Cystic Fibrosis (CF) Flow Rates Study

Inclusion Criteria: * CF * FEV1 ≥ 30% and \< 90% predicted Exclusion Criteria: * Be considered "terminally ill" or listed for lung transplantation * Have had a lung transplant * Have had a significant episode of haemoptysis (\>60 ml) in the three months prior to enrolment * Have had a myocardial infarction in the three months prior to enrolment * Have had a cerebral vascular accident in the three months prior to enrolment * Have had major ocular surgery in the three months prior to enrolment * Have had major abdominal, chest or brain surgery in the three months prior to enrolment * Have a known cerebral, aortic or abdominal aneurysm * Be breast feeding or pregnant * Be using beta blockers * Have unstable asthma