A Study to Determine the Variability of a 6-Minute Walk Test in Cystic Fibrosis Subjects With Advanced Lung Disease

This is an observational study to be conducted at approximately 25 sites in the United States. Approximately 25 subjects with severe obstructive CF lung disease (FVC <40% predicted) will be enrolled.

Inclusion Criteria:

• Able to provide written informed consent
• Males or females who will be >=14 years old at Visit 3
• A proven diagnosis of CF as evidenced by a positive sweat test (sweat sodium or chloride >60 mEq/L by quantitative pilocarpine iontophoresis), or genotype and clinical symptoms consistent with the diagnosis of CF
• Able to perform reproducible spirometry maneuvers at Visit 1 in accordance with the American Thoracic Society (coefficient of variation for three FEV1 maneuvers <=0.2)
• FVC <40% predicted for height, age and sex at Visit 1
• On a stable regimen of chest physiotherapy (CPT) begun at least 7 days prior to Visit 1
• Able to complete the 6-minute walk test at Visit 1

Exclusion Criteria:

• Use of an investigational drug or device within 28 days prior to Visit 1
• Experiencing an episode of severe acute respiratory failure, as determined by the investigator