ≥10 pack years * Spirometry within normal limits i.e. FEV1\>80% predicted and FEV1/FVC ratio \>75% predicted (3) Asthma * Physician diagnosis of asthma * Airways hyperresponsiveness to methacholine; PC20\<16mg/ml (within last 2 years) * Non-smokers or ex-smoker with smoking history of ≤10 pack years (4) COPD * Physician diagnosis of COPD * Ex-smokers with smoking history of ≥20 pack years * Spirometry demonstrating airflow obstruction i.e. FEV1/FVC ratio \<70% (5) Chronic Cough * History of a dry cough for \>8 weeks * Normal CXR * Non-smokers or ex-smoker with smoking history of ≤10 pack years Exclusion Criteria: * 1\) Symptoms of upper respiratory tract infection within the last 6 weeks 2) Participation in another clinical trial of an investigational drug within the last 4 weeks 3) Use of medication likely to alter cough reflex sensitivity i.e. ACE inhibitors, codeine phosphate, morphine sulphate, 4) Patients with severe respiratory disease i.e. FEV1 \< 1 litre, 5) Significant medical co-morbidities likely to affect ability to participate in the trial or affect cough reflex sensitivity e.g. diabetes, stroke, Parkinson's disease, multiple sclerosis etc.