<qa>  What is the Lung Clearance Index measured by multiple breath washout?The Lung Clearance Index, measured by multiple breath washout, is a measure of lung function that is considered a research tool in Canada as the device used to measure it is not approved by Health Canada. The study will assess lung function in patients undergoing routine lung function testing for clinical indications Cystic Fibrosis and Other Respiratory Diseases. In addition, healthy controls of different ages will be asked to perform this lung function test to gain reference data that can be used to interpret LCI in patients with lung disease. 