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The sensitivity of a persons cough reflex can be measured by getting them to breath in (inhale) irritant chemicals. The purpose of this clinical research study is to test the sensitivity of the cough reflex to a variety of chemicals that can be inhaled to see if coughing responses are different between healthy people and people with respiratory problems that make them cough.
Full description
Coughing is a distressing symptom which has a major impact on quality of life. It has been estimated that cough costs the UK economy £1 billion each year. Currently there are no effective anti-tussive agents to treat subjects with cough. Although drugs such as morphine may have some anti-tussive effect, side effects unacceptable.
Currently our understanding of the mechanisms which lead to coughing in different diseases is poor. Many mechanistic studies rely on testing the sensitivity of the cough reflex by inhalation of capsaicin (chilli-pepper extract) or citric acid. These challenges do not differentiate well between health and disease or between different disease states. Other agents such as prostaglandins and bradykinin are known to stimulate a coughing but responses to these agents have rarely been used as a measure of cough reflex sensitivity and not been compared to standard challenges.
It is clear that patients with common airway diseases such as COPD and asthma cough significantly more than healthy subjects. Moreover subjects presenting with chronic cough have cough rates an order of magnitude higher than most patients with airway disease. These differences are poorly represented by the differences in current cough challenge tests.
The investigators hypothesize that patterns of cough responses to different tussive agent may better differentiate between health and different disease states. These patterns may also suggest the different mechanisms leading to cough in different diseases.
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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
102 participants in 5 patient groups
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Data sourced from clinicaltrials.gov
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