- Diagnosis of asthma: This will be established symptomatically by episodic wheezing, chest tightness and/or dyspnoea and objectively confirmed by methacholine airway hyperresponsiveness or by evidence of variable airflow obstruction with an increase in FEV1 of > 12% following nebulised salbutamol (2.5mg) or diurnal peak flow variability of > 20% for 3 days in a week (with a minimum change of 60 L) during the run-in period of the study (BTS).