The present study has the following objectives:~to evaluate the relationship between BHR and mid-expiratory flow, to assess the diagnostic accuracy of fractional exhaled nitric oxide，impulse oscillometry and mid-expiratory flow in CVA with special regard to its discriminating value between CVA and other causes of a chronic cough, to estimate prognostic value of BHR and fractional exhaled nitric oxide (FeNO) count in predicting response to asthma treatment.
The aim of the research is to evaluate the clinical value of fractional exhaled nitric oxide(FeNO) ,impulse oscillometry(IOS) and mid-expiratory flow (MEF) in patients with cough variant asthma.