The sensitivity of a person's cough reflex can be measured by getting them to breathe in (inhale) irritant chemicals. There are different methods by which subjects are asked to inhale these chemicals, either by taking one deep breath in, or by asking them to just continue to take a number of breaths. The purpose of this clinical research study is to see if the coughing responses are different in healthy people and people with respiratory problems that make them cough when they are given these chemicals in these two methods.

Inclusion Criteria:

• Adult subjects aged 18 and over.

Meet criteria for subject groups as outlined below:

Healthy volunteers:

• Must be non smokers.
• No history of respiratory disease.

Healthy smokers:

• Current smokers with at least 10 pack year history of smoking.
• Spirometry within normal limits i.e. FEV1 > 80% predicted and FEV1/FVC ratio of > 75% predicted.

Asthma:

• Physician diagnosis of asthma
• Stable asthma.
• Airway hyperresponsiveness to methacoline; PC20< 16mg/ml.
• Non smokers or ex-smokers with smoking history of less than 10 pack years.

COPD:

• Physician diagnosis of COPD
• Ex smokers with smoking history of at least 20 pack years
• Spirometry demonstating evidence of airflow obstruction i.e. FEV1/FVC ratio of < 70%

Chronic cough:

• History of dry cough for at least 8 weeks.
• Normal chest x ray.
• Non smokers or ex smokers of less than 10 pack years history of smoking.

Exclusion Criteria:

• Symptoms of upper respiratory tract infection within the last 4 weeks.
• Participation in another clinical trial of an investigational drug within 4 weeks.
• Use of medication likely to alter cough reflex sensitivity i.e. ACE inhibitors, codeine phosphate, morphine sulphate.
• Patients with severe respiratory disease i.e. FEV1 < 1.0 litre.
• Use of steroid tablets in previous 2 months or taken more than 3 courses of steroid tablets in the preceding 12 months in subjects with asthma or COPD.
• Change in asthma treatment in the preceding 6 weeks in asthma group
• 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.

Selected from secondary care.