RecruitingDiagnostic testDetection of Unsuspected Small Airways Obstruction in Cystic FibrosisGoal is to physiologically detect unsuspected small airways obstruction in children and adults with treated heterozygous and homozygous cystic fibrosis. Unsuspected refers to normal routine pre bronchodilator spirometry including normal FEV1(L), FVC (L). and FEV1/FVC%. This is a retrospective study.