Neurophysiology of Cough Reflex Hypersensitivity

Inclusion Criteria: Healthy volunteers inclusion: * Over 18 years * Measurable cough reflex sensitivity - required as is the primary end-point * No current or past history of chronic cough or chronic respiratory disease Chronic Cough Patients inclusion: * Over 18 years * Chronic persistent cough (\> 8 weeks) despite investigation and/or treatment trials for cough variant asthma/post-nasal drip and gastro-oesophageal reflux * Normal chest radiograph - primary respiratory cause for cough excluded * Normal lung function - primary respiratory cause for cough excluded Measurable cough reflex sensitivity - required as primary end-point Exclusion Criteria: * Recent upper respiratory tract infection (\<4 weeks) - this can lead to increased sensitivity of the cough reflex which resolves as the infection settles * Pregnancy/breast-feeding - unknown effects of oesophageal acid infusion * Current smokers or ex-smokers with \< 6 month abstinence or history \> 20 pack years - smoking can alter the sensitivity of the cough reflex * Opiate or ACE inhibitor use or centrally acting medication - can alter the cough reflex sensitivity * Symptomatic gastro-oesophageal reflux, post-nasal drip or asthma (chronic cough cohort may have been treated for these in the past but cough did not resolve) - these conditions are known to cause cough and alter cough reflex sensitivity * Significant ongoing chronic respiratory/cardiovascular/gastro-intestinal/haematological/ neurological/psychiatric illnes…