The study will have a maximum of 4 visits separated by at least 24 hours. The first 2 visits will determine eligibility. All eligible subjects will be invited back for a third and a fourth visit.~Screening Period (Visits 1 and 2) - For All Subjects Eligible subjects will be identified during the initial screening procedures with measures of spirometry, hyperresponsiveness to methacholine, complete history, physical examination, allergen skin test, and mannitol cough challenge. The screening procedures will be conducted over 2 separate visits.~Effects of Salbutamol (Visit 3 and 4) - For Healthy Control Subjects, Twenty subjects with no evidence of asthma will return for visit 3 and 4. These visits must be at least 24h apart and no longer than 7 days. Health controls will first receive salbutamol 2.5mg or saline placebo via a nebuliser and 15 mins later the forced expiratory volume at one second (FEV1) measured. Subjects will then undergo a mannitol cough challenge exactly like the previous mannitol cough challenges. These data will be used for determining the effects of salbutamol on mannitol-induced cough.~Visit Windows Each visit must be separated by a minimum of 24 hours, and a maximum of 7 days. Study visits can be performed in the morning or afternoon, however for each subject the timing should be consistent with Visits 2 at the same time of day ± 2 hours
The study aim is to investigate if changes in osmolarity using mannitol challenge can evoke coughing healthy controls with no evidence of bronchoconstriction (PC20>16mg/ml or mannitol PD15 > 635 mg, or < 10% incremental fall in FEV1 between consecutive mannitol doses) and if salbutamol can affect this. This is a double-blind, placebo-controlled analysis in healthy controls assessing the effects of salbutamol on mannitol induced cough.